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Sample records for atomic hydrogen adsorbate

  1. Revisiting the inelastic electron tunneling spectroscopy of single hydrogen atom adsorbed on the Cu(100) surface.

    Science.gov (United States)

    Jiang, Zhuoling; Wang, Hao; Sanvito, Stefano; Hou, Shimin

    2015-12-21

    Inelastic electron tunneling spectroscopy (IETS) of a single hydrogen atom on the Cu(100) surface in a scanning tunneling microscopy (STM) configuration has been investigated by employing the non-equilibrium Green's function formalism combined with density functional theory. The electron-vibration interaction is treated at the level of lowest order expansion. Our calculations show that the single peak observed in the previous STM-IETS experiments is dominated by the perpendicular mode of the adsorbed H atom, while the parallel one only makes a negligible contribution even when the STM tip is laterally displaced from the top position of the H atom. This propensity of the IETS is deeply rooted in the symmetry of the vibrational modes and the characteristics of the conduction channel of the Cu-H-Cu tunneling junction, which is mainly composed of the 4s and 4pz atomic orbitals of the Cu apex atom and the 1s orbital of the adsorbed H atom. These findings are helpful for deepening our understanding of the propensity rules for IETS and promoting IETS as a more popular spectroscopic tool for molecular devices.

  2. Revisiting the inelastic electron tunneling spectroscopy of single hydrogen atom adsorbed on the Cu(100) surface

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Zhuoling; Wang, Hao [Centre for Nanoscale Science and Technology, Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871 (China); Sanvito, Stefano [School of Physics, AMBER and CRANN Institute, Trinity College, Dublin 2 (Ireland); Hou, Shimin, E-mail: smhou@pku.edu.cn [Centre for Nanoscale Science and Technology, Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871 (China); Beida Information Research (BIR), Tianjin 300457 (China)

    2015-12-21

    Inelastic electron tunneling spectroscopy (IETS) of a single hydrogen atom on the Cu(100) surface in a scanning tunneling microscopy (STM) configuration has been investigated by employing the non-equilibrium Green’s function formalism combined with density functional theory. The electron-vibration interaction is treated at the level of lowest order expansion. Our calculations show that the single peak observed in the previous STM-IETS experiments is dominated by the perpendicular mode of the adsorbed H atom, while the parallel one only makes a negligible contribution even when the STM tip is laterally displaced from the top position of the H atom. This propensity of the IETS is deeply rooted in the symmetry of the vibrational modes and the characteristics of the conduction channel of the Cu-H-Cu tunneling junction, which is mainly composed of the 4s and 4p{sub z} atomic orbitals of the Cu apex atom and the 1s orbital of the adsorbed H atom. These findings are helpful for deepening our understanding of the propensity rules for IETS and promoting IETS as a more popular spectroscopic tool for molecular devices.

  3. Theoretical study of the dynamics of atomic hydrogen adsorbed on graphene multilayers

    Science.gov (United States)

    Moaied, Mohammed; Moreno, J. A.; Caturla, M. J.; Ynduráin, Félix; Palacios, J. J.

    2015-04-01

    We present a theoretical study of the dynamics of H atoms adsorbed on graphene bilayers with Bernal stacking. First, through extensive density functional theory calculations, including van der Waals interactions, we obtain the activation barriers involved in the desorption and migration processes of a single H atom. These barriers, along with attempt rates and the energetics of H pairs, are used as input parameters in kinetic Monte Carlo simulations to study the time evolution of an initial random distribution of adsorbed H atoms. The simulations reveal that, at room temperature, H atoms occupy only one sublattice before they completely desorb or form clusters. This sublattice selectivity in the distribution of H atoms may last for sufficiently long periods of time upon lowering the temperature down to 0 ∘C . The final fate of the H atoms, namely, desorption or cluster formation, depends on the actual relative values of the activation barriers which can be tuned by doping. In some cases, a sublattice selectivity can be obtained for periods of time experimentally relevant even at room temperature. This result shows the possibility for observation and applications of the ferromagnetic state associated with such distribution.

  4. Inside the Hydrogen Atom

    CERN Document Server

    Nowakowski, M; Fierro, D Bedoya; Manjarres, A D Bermudez

    2016-01-01

    We apply the non-linear Euler-Heisenberg theory to calculate the electric field inside the hydrogen atom. We will demonstrate that the electric field calculated in the Euler-Heisenberg theory can be much smaller than the corresponding field emerging from the Maxwellian theory. In the hydrogen atom this happens only at very small distances. This effect reduces the large electric field inside the hydrogen atom calculated from the electromagnetic form-factors via the Maxwell equations. The energy content of the field is below the pair production threshold.

  5. Antiprotonic-hydrogen atoms

    International Nuclear Information System (INIS)

    Experimental studies of antiprotonic-hydrogen atoms have recently made great progress following the commissioning of the low energy antiproton facility (LEAR) at CERN in 1983. At the same time our understanding of the atomic cascade has increased considerably through measurements of the X-ray spectra. The life history of the p-bar-p atom is considered in some detail, from the initial capture of the antiproton when stopping in hydrogen, through the atomic cascade with the emission of X-rays, to the final antiproton annihilation and production of mesons. The experiments carried out at LEAR are described and the results compared with atomic cascade calculations and predictions of strong interaction effects. (author)

  6. A DFT study of halogen atoms adsorbed on graphene layers

    Energy Technology Data Exchange (ETDEWEB)

    Medeiros, Paulo V C; De Brito Mota, F; De Castilho, Caio M C [Grupo de Fisica de Superfcies e Materiais, Instituto de Fisica, Universidade Federal da Bahia, Campus Universitario da Federacao/Ondina, 40170-115 Salvador, Bahia (Brazil); Mascarenhas, Artur J S, E-mail: caio@ufba.br [Instituto Nacional de Ciencia e Tecnologia em Energia e Ambiente-INCT-E and A, Universidade Federal da Bahia, 40170-280 Salvador, Bahia (Brazil)

    2010-12-03

    In this work, ab initio density functional theory calculations were performed in order to study the structural and electronic properties of halogens (X = fluorine, chlorine, bromine or iodine) that were deposited on both sides of graphene single layers (X-graphene). The adsorption of these atoms on only one side of the layer with hydrogen atoms adsorbed on the other was also considered (H,X-graphene). The results indicate that the F-C bond in the F-graphene system causes an sp{sup 2} to sp{sup 3} transition of the carbon orbitals, and similar effects seem to occur in the H,X-graphene systems. For the other cases, two configurations are found: bonded (B) and non-bonded (NB). For the B configuration, the structural arrangement of the atoms was similar to F-graphene and H-graphene (graphane), although the electronic structures present some differences. In the NB configuration, the interaction between the adsorbed atoms and the graphene layer seems to be essentially of the van der Waals type. In these cases, the original shape of the graphene layer presents only small deviations from the pristine form and the adsorbed atoms reach equilibrium far from the sheet. The F-graphene structure has a direct bandgap of approximately 3.16 eV at the {Gamma} point, which is a value that is close to the value of 3.50 eV that was found for graphane. The Cl-graphene (B configuration), H,F-graphene and H,Cl-graphene systems have smaller bandgap values. All of the other systems present metallic behaviours. Energy calculations indicate the possible stability of these X-graphene layers, although some considerations about the possibility of spontaneous formation have to be taken into account.

  7. Polarized atomic hydrogen beam

    Energy Technology Data Exchange (ETDEWEB)

    Chan, N.; Crowe, D.M.; Lubell, M.S.; Tang, F.C.; Vasilakis, A.; Mulligan, F.J.; Slevin, J.

    1988-12-01

    We describe the design and operating characteristics of a simple polarized atomic hydrogen beam particularly suitable for applications to crossed beams experiments. In addition to experimental measurements, we present the results of detailed computer models, using Monte-Carlo ray tracing techniques, optical analogs, and phase-space methods, that not only provide us with a confirmation of our measurement, but also allow us to characterize the density, polarization, and atomic fraction of the beam at all points along its path. As a subsidiary result, we also present measurements of the relative and absolute efficiencies of the V/G Supavac mass analyzer for masses 1 and 2.

  8. Stable atomic hydrogen: Polarized atomic beam source

    International Nuclear Information System (INIS)

    We have carried out experiments with stable atomic hydrogen with a view to possible applications in polarized targets or polarized atomic beam sources. Recent results from the stabilization apparatus are described. The first stable atomic hydrogen beam source based on the microwave extraction method (which is being tested ) is presented. The effect of the stabilized hydrogen gas density on the properties of the source is discussed. (orig.)

  9. Linear hydrogen adsorbate structures on graphite induced by self-assembled molecular monolayers

    DEFF Research Database (Denmark)

    Nilsson, Louis; Sljivancanin, Zeljko; Balog, Richard;

    2012-01-01

    Combined scanning tunnelling microscopy measurements and density functional theory calculations reveal a method to induce linear structures of hydrogen adsorbates on graphite by covering the surface with a self-assembled molecular monolayer of cyanuric acid and exposing it to atomic hydrogen...

  10. Sampling the Hydrogen Atom

    Directory of Open Access Journals (Sweden)

    Graves N.

    2013-01-01

    Full Text Available A model is proposed for the hydrogen atom in which the electron is an objectively real particle orbiting at very near to light speed. The model is based on the postulate that certain velocity terms associated with orbiting bodies can be considered as being af- fected by relativity. This leads to a model for the atom in which the stable electron orbits are associated with orbital velocities where Gamma is n /α , leading to the idea that it is Gamma that is quantized and not angular momentum as in the Bohr and other models. The model provides a mechanism which leads to quantization of energy levels within the atom and also provides a simple mechanical explanation for the Fine Struc- ture Constant. The mechanism is closely associated with the Sampling theorem and the related phenomenon of aliasing developed in the mid-20th century by engineers at Bell labs.

  11. HYDROGEN BONDING IN POLYMERIC ADSORBENTS BASED ADSORPTION AND SEPARATION

    Institute of Scientific and Technical Information of China (English)

    XUMancai; SHIZuoqing; 等

    2000-01-01

    After a concise introduction of hydrogen bonding effects in solute-solute and solute-solvent bonding,the design of polymeric adsorbents based on hydrogen bonding ,selectivity in adsorption through hydrogen bonding,and characterization of hydrogen bonding in adsorption and separation were reviewed with 28 references.

  12. Low Pressure Adsorbent for Recovery & Storage Vented Hydrogen Project

    Data.gov (United States)

    National Aeronautics and Space Administration — A high performance fullerene-based adsorbent is proposed for recovery and storage hydrogen and separating helium via pressure-swing-adsorption (PSA) process....

  13. Hydrogen molecule on lithium adsorbed graphene: A DFT study

    Science.gov (United States)

    Kaur, Gagandeep; Gupta, Shuchi; Gaganpreet, Dharamvir, Keya

    2016-05-01

    Electronic structure calculations for the adsorption of molecular hydrogen on lithium (Li) decorated and pristine graphene have been studied systematically using SIESTA code [1] within the framework of the first-principle DFT under the Perdew-Burke-Ernzerhof (PBE) form of the generalized gradient approximation (GGA)[2], including spin polarization. The energy of adsorption of hydrogen molecule on graphene is always enhanced by the presence of co-adsorbed lithium. The most efficient adsorption configuration is when H2 is lying parallel to lithium adsorbed graphene which is in contrast to its adsorption on pristine graphene (PG) where it prefers perpendicular orientation.

  14. Precision Spectroscopy of Atomic Hydrogen

    Science.gov (United States)

    Beyer, A.; Parthey, Ch G.; Kolachevsky, N.; Alnis, J.; Khabarova, K.; Pohl, R.; Peters, E.; Yost, D. C.; Matveev, A.; Predehl, K.; Droste, S.; Wilken, T.; Holzwarth, R.; Hänsch, T. W.; Abgrall, M.; Rovera, D.; Salomon, Ch; Laurent, Ph; Udem, Th

    2013-12-01

    Precise determinations of transition frequencies of simple atomic systems are required for a number of fundamental applications such as tests of quantum electrodynamics (QED), the determination of fundamental constants and nuclear charge radii. The sharpest transition in atomic hydrogen occurs between the metastable 2S state and the 1S ground state. Its transition frequency has now been measured with almost 15 digits accuracy using an optical frequency comb and a cesium atomic clock as a reference [1]. A recent measurement of the 2S - 2P3/2 transition frequency in muonic hydrogen is in significant contradiction to the hydrogen data if QED calculations are assumed to be correct [2, 3]. We hope to contribute to this so-called "proton size puzzle" by providing additional experimental input from hydrogen spectroscopy.

  15. A polarized atomic hydrogen beam

    OpenAIRE

    Chan, N; Crowe, D.M.; Lubell, M. S.; Tang, F.C.; Vasilakis, A.; Mulligan, F. J.; Slevin, J.

    1988-01-01

    We describe the design and operating characteristics of a simple polarized atomic hydrogen beam particularly suitable for applications to crossed beams experiments. In addition to experimental measurements, we present the results of detailed computer models, using Monte-Carlo ray tracing techniques, optical analogs, and phase-space methods, that not only provide us with a confirmation of our measurement, but also allow us to characterize the density, polarization, and atomic fraction of the b...

  16. Metal loaded zeolite adsorbents for hydrogen cyanide removal

    Institute of Scientific and Technical Information of China (English)

    Ping Ning; Juan Qiu; Xueqian Wang; Wei Liu; Wei Chen

    2013-01-01

    Metal (Cu,Co,or Zn) loaded ZSM-5 and Y zeolite adsorbents were prepared for the adsorption of hydrogen cyanide (HCN) toxic gas.The results showed that the HCN breakthrough capacity was enhanced significantly when zeolites were loaded with Cu.The physical and chemical properties of the adsorbents that influence the HCN adsorption capacity were analyzed.The maximal HCN breakthrough capacities were about the same for both zeolites at 2.2 mol of HCN/mol of Cu.The Cu2p XPS spectra showed that the possible species present were Cu2O and CuO.The N1s XPS data and FT-IR spectra indicated that CN-would be formed in the presence of Cu+/Cu2+and oxygen gas,and the reaction product could be adsorbed onto Cu/ZSM-5 zeolite more easily than HCN.

  17. Hydrogen atom donors: recent developments.

    Science.gov (United States)

    Gansäuer, Andreas; Shi, Lei; Otte, Matthias; Huth, Inga; Rosales, Antonio; Sancho-Sanz, Iris; Padial, Natalia M; Oltra, J Enrique

    2012-01-01

    This review highlights recent developments in the field of hydrogen atom transfer (HAT) reagents that circumvent the disadvantages of classical group 14 reagents, such as Bu₃SnH. Special emphasis is laid on the lowering of bond dissociation energies (BDEs) of molecules that could, as yet, not be used as HAT reagents and on the use of organometallic HAT reagents. PMID:21452081

  18. A polarized atomic hydrogen beam

    International Nuclear Information System (INIS)

    We describe the design and operating characteristics of a simple polarized atomic hydrogen beam particularly suitable for applications to crossed beams experiments. In addition to experimental measurements, we present the results of detailed computer models, using Monte-Carlo ray tracing techniques, optical analogs, and phase-space methods, that not only provide us with a confirmation of our measurement, but also allow us to characterize the density, polarization, and atomic fraction of the beam at all points along its path. As a subsidiary result, we also present measurements of the relative and absolute efficiencies of the V/G Supavac mass analyzer for masses 1 and 2. (orig.)

  19. A theoretical study of the interaction of hydrogen and oxygen with palladium or gold adsorbed on pyridine-like nitrogen-doped graphene.

    Science.gov (United States)

    Rangel, Eduardo; Magana, Luis Fernando; Sansores, Luis Enrique

    2014-12-15

    The interaction of H2 and O2 molecules in the presence of nitrogen-doped graphene decorated with either a palladium or gold atom was investigated by using density functional theory. It was found that two hydrogen molecules were adsorbed on the palladium atom. The interaction of these adsorbed hydrogen molecules with two oxygen molecules generates two hydrogen peroxide molecules first through a Eley-Rideal mechanism and then through a Langmuir-Hinshelwood mechanism. The barrier energies for this reaction were small; therefore, we expect that this process may occur spontaneously at room temperature. In the case of gold, a single hydrogen molecule is adsorbed and dissociated on the metal atom. The interaction of the dissociated hydrogen molecule on the surface with one oxygen molecule generates a water molecule. The competitive adsorption between oxygen and hydrogen molecules slightly favors oxygen adsorption.

  20. Characterizing rate inhibition in steam/hydrogen gasification via analysis of adsorbed hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Lussier, M.G.; Zhang, Z.; Miller, D.J. [Michigan State University, East Lansing, MI (United States). Dept. of Chemical Engineering

    1998-12-31

    The paper studied the analysis of hydrogen adsorbed onto Saran and coal char conducted via post-gasification temperature programmed desorption to 1770 K to characterize hydrogen inhibition in steam gasification. Exposure of annealed, outgassed chars to H{sub 2}O/H{sub 2}/Ar mixtures at 1120 K and pressures to 3.1 MPa results in rapid adsorption of hydrogen on the char over the initial 0.5% of char conversion. Steam gasification rate simultaneously declines as a result of adsorbing hydrogen blocking a portion of reactive surface sites. Between 0.5 and 40% char conversion, adsorbed hydrogen concentration is constant at all conditions; steam gasification rate is also constant with conversion but depends strongly on hydrogen partial pressure through the reverse oxygen exchange pathway. Thus, dissociative adsorption is the observed mode of inhibition when quantities of hydrogen are limited, and reverse oxygen exchange dictates rate dependence on hydrogen at elevated pressures where the char surface is essentially saturated in hydrogen.

  1. Adsorbate Electric Fields on a Cryogenic Atom Chip

    CERN Document Server

    Chan, K S; Hufnagel, C; Dumke, R

    2013-01-01

    We investigate the behaviour of electric fields originating from adsorbates deposited on a cryogenic atom chip as it is cooled from room temperature to cryogenic temperature. Using Rydberg electromagnetically induced transparency we measure the field strength versus distance from a 1 mm square of YBCO patterned onto a YSZ chip substrate. We find a localized and stable dipole field at room temperature and attribute it to a saturated layer of chemically adsorbed rubidium atoms on the YBCO. As the chip is cooled towards 83 K we observe a change in sign of the electric field as well as a transition from a localized to a delocalized dipole density. We relate these changes to the onset of physisorption on the chip surface when the van der Waals attraction overcomes the thermal desorption mechanisms. Our findings suggest that, through careful selection of substrate materials, it may be possible to reduce the electric fields caused by atomic adsorption on chips, opening up experiments to controlled Rydberg-surface co...

  2. Interaction of gas phase atomic hydrogen with Pt(111): Direct evidence for the formation of bulk hydrogen species

    Institute of Scientific and Technical Information of China (English)

    JIANG ZhiQuan; HUANG WeiXin; BAO XinHe

    2007-01-01

    Employing hot tungsten filament to thermal dissociate molecular hydrogen, we generated gas phase atomic hydrogen under ultra-high vacuum (UHV) conditions and investigated its interaction with Pt(111) surface. Thermal desorption spectroscopy (TDS) results demonstrate that adsorption of molecular hydrogen on Pt(111) forms surface Had species whereas adsorption of atomic hydrogen forms not only surface Had species but also bulk Had species. Bulk Had species is more thermal-unstable than surface Had species on Pt(111), suggesting that bulk Had species is more energetic. This kind of weakly- adsorbed bulk Had species might be the active hydrogen species in the Pt-catalyzed hydrogenation reactions.

  3. Hydrogen-Atom Transfer Reactions.

    Science.gov (United States)

    Wang, Liang; Xiao, Jian

    2016-04-01

    The cascade [1,n]-hydrogen transfer/cyclization, recognized as the tert-amino effect one century ago, has received considerable interest in recent decades, and great achievements have been made. With the aid of this strategy, the inert C(sp(3))-H bonds can be directly functionalized into C-C, C-N, C-O bonds under catalysis of Lewis acids, Brønsted acids, as well as organocatalysts, and even merely under thermal conditions. Hydrogen can be transferred intramolecularly from hydrogen donor to acceptor in the form of hydride, or proton, followed by cyclization to furnish the cyclic products in processes featuring high atom economy. Methylene/methine adjacent to heteroatoms, e.g., nitrogen, oxygen, sulfur, can be exploited as hydride donor as well as methylene/methine without heteroatom assistance. Miscellaneous electrophilic subunits or intermediates, e.g., alkylidene malonate, carbophilic metal activated alkyne or allene, α,β-unsaturated aldehydes/ketone, saturated aldehydes/iminium, ketenimine/carbodiimide, metal carbenoid, electron-withdrawing groups activated allene/alkyne, in situ generated carbocation, can serve as hydride acceptors. This methodology has shown preeminent power to construct 5-, 6-, or 7-membered heterocyclic as well as carbon rings. In this chapter, various hydrogen donors and acceptors are adequately discussed. PMID:27573142

  4. Chiral modification of platinum: ab initio study of the effect of hydrogen coadsorption on stability and geometry of adsorbed cinchona alkaloids.

    Science.gov (United States)

    Hahn, Konstanze R; Seitsonen, Ari P; Baiker, Alfons

    2015-11-01

    The cinchona alkaloids cinchonidine and cinchonine belong to the most efficient chiral modifiers for the noble metal-catalyzed enantioselective hydrogenation of C=O and C=C bonds. Under reaction conditions these modifiers are coadsorbed on the noble metal surface with hydrogen. Using density functional theory, we studied the effect of coadsorbed hydrogen on the adsorption mode of cinchonidine and cinchonine on a Pt(111) surface at different hydrogen coverages. The theoretical study indicates that the presence of coadsorbed hydrogen affects both the adsorption geometry as well as the stability of the adsorbed cinchona alkaloids. At all hydrogen coverages the cinchona alkaloids are found to be adsorbed via anchoring of the quinoline moiety. In the absence of hydrogen as well as at low hydrogen coverage the quinoline moiety adsorbs nearly parallel to the surface, whereas at higher hydrogen coverage it becomes tilted. Higher hydrogen coverage as well as partial hydrogenation of the quinoline part of the cinchona alkaloid and hydrogen transfer to the C[double bond, length as m-dash]C double bond at 10, 11 position of the quinuclidine moiety destabilize the adsorbed cinchona alkaloid, whereas hydrogen transfer to the nitrogen atom of the quinoline and the quinuclidine moiety stabilizes the adsorbed molecule. The stability as well as the adsorption geometry of the cinchona alkaloids are affected by the coadsorbed hydrogen and are proposed to influence the efficiency of the enantiodifferentiating ability of the chirally modified platinum surface.

  5. Precision spectroscopy on atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Parthey, Christian Godehard

    2011-12-15

    This Thesis reports on three measurements involving the 1S-2S transition in atomic hydrogen and deuterium conducted on a 5.8 K atomic beam. The transition is excited Doppler-free via two counter-propagating photons near 243 nm. The H/D isotope shift has been determined as {delta}{integral}{sub exp}=670 994 334 606(15) Hz. Comparing with the theoretical value for the isotope shift, excluding the leading nuclear size effect, {delta}{integral}{sub th}=670 999 566.90(66)(60) kHz we confirm, twice more accurate, the rms charge radius difference of the deuteron and the proton as left angle r{sup 2} right angle {sub d}- left angle r{sup 2} right angle {sub p}=3.82007(65) fm{sup 2} and the deuteron structure radius r{sub str}=1.97507(78) fm. The frequency ratio of the 1S-2S transition in atomic hydrogen to the cesium ground state hyperfine transition provided by the mobile cesium fountain clock FOM is measured to be {integral}{sub 1S-2S}=2 466 061 413 187 035 (10) Hz which presents a fractional frequency uncertainty of 4.2 x 10{sup -15}. The second absolute frequency measurement of the 1S-2S transition in atomic hydrogen presents the first application of a 900 km fiber link between MPQ and Physikalisch- Technische Bundesanstalt (PTB) in Braunschweig which we have used to calibrate the MPQ hydrogen maser with the stationary cesium fountain clock CSF1 at PTB. With the result of {integral}{sub 1S-2S}=2 466 061 413 187 017 (11) Hz we can put a constraint on the electron Lorentz boost violating coefficients 0.95c{sub (TX)}-0.29c{sub (TY)}-0.08 c{sub (TZ)}=(2.2{+-}1.8) x 10{sup -11} within the framework of minimal standard model extensions. We limit a possible drift of the strong coupling constant through the ratio of magnetic moments at a competitive level ({partial_derivative})/({partial_derivative}t)ln ({mu}{sub Cs})/({mu}{sub B})=-(3.0{+-}1.2) x 10{sup -15} yr{sup -1}.

  6. Precision spectroscopy on atomic hydrogen

    International Nuclear Information System (INIS)

    This Thesis reports on three measurements involving the 1S-2S transition in atomic hydrogen and deuterium conducted on a 5.8 K atomic beam. The transition is excited Doppler-free via two counter-propagating photons near 243 nm. The H/D isotope shift has been determined as Δ∫exp=670 994 334 606(15) Hz. Comparing with the theoretical value for the isotope shift, excluding the leading nuclear size effect, Δ∫th=670 999 566.90(66)(60) kHz we confirm, twice more accurate, the rms charge radius difference of the deuteron and the proton as left angle r2 right angle d- left angle r2 right angle p=3.82007(65) fm2 and the deuteron structure radius rstr=1.97507(78) fm. The frequency ratio of the 1S-2S transition in atomic hydrogen to the cesium ground state hyperfine transition provided by the mobile cesium fountain clock FOM is measured to be ∫1S-2S=2 466 061 413 187 035 (10) Hz which presents a fractional frequency uncertainty of 4.2 x 10-15. The second absolute frequency measurement of the 1S-2S transition in atomic hydrogen presents the first application of a 900 km fiber link between MPQ and Physikalisch- Technische Bundesanstalt (PTB) in Braunschweig which we have used to calibrate the MPQ hydrogen maser with the stationary cesium fountain clock CSF1 at PTB. With the result of ∫1S-2S=2 466 061 413 187 017 (11) Hz we can put a constraint on the electron Lorentz boost violating coefficients 0.95c(TX)-0.29c(TY)-0.08 c(TZ)=(2.2±1.8) x 10-11 within the framework of minimal standard model extensions. We limit a possible drift of the strong coupling constant through the ratio of magnetic moments at a competitive level (∂)/(∂t)ln (μCs)/(μB)=-(3.0±1.2) x 10-15 yr-1.

  7. ADSORPTION OF CAFFEINE BY HYDROGEN DONATING ADSORBENTS BASED ON HYDROGEN BONDING

    Institute of Scientific and Technical Information of China (English)

    XUMancai; SHIZuoqing; 等

    2000-01-01

    The adsorption isotherms of caffeine from aqueous solution onto three hydrogen donating adsorbents-hydroxypolystyrene,polystryene-azo-pyrogallol,and D72 resin-were measured.The adsorption enthalpies calculated from the isotherms according to the Clausisu-Clapeyron equation were -24-36kJ/mol,-32-37kJ/mol,and -19-24kJ/mol respectively.These values implied that the adsorption processes were based on hydrogen bonding.Furthermore.the mechanism of the adsorption of caffeine onto D72 resin was studied by IR spectra and the small molecular model experiments,and the results showed that the adsorption of caffeine onto hydrogen donating adsorbents was based on hydrogen bonding.

  8. Halo Tracing with Atomic Hydrogen

    CERN Document Server

    Merrifield, M R

    2001-01-01

    This paper reviews the constraints that can be placed on the shapes of disk galaxies' dark halos using the distribution and kinematics of atomic hydrogen. These data indicate that dark halos are close to axisymmetric, with their axes of symmetry co-aligned with their disk axes. They also appear to be oblate, with shortest-to-longest axis ratios displaying quite a broad range of values from ~0.2 to ~0.8. These results are consistent with the predicted shapes of halos in cold dark matter scenarios, but rule out some of the more exotic dark matter candidates. However, the total number of measurements is still depressingly small, and more data are required if halo shape is to become a powerful diagnostic for theories of galaxy formation and evolution.

  9. Application of Henry's Law for Binding Energies of Adsorbed Hydrogen

    Science.gov (United States)

    Gillespie, Andrew; Dohnke, Elmar; Stalla, David; Sweany, Mark; Pfeifer, Peter

    2015-03-01

    The method of isosteres is the simplest method used to calculate the differential enthalpy of adsorption. However, it is incredibly sensitive to the choice of model and respective fitting parameters. For a set of isotherms measured on a specific sample, most models converge upon a similar value at high coverage, but are inconsistent in the low pressure regime. In this talk, we investigate the application of various models for localized and mobile adsorption at low pressures in order to obtain binding energy of hydrogen to the adsorbent surface. Henry's Law analysis of the Langmuir Model of adsorption yield binding energies in excellent agreement with those obtained from the Clausius Clapeyron relation. Work supported by DOE-EERE, Award No. DE-FG36-08GO18142.

  10. Studies in Composing Hydrogen Atom Wavefunctions

    DEFF Research Database (Denmark)

    Putnam, Lance Jonathan; Kuchera-Morin, JoAnn; Peliti, Luca

    2015-01-01

    We present our studies in composing elementary wavefunctions of a hydrogen-like atom and identify several relationships between physical phenomena and musical composition that helped guide the process. The hydrogen-like atom accurately describes some of the fundamental quantum mechanical phenomen...

  11. Muonium/muonic hydrogen formation in atomic hydrogen

    Indian Academy of Sciences (India)

    V S Kulhar

    2004-09-01

    The muonium/muonic hydrogen atom formation in ± –H collisions is investigated, using a two-state approximation in a time dependent formalism. It is found that muonium cross-section results are similar to the cross-section results obtained for positronium formation in + –H collision. Muonic hydrogen atom formation cross-sections in - –H collision are found to be significant in a narrow range of energy (5 eV–25 eV).

  12. A Comprehensive Study of Hydrogen Adsorbing to Amorphous Water-Ice: Defining Adsorption in Classical Molecular Dynamics

    CERN Document Server

    Dupuy, John L; Stancil, P C

    2016-01-01

    Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g. a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H$_2$) in the ISM is the prototypical example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics (MD) simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking ...

  13. Correlation effects in photoemission from adsorbates: Hydrogen on narrow-band metals

    Science.gov (United States)

    Rubio, J.; Refolio, M. C.; López Sancho, M. P.; López Sancho, J. M.

    1988-08-01

    This paper deals with photoemission from a one-level atom adsorbed on a metal surface within the context of Anderson's Hamiltonian. The occupied part of the adsorbate density of states (DOS) is calculated by means of a many-electron approach that incorporates the following ingredients: (1) A neat separation between final-state interactions and initial (ground-state) effects. (2) The method (a Lehmann-type representation) leans heavily on the resolvent operator, R(z)=(z-H)-1, which is obtained by expressing Dyson's equation in terms of the (N-1)-electron states (configurations) that diagonalize the hopping-free part of Anderson's Hamiltonian, thereby including the atomic correlation (U) in a nonperturbative way while expanding in powers of the hopping parameter (V). (3) By using blocking methods, the matrix elements of R are grouped into equivalent 4×4 matrix blocks, with residual interactions, which are then put in correspondence with the sites of a rectangular lattice, thereby making the problem isomorphic to that of finding a noninteracting one-electron Green's function in the Wannier representation. (4) Renormalized perturbation theory, along with a series of convolution theorems due to Hugenholtz and Van Hove, allows one to develop a self-consistency equation that automatically takes into account an infinite number of configurations. The resulting DOS is compared with photoemission spectra from hydrogen adsorbed on tungsten (half-filled metal band) and nickel (almost full). Correlation effects turn out to produce peaks at the appropriate energies, so that an unusually good agreement is found despite the featureless, semielliptical DOS adopted for the metal. Only gross features of this quantity, such as width, center, and occupation of the band, seem to matter in a photoemission calculation.

  14. Atomic hydrogen and fundamental physical constants

    International Nuclear Information System (INIS)

    Techniques are described which allow the study, in undergraduate laboratories, of the spectrum of atomic hydrogen. The Rydberg constant, the electron-proton mass ratio, and the fine-structure constant are evaluated from the measurements. The key to the series of experiments is a discharge tube in which atomic lines dominate over the molecular lines. (author)

  15. Atomic hydrogen interaction with Ru(1010).

    Science.gov (United States)

    Vesselli, E; Comelli, G; Rosei, R

    2004-05-01

    The interaction of atomic hydrogen with clean and deuterium precovered Ru(1010) was studied by means of temperature-programmed desorption (TPD) spectroscopy. Compared to molecular hydrogen experiments, after exposure of the clean surface to gas-phase atomic hydrogen at 90 K, two additional peaks grow in the desorption spectra at 115 and 150 K. The surface saturation coverage, determined by equilibrium between abstraction and adsorption reactions, is 2.5 monolayers. Preadsorbed deuterium abstraction experiments with gas-phase atomic hydrogen show that a pure Eley-Rideal mechanism is not involved in the process, while a hot atom (HA) kinetics describes well the reaction. By least-squares fitting of the experimental data, a simplified HA kinetic model yields an abstraction cross section value of 0.5 +/- 0.2 angstroms2. The atomic hydrogen interaction with an oxygen precovered surface was also studied by means of both TPD and x-ray photoelectron spectroscopy: oxygen hydrogenation and water production take place already at very low temperature (90 K).

  16. On the energy of electric field in hydrogen atom

    OpenAIRE

    Kornyushin, Yuri

    2009-01-01

    It is shown that hydrogen atom is a unique object in physics having negative energy of electric field, which is present in the atom. This refers also to some hydrogen-type atoms: hydrogen anti-atom, atom composed of proton and antiproton, and positronium.

  17. Software for Hydrogenic Atoms and Orbitals Visualization

    Directory of Open Access Journals (Sweden)

    Kowit KITTIWUTTHISAKDI

    2005-06-01

    Full Text Available A program was developed in java for hydrogenic atoms and orbitals visualization. The first 18 atoms in the periodic table were approximated with a hydrogenic wave-function. This simple hydrogenic wave-function allowed quick calculation for real-time interactive visualization. Electron cloud based models were employed and displayed by a ray-tracing technique. One or more orbitals that defined an atom could be selected and displayed. A user could zoom in, zoom out, and rotate the displayed cloud in real time. The approximation method for probability integrals was summation. The intensity of color at each point on the screen directly related to the integrated probability in finding the electron across the viewer%s eye path.

  18. Positron impact ionization of atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Jones, G.O.; Charlton, M.; Slevin, J.; Laricchia, G.; Kover, A.; Poulsen, M.R.; Chormaic, S.N. (University Coll., London (United Kingdom). Dept. of Physics and Astronomy)

    1993-08-14

    Ionization cross sections for positrons impacting on atomic hydrogen have been measured for kinetic energies in the range 15-700 eV. This has been done in a crossed-beam geometry where a magnetically guided positron beam intersects a hydrogen gas jet emanating from a radio frequency discharge tube. Electron impact ionization cross sections were also measured with the same apparatus thus facilitating comparison with, and normalization to, published results. (author).

  19. Positron impact ionization of atomic hydrogen

    International Nuclear Information System (INIS)

    Ionization cross sections for positrons impacting on atomic hydrogen have been measured for kinetic energies in the range 15-700 eV. This has been done in a crossed-beam geometry where a magnetically guided positron beam intersects a hydrogen gas jet emanating from a radio frequency discharge tube. Electron impact ionization cross sections were also measured with the same apparatus thus facilitating comparison with, and normalization to, published results. (author)

  20. Interaction between adsorbed hydrogen and potassium on a carbon nanocone containing material as studied by photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Xiaofeng [Nesna University College, 8700 Nesna (Norway); Raaen, Steinar, E-mail: sraaen@ntnu.no [Physics Department, Norwegian University of Science and Technology, 7491 Trondheim (Norway)

    2015-09-14

    Hydrogen adsorption on a potassium doped carbon nanocone containing material was studied by photoelectron spectroscopy and work function measurement. The valence band spectra indicate that there is charge transfer from potassium to carbon. Upon deposition on carbon potassium is in its ionic state for lower doping and shows both ionic and metallic behavior at higher doping. Adsorption of hydrogen facilitates diffusion of potassium on the carbon material as seen by changes in the K{sub 2p} core level spectrum. Variations in the measured sample work function indicate that hydrogen initially adsorb on the K dopants and subsequently adsorb on the carbon cone containing material.

  1. Interaction of gas phase atomic hydrogen with Pt(111):Direct evidence for the formation of bulk hydrogen species

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Employing hot tungsten filament to thermal dissociate molecular hydrogen,we generated gas phase atomic hydrogen under ultra-high vacuum(UHV)conditions and investigated its interaction with Pt(111) surface.Thermal desorption spectroscopy(TDS)results demonstrate that adsorption of molecular hy- drogen on Pt(111)forms surface Had species whereas adsorption of atomic hydrogen forms not only surface Had species but also bulk Had species.Bulk Had species is more thermal-unstable than surface Had species on Pt(111),suggesting that bulk Had species is more energetic.This kind of weakly- adsorbed bulk Had species might be the active hydrogen species in the Pt-catalyzed hydrogenation reactions.

  2. Adsorbed hydrogen detection on a surface by slow electron energy loss, physisorption, chemisorption

    International Nuclear Information System (INIS)

    The use of Electron Energy Loss Spectroscopy (EELS) for the detection of hydrogen adsorbed on a surface is discussed. The principle of EELS is reminded and the experimental set up described. An overwiew of experimental results obtained on various substrates is given. It is shown that this method is able to determine the chemical form of hydrogen (physisorbed, chemisorbed, etc...). Furthermore the role of the surface dipole moment on hydrogen physisorption is outlined

  3. Radiation of partially ionized atomic hydrogen

    Science.gov (United States)

    Soon, W. H.; Kunc, J. A.

    1990-01-01

    A nonlinear collisional-radiative model for determination of production of electrons, positive and negative ions, excited atoms, and spectral and continuum line intensities in stationary partially ionized atomic hydrogen is presented. Transport of radiation is included by coupling the rate equations for production of the electrons, ions, and excited atoms with the radiation escape factors, which are not constant but depend on plasma conditions. It is found that the contribution of the negative ion emission to the total continuum emission can be important. Comparison of the calculated total continuum emission coefficient, including the negative ion emission, is in good agreement with experimental results.

  4. Radio frequency atomic hydrogen beam source

    International Nuclear Information System (INIS)

    A simple, convenient rf discharge source for the production of an intense beam of hydrogen atoms is described. The design and operation is such that the discharge tube can be operated over a period of several thousand hours, producing an intense beam with dissociation approx.95%

  5. Hydrogen Atom Spectrum in Noncommutative Phase Space

    Institute of Scientific and Technical Information of China (English)

    LI Kang; CHAMOUN Nidal

    2006-01-01

    @@ We study the energy levels of the hydrogen atom in the noncommutative phase space with simultaneous spacespace and momentum-momentum noncommutative relations. We find new terms compared to the case that only noncommutative space-space relations are assumed. We also present some comments on a previous paper [Alavi S A hep-th/0501215].

  6. From lattice gauge theories to hydrogen atoms

    Directory of Open Access Journals (Sweden)

    Manu Mathur

    2015-10-01

    Full Text Available We construct canonical transformations to obtain a complete and most economical realization of the physical Hilbert space Hp of pure SU(22+1 lattice gauge theory in terms of Wigner coupled Hilbert spaces of hydrogen atoms. One hydrogen atom is assigned to every plaquette of the lattice. A complete orthonormal description of the Wilson loop basis in Hp is obtained by all possible angular momentum Wigner couplings of hydrogen atom energy eigenstates |n l m〉 describing electric fluxes on the loops. The SU(2 gauge invariance implies that the total angular momenta of all hydrogen atoms vanish. The canonical transformations also enable us to rewrite the Kogut–Susskind Hamiltonian in terms of fundamental Wilson loop operators and their conjugate electric fields. The resulting loop Hamiltonian has a global SU(2 invariance and a simple weak coupling (g2→0 continuum limit. The canonical transformations leading to the loop Hamiltonian are valid for any SU(N. The ideas and techniques can also be extended to higher dimension.

  7. Molecular beam studies of oxide reduction by atomic hydrogen

    International Nuclear Information System (INIS)

    The graphite and oxide internals of a CTR are susceptible to chemical corrosion as well as to physical degradation by high-energy particles. Reactions of thermal atomic hydrogen with oxides are being studied. The hydrogen used is at thermal energy (0.22 eV). Typical data are reported for the H/UO2 system. The reaction probability is plotted as a function of solid temperature at fixed beam intensity and moculation frequency. The reaction probability increases from low temperature to a high-temperature plateau at about 13000C. Here the reaction rate is limited solely by the sticking probability of H on the surface; about one in seven of the incident atoms is chemisorbed by the surface and ultimately returns to the gas phase as water vapor. A reaction model comprising sticking, recombination to H2, solution and diffusion of H in the bulk of the UO2, surface reaction of adsorbed H with lattice oxygen atoms to produce the hydroxyl radical, and production of water is constructed. The rate constants for the elementary steps in the mechanism are tabulated. 2 figures, 2 tables

  8. Adsorption of cyclic hydrocarbons on Pt and the interaction of the adsorbed species with hydrogen

    International Nuclear Information System (INIS)

    The adsorption of six-membered hydrocarbon cycles and cyclopentane and the interaction of hydrogen with the adsorbed layer on polycrystalline Pt-foil have been studied. The work function change (Δφ) was followed by a Kelvin probe and the C/Pt peak ratio was determined by Auger electron spectroscopy. Combining these two techniques made it possible to distinguish between chemisorption via σ-bonds and π-complex formation. Benzene and toluene adsorbed first as π-complex while cyclohexane showed initially a partial aromatization and a π-complex-like bonding to the surface. Excess hydrocarbon or addition of hydrogen transformed the π-complex into σ-bonded species. Cyclopentane adsorbed via σ-bonds and showed no significant hydrogen effect

  9. Interaction of a slow monopole with a hydrogen atom

    OpenAIRE

    Shnir, Ya. M.

    1996-01-01

    The electric dipole moment of the hydrogen-like atom induced by a monopole moving outside the electron shell is calculated. The correction to the energy of the ground state of the hydrogen atom due to this interaction is calculated.

  10. Model study in chemisorption: atomic hydrogen on beryllium clusters

    Energy Technology Data Exchange (ETDEWEB)

    Bauschlicher, C.W. Jr.

    1976-08-01

    The interaction between atomic hydrogen and the (0001) surface of Be metal has been studied by ab initio electronic structure theory. Self-consistent-field (SCF) calculations have been performed using minimum, optimized minimum, double zeta and mixed basis sets for clusters as large as 22 Be atoms. The binding energy and equilibrium geometry (the distance to the surface) were determined for 4 sites. Both spatially restricted (the wavefunction was constrained to transform as one of the irreducible representations of the molecular point group) and unrestricted SCF calculations were performed. Using only the optimized minimum basis set, clusters containing as many as 22 beryllium atoms have been investigated. From a variety of considerations, this cluster is seen to be nearly converged within the model used, providing the most reliable results for chemisorption. The site dependence of the frequency is shown to be a geometrical effect depending on the number and angle of the bonds. The diffusion of atomic hydrogen through a perfect beryllium crystal is predicted to be energetically unfavorable. The cohesive energy, the ionization energy and the singlet-triplet separation were computed for the clusters without hydrogen. These quantities can be seen as a measure of the total amount of edge effects. The chemisorptive properties are not related to the total amount of edge effects, but rather the edge effects felt by the adsorbate bonding berylliums. This lack of correlation with the total edge effects illustrates the local nature of the bonding, further strengthening the cluster model for chemisorption. A detailed discussion of the bonding and electronic structure is included. The remaining edge effects for the Be/sub 22/ cluster are discussed.

  11. Study on hydrogen atom adsorption and diffusion properties on Mg (0001) surface

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional theory. The calculation results of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively, Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (EF)) at Fermi level and more bonding elec- trons at the energy range blow the Fermi level of H/Mg (0001) system as compared with that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving the surface activity of Mg (0001) surface.

  12. Study on hydrogen atom adsorption and diffusion properties on Mg (0001) surface

    Institute of Scientific and Technical Information of China (English)

    ZHANG dian; ZHOU DianWu; LIU dinShui

    2009-01-01

    Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional theory. The calculation results of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects,which affect hydrogen diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively, Mg atom vacancy on Mg(0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (EF)) at Fermi level and more bonding electrons at the energy range blow the Fermi level of H/Mg (0001) system as compared with that at hcp site.On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving the surface activity of Mg (0001) surface.

  13. Hydrogen atom in a Laser-Plasma

    CERN Document Server

    Falaye, Babatunde James; Liman, Muhammed S; Oyewumi, K J; Dong, Shi-Hai

    2016-01-01

    We scrutinize the behaviour of hydrogen atom's eigenvalues in a quantum plasma as it interacts with electric field directed along $\\theta=\\pi$ and exposed to linearly polarized intense laser field radiation. Using the Kramers-Henneberger (KH) unitary transformation, which is semiclassical counterpart of the Block-Nordsieck transformation in the quantized field formalism, the squared vector potential that appears in the equation of motion is eliminated and the resultant equation is expressed in KH frame. Within this frame, the resulting potential and the corresponding wavefunction have been expanded in Fourier series and using Ehlotzky's approximation, we obtain a laser-dressed potential to simulate intense laser field. By fitting the exponential-cosine-screened Coulomb potential into the laser-dressed potential, and then expanding it in Taylor series up to $\\mathcal{O}(r^4,\\alpha_0^9)$, we obtain the eigensolution (eigenvalues and wavefunction) of hydrogen atom in laser-plasma encircled by electric field, wit...

  14. Atomic hydrogen in a magnetic trap

    International Nuclear Information System (INIS)

    This thesis describes the construction and application of a static magnetic trap for atomic hydrogen. It is demonstrated that densities of up to 3*1014 cm-3 at temperatures of 80 to 200 mK can be achieved with a technically simple method of filling the trap. Double polarization is shown to occur spontaneously in the trapped gas, and the dipolar relaxation rate and its field dependance are measured confirming theoretical predictions. These results show that atomic hydrogen is a promising material for the achievement of Bose-Einstein condensation, provided that apart from the present method of cooling the gas, which is shown to impose a lower limit on the temperature, another cooling mechanism is supplied to reach lower temperatures. The density reached was two orders of magnitude higher than that of trapping experiments done at MIT where the technique of evaporate cooling was used to reach a temperature lower than 3 mK. (author). 138 refs.; 27 figs

  15. Semiclassical treatment of laser excitation of the hydrogen atom

    DEFF Research Database (Denmark)

    Billing, Gert D.; Henriksen, Niels Engholm; Leforestier, C.

    1992-01-01

    We present an alternative method for studying excitation of atoms in intense laser fields. In the present paper we focus upon the optical harmonic generation by hydrogen atoms.......We present an alternative method for studying excitation of atoms in intense laser fields. In the present paper we focus upon the optical harmonic generation by hydrogen atoms....

  16. Classical theory of the hydrogen atom

    CERN Document Server

    Rashkovskiy, Sergey

    2016-01-01

    It is shown that all of the basic properties of the hydrogen atom can be consistently described in terms of classical electrodynamics instead of taking the electron to be a particle; we consider an electrically charged classical wave field, an "electron wave", which is held in a limited region of space by the electrostatic field of the proton. It is shown that quantum mechanics must be considered to be not a theory of particles but a classical field theory in the spirit of classical electrodynamics. In this case, we are not faced with difficulties in interpreting the results of the theory. In the framework of classical electrodynamics, all of the well-known regularities of the spontaneous emission of the hydrogen atom are obtained, which is usually derived in the framework of quantum electrodynamics. It is shown that there are no discrete states and discrete energy levels of the atom: the energy of the atom and its states change continuously. An explanation of the conventional corpuscular-statistical interpre...

  17. Modification of the electronic properties of Au/molecule/Pd junctions by adsorbed hydrogen: a DFT study

    Energy Technology Data Exchange (ETDEWEB)

    Kucera, Jan; Gross, Axel [Institut fuer Theoretische Chemie, Universitaet Ulm, D-89069 Ulm (Germany)

    2011-07-01

    Metal-molecule-metal contacts assembled from a Pd monolayer deposited on a Au-supported self-assembled monolayer (SAM) of 4-mercaptopyridine or 4-aminothiophenol were recently achieved by means of an electrochemical approach. Subsequent photoelectron spectroscopy showed a strongly reduced Pd density of states (DOS) at the Fermi energy. This phenomenon is still not fully comprehended, however, its understanding is crucial for the use of the sandwich design as a platform for future nanoelectronics. Periodic density functional theory (DFT) calculation revealed that the dehydrogenation of the amino group and the subsequent strong bonding of the remaining nitrogen atom to the Pd layer could explain the observed modification of the DOS. We have now extended this study in order to clarify the role of hydrogen atoms for the electronic properties of the Pd layers. In equilibrium, these layers should always show a considerable hydrogen coverage in an aqueous environment. Our calculations demonstrate that indeed the adsorbed hydrogen atoms significantly modify the electronic structure of the Pd layers.

  18. Radiation of partially ionized atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Soon, W.H.; Kunc, J.A. (Departments of Aerospace Engineering and Physics, University of Southern California, Los Angeles, California 90089-1191 (USA))

    1990-11-01

    A nonlinear collisional-radiative model for determination of production of electrons, positive and negative ions, excited atoms, and spectral and continuum line intensities in stationary partially ionized atomic hydrogen is presented (11 000 K{le}{ital T}{sub {ital e}}{le}15 000 K, 10{sup 10} cm{sup {minus}3}{le}{ital N}{sub {ital t}} {le}10{sup 18} cm{sup {minus}3}). Transport of radiation is included by coupling the rate equations for production of the electrons, ions, and excited atoms with the radiation escape factors, which are not constant but depend on plasma conditions. It is found that the contribution of the negative ion emission to the total continuum emission can be important. Comparison of the calculated total continuum emission coefficient, including the negative ion emission, is in good agreement with experimental results.

  19. Field-emission spectroscopy of beryllium atoms adsorbed on tungsten

    Energy Technology Data Exchange (ETDEWEB)

    Czyzewski, J.J.; Grzesiak, W.; Krajniak, J. (Politechnika Wroclawska (Poland))

    1981-01-01

    Field emission energy distributions (FEED) have been measured for the beryllium-tungsten (023) adsorption system over the 78-450 K temperature range. A temperature dependence of the normalized half-width, ..delta../d, of FEED peaks changed significantly due to beryllium adsorption; and the curve, ..delta../d vs p, for the Be/W adsorption system was identical in character to the calculated curve based on the free electron model in contrast to the curve for the clean tungsten surface. In the last part of this paper Gadzuk's theory of the resonance-tunneling effect is applied to the beryllium atom on tungsten. Experimental and theoretical curves of the enhancement factor as a function of energy have been discussed.

  20. Angular Distribution of Electrons in Photoionization of Atoms Adsorbed on a Graphene Sheet

    CERN Document Server

    Baltenkov, A S

    2013-01-01

    Within the framework of a model representing the potential of a graphene sheet U(z) as an electro-neutral layer formed by smeared carbon atoms, the effect of this potential on spectral characteristics of atoms adsorbed on a graphene sheet has been studied. Since the distance between the adsorbed atom nucleus and sheet surface significantly exceeds the radii of inner atomic shells the potential U(z) makes influence on the continuum wave functions only. Their behavior in the upper semi-space (z>0) and in the lower one (z<0) where the adsorbed atom is located is defined by a jump of the logarithmic derivative of the wave function for z=0. The photoelectron angular distributions have been calculated for different mutual positions of the polarization vector e and the axis Z normal to the sheet surface. It has been shown that the existence of the electron waves reflected from the potential U(z) leads to evident asymmetry of the angular distribution relative to the plane z=0. The experimental observation of this ...

  1. Wave mechanics of the hydrogen atom

    CERN Document Server

    Ogilvie, J F

    2016-01-01

    The hydrogen atom is a system amenable to an exact treatment within Schroedinger's formulation of quantum mechanics according to coordinates in four systems -- spherical polar, paraboloidal, ellipsoidal and spheroconical coordinates; the latter solution is reported for the first time. Applications of these solutions include angular momenta, a quantitative calculation of the absorption spectrum and accurate plots of surfaces of amplitude functions. The shape of an amplitude function, and even the quantum numbers in a particular set to specify such an individual function, depend on the coordinates in a particular chosen system, and are therefore artefacts of that particular coordinate representation within wave mechanics. All discussion of atomic or molecular properties based on such shapes or quantum numbers therefore lacks general significance

  2. Hydrogen atoms in a strong magnetic field

    International Nuclear Information System (INIS)

    The energies and wave functions of the 14 lowest states of a Hydrogen atom in a strong magnetic field are calculated, using a variational scheme. The equivalence between the atomic problem and the problems related with excitons and impurities in semiconductors in the presence of a strong magnetic field are shown. The calculations of the energies and wave functions have been divided in two regions: the first, for the magnetic field ranging between zero and 109G; in the second the magnetic field ranges between 109 and 1011G. The results have been compared with those obtained by previous authors. The computation time necessary for the calculations is small. Therefore this is a convenient scheme to obtain the energies and wave functions for the problem. Transition probabilities, wavelengths and oscillator strengths for some allowed transitions are also calculated. (Author)

  3. Research with a cold atomic hydrogen maser

    International Nuclear Information System (INIS)

    The frequency stability of the hydrogen maser is limited by thermal noise within the atomic line-width and by additive noise at the receiver. By lowering the maser's temperature its stability can be improved both through reduced thermal noise and more favorable kinetic effects in the storage process. Predicted values of the fractional frequency stability are in the range of 10 to the -17th to 10 to the -18th power for averaging intervals of 100 to 1000 seconds. The wall shift and atomic line of an oscillating maser have been measured at temperatures of 77 to 25 K. Below 50 K this was accomplished by coating the storage bulb with tetrafluoromethane (CF4) applied through the dissociator. The results of these experiments are presented and directions for future research are discussed

  4. Transport properties of zigzag graphene nanoribbons adsorbed with single iron atom

    Institute of Scientific and Technical Information of China (English)

    杨玉娥; 肖杨; 颜晓红; 戴昌杰

    2015-01-01

    We have performed density-functional calculations of the transport properties of the zigzag graphene nanoribbon (ZGNR) adsorbed with a single iron atom. Two adsorption configurations are considered, i.e., iron adsorbed on the edge and on the interior of the nanoribbon. The results show that the transport features of the two configurations are similar. However, the transport properties are modified due to the scattering effects induced by coupling of the ZGNR band states to the localized 3d-orbital state of the iron atom. More importantly, one can find that several dips appear in the transmission curve, which is closely related to the above mentioned coupling. We expect that our results will have potential applications in graphene-based spintronic devices.

  5. DEVELOPMENT OF ADSORBENTS FOR THE CAPTURE AND STORAGE OF HYDROGEN AND CARBON DIOXIDE BY MAGNETRON SPUTTERING

    OpenAIRE

    Roberts, Christopher

    2013-01-01

    Concerns about climate change have rejuvenated global efforts in reducing carbon dioxide (CO2) emissions. Tactics include capture and sequestration of CO2 from point sources and the promotion of hydrogen (H2) as a “transport fuel”. Current H2 vehicles use high pressure H2 tanks which lack the convenience of their fossil fuel counterparts and present potential safety hazards. Development of adsorbent materials that reduce the energetic costs of H2 and CO2 capture, facilitatin...

  6. Measurement of the absolute separation for atomic force microscopy measurements in the presence of adsorbed polymer

    OpenAIRE

    McKee, C. T.; Mosse, W. K. J.; Ducker, W. A.

    2006-01-01

    We demonstrate that the absolute separation between an atomic force microscope (AFM) tip and a solid substrate can be measured in the presence of an irreversibly adsorbed polymer film. The separation is obtained from the analysis of a scattered evanescent wave that is generated at the surface of the solid. By comparing our scattering measurements to conventional AFM measurements, we also show an example where a conventional AFM measurement gives the incorrect force-distance profile. We valida...

  7. Neutral-atom scattering from random isolated adsorbate atoms on clean metal surfaces: Oxygen and carbon monoxide on nickel (001)

    International Nuclear Information System (INIS)

    The intensity I of the specular beam of a helium nozzle beam scattered from a Ni(001) surface has been measured as a function of adsorbate coverage CTHETA for both oxygen and CO exposures at 350 K for different angles of incidence. A linear relationship is found between ln (I/I0) (I0, the intensity of the specular beam from the clean surface) and CTHETA up to CTHETA = 0.15 monolayer of O on Ni and CTHETA = 0.1 monolayer of CO on Ni. A model is proposed in which the scattering is governed by the repulsive part of the gas-surface potential, the latter being described by a hard-wall corrugation. A constant attractive well depth and a temperature-dependent vibration amplitude of the atoms are also incorporated into the model. The adsorbate atoms are treated as a shot noise on a flat metal surface. By means of suitable averaging, a formula is found that explains the linear dependence indicated. From the best fit of the model to the experimental data, a set of parameters describing the corrugation of a single adsorbate is derived. Cross sections for the helium-adatom scattering are 65 and 26 A2 for CO and O, respectively. The corresponding corrugations have been fitted with Gaussians of height 0.62 A (for CO) and 0.32 A (for O)

  8. Chemisorption of hydrogen and oxygen atoms on a cobalt surface: A quantum chemical cluster model study

    International Nuclear Information System (INIS)

    The chemisorption of atomic hydrogen and oxygen on a cobalt surface has been studied on a five-atom cluster model using one-electron effective core potential (le- ECP) and all-electron calculations at the ab initio SCF and MCPF levels. Also, density functional calculations have been carried out. The different approaches are evaluated. The le- ECP has been compared to similar ECPS for nickel and copper. Our results indicate that this approach is valid also for cobalt. Different contributions to the cluster-adsorbate bonding energy are discussed. 31 refs., 1 fig., 1 tab

  9. Sequential desorption energy of hydrogen from nickel clusters

    Energy Technology Data Exchange (ETDEWEB)

    Deepika,; Kumar, Rakesh, E-mail: rakesh@iitrpr.ac.in [Department of Physics, Indian Institute of Technology Ropar, Rupnagar-140001 (India); R, Kamal Raj. [Indian Institute of Science Education and Research Kolkata, Mohanpur-741246 (India); Kumar, T. J. Dhilip [Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar-140001 (India)

    2015-06-24

    We report reversible Hydrogen adsorption on Nickel clusters, which act as a catalyst for solid state storage of Hydrogen on a substrate. First-principles technique is employed to investigate the maximum number of chemically adsorbed Hydrogen molecules on Nickel cluster. We observe a maximum of four Hydrogen molecules adsorbed per Nickel atom, but the average Hydrogen molecules adsorbed per Nickel atom decrease with cluster size. The dissociative chemisorption energy per Hydrogen molecule and sequential desorption energy per Hydrogen atom on Nickel cluster is found to decrease with number of adsorbed Hydrogen molecules, which on optimization may help in economical storage and regeneration of Hydrogen as a clean energy carrier.

  10. Relativistic dynamical polarizability of hydrogen-like atoms

    International Nuclear Information System (INIS)

    Using the operator representation of the Dirac Coulomb Green function the analytical method in perturbation theory is employed in obtaining solutions of the Dirac equation for a hydrogen-like atom in a time-dependent electric field. The relativistic dynamical polarizability of hydrogen-like atoms is calculated and analysed. (Author)

  11. Convergent variational calculation of positronium-hydrogen-atom scattering lengths

    CERN Document Server

    Adhikari, S K; Adhikari, Sadhan K.; Mandal, Puspajit

    2001-01-01

    We present a convergent variational basis-set calculational scheme for elastic scattering of positronium atom by hydrogen atom in S wave. Highly correlated trial functions with appropriate symmetry are needed for achieving convergence. We report convergent results for scattering lengths in atomic units for both singlet ($=3.49\\pm 0.20$) and triplet ($=2.46\\pm 0.10$) states.

  12. Organic silicon compounds anf hydrogen sulfide removal from biogas by mineral and adsorbent

    Science.gov (United States)

    Choi, J.

    2015-12-01

    Biogas utilized for energy production needs to be free from organic silicon compounds and hydrogen sulfide , as their burning has damaging effects on utilities and humans; organic silicon compounds and hydrogen sulfide can be found in biogas produced from biomass wastes, due to their massive industrial use in synthetic product,such as cosmetics, detergents and paints.Siloxanes and hydrogen sulfide removal from biogas can be carried out by various methods (Ajhar et al., 2010); aim of the present work is to find a single practical andeconomic way to drastically and simultaneously reduce both hydrogen sulfide and the siloxanes concentration to less than 1 ppm. Some commercial activated carbons previously selected (Monteleoneet al., 2011) as being effective in hydrogen sulfide up taking have been tested in an adsorption measurement apparatus, by flowing both hydrogen sulphide and volatile siloxane (Decamethycyclopentasiloxane or D5) in a nitrogen stream,typically 25-300 ppm D5 over N2, through an clay minerals, Fe oxides and Silica; the adsorption process was analyzed by varying some experimental parameters (concentration, grain size, bed height). The best silica shows an adsorption capacity of 0.2 g D5 per gram of silica. The next thermo gravimetric analysis (TGA) confirms the capacity data obtained experimentally by the breakthrough curve tests.The capacity results depend on D5 and hydrogen sulphide concentrations. A regenerative silica process is then carried out byheating the silica bed up to 200 ° C and flushing out the adsorbed D5 and hydrogen sulphide samples in a nitrogen stream in athree step heating procedure up to 200 ° C. The adsorption capacity is observed to degrade after cyclingthe samples through several adsorption-desorption cycles.

  13. Hirshfeld atom refinement for modelling strong hydrogen bonds.

    Science.gov (United States)

    Woińska, Magdalena; Jayatilaka, Dylan; Spackman, Mark A; Edwards, Alison J; Dominiak, Paulina M; Woźniak, Krzysztof; Nishibori, Eiji; Sugimoto, Kunihisa; Grabowsky, Simon

    2014-09-01

    High-resolution low-temperature synchrotron X-ray diffraction data of the salt L-phenylalaninium hydrogen maleate are used to test the new automated iterative Hirshfeld atom refinement (HAR) procedure for the modelling of strong hydrogen bonds. The HAR models used present the first examples of Z' > 1 treatments in the framework of wavefunction-based refinement methods. L-Phenylalaninium hydrogen maleate exhibits several hydrogen bonds in its crystal structure, of which the shortest and the most challenging to model is the O-H...O intramolecular hydrogen bond present in the hydrogen maleate anion (O...O distance is about 2.41 Å). In particular, the reconstruction of the electron density in the hydrogen maleate moiety and the determination of hydrogen-atom properties [positions, bond distances and anisotropic displacement parameters (ADPs)] are the focus of the study. For comparison to the HAR results, different spherical (independent atom model, IAM) and aspherical (free multipole model, MM; transferable aspherical atom model, TAAM) X-ray refinement techniques as well as results from a low-temperature neutron-diffraction experiment are employed. Hydrogen-atom ADPs are furthermore compared to those derived from a TLS/rigid-body (SHADE) treatment of the X-ray structures. The reference neutron-diffraction experiment reveals a truly symmetric hydrogen bond in the hydrogen maleate anion. Only with HAR is it possible to freely refine hydrogen-atom positions and ADPs from the X-ray data, which leads to the best electron-density model and the closest agreement with the structural parameters derived from the neutron-diffraction experiment, e.g. the symmetric hydrogen position can be reproduced. The multipole-based refinement techniques (MM and TAAM) yield slightly asymmetric positions, whereas the IAM yields a significantly asymmetric position.

  14. Characterizing rate inhibition in H{sub 2}O/H{sub 2} gasification via measurement of adsorbed hydrogen concentration

    Energy Technology Data Exchange (ETDEWEB)

    Miller, D.J.; Lussier, M.G.; Zhang, Z. [Michigan State Univ., East Lansing, MI (United States)

    1996-10-01

    The concentration of hydrogen adsorbed on char surfaces is measured following gasification in order to characterize the mechanism and extent of hydrogen inhibition. Saran and coal chars, prepared by pyrolysis and outgassing to 1500{degrees}C, are gasified at 850{degrees}C and 0.3-3.0 MPa pressure in mixtures ranging from pure H{sub 2} to pure H{sub 2}O. Adsorbed hydrogen concentration is measured following gasification by temperature programmed desorption to 1500{degrees}C. Results show that hydrogen initially adsorbs rapidly on the char surface (up to {approximately}1% conversion) and then slowly accumulates out to 75% carbon conversion. The quantity of hydrogen adsorbed is weakly dependent on pressure or gas composition. Gasification rate initially declines rapidly and then remains constant or even increases slightly with conversion. We conclude that adsorbed hydrogen initially inhibits rate, but reverse oxygen exchange, or reduction of C(O) surface groups by gas-phase H{sub 2}, is the dominant mode of inhibition at higher extents of conversion.

  15. Effects of hydrogen atoms on surface conductivity of diamond film

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Fengbin, E-mail: fbliu@ncut.edu.cn; Cui, Yan; Qu, Min; Di, Jiejian [College of Mechanical and Electric Engineering, North China University of Technology, Beijing (China)

    2015-04-15

    To investigate the effects of surface chemisorbed hydrogen atoms and hydrogen atoms in the subsurface region of diamond on surface conductivity, models of hydrogen atoms chemisorbed on diamond with (100) orientation and various concentrations of hydrogen atoms in the subsurface layer of the diamond were built. By using the first-principles method based on density functional theory, the equilibrium geometries and densities of states of the models were studied. The results showed that the surface chemisorbed hydrogen alone could not induce high surface conductivity. In addition, isolated hydrogen atoms in the subsurface layer of the diamond prefer to exist at the bond centre site of the C-C bond. However, such a structure would induce deep localized states, which could not improve the surface conductivity. When the hydrogen concentration increases, the C-H-C-H structure and C-3H{sub bc}-C structure in the subsurface region are more stable than other configurations. The former is not beneficial to the increase of the surface conductivity. However, the latter would induce strong surface states near the Fermi level, which would give rise to high surface conductivity. Thus, a high concentration of subsurface hydrogen atoms in diamond would make significant contributions to surface conductivity.

  16. Removal of hydrogen sulfide at ambient conditions on cadmium/GO-based composite adsorbents.

    Science.gov (United States)

    Florent, Marc; Wallace, Rajiv; Bandosz, Teresa J

    2015-06-15

    Cadmium-based materials with various hydroxide to carbonate ratios and their composites with graphite oxide were synthesized by a fast and simple precipitation procedure and then used as H2S adsorbents at ambient conditions in the dark or upon a visible light exposure. The structural properties and chemical features of the adsorbents were analyzed before and after hydrogen sulfide adsorption. The results showed that the high ratio of hydroxide to carbonate led to an improved H2S adsorption capacity. In moist conditions cadmium hydroxide was the best adsorbent. Moreover, it showed photoactive properties. While the incorporation of a graphene-based phase slightly decreased the extent of the improvement in the H2S adsorption capacity in moist conditions caused by photoactivity, its presence in the composites enhanced the performance in dry conditions. This was linked to photoactivity of CdS that can split H2S resulting in the formation of water in the system. The graphene-based phase enhanced the electron transfer and delayed the recombination of photoinduced charges. Carbonate-based materials showed a very good adsorption capacity in dark conditions in the presence of moisture. Upon the light exposure, CdS likely photocatalyzes the reduction of carbonate ions to formates/formaldehydes. Their deposition on the surface limits the number of sites available to H2S adsorption. PMID:25792480

  17. Atomic hydrogen and oxygen adsorptions in single-walled zigzag silicon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Haoliang; Ray, Asok K., E-mail: akr@uta.edu [University of Texas at Arlington, Department of Physics (United States)

    2013-09-15

    Ab initio calculations have been performed to study the electronic and geometric structure properties of zigzag silicon nanotubes. Full geometry and spin optimizations have been performed without any symmetry constraints with an all electron 3-21G* basis set and the B3LYP hybrid functional. The largest zigzag SiNT studied here, (12, 0), has a binding energy per atom of 3.584 eV. Atomic hydrogen and oxygen adsorptions on (9, 0) and (10, 0) nanotubes have also been studied by optimizing the distances of the adatoms from both inside and outside the tube. The adatom is initially placed in four adsorption sites-parallel bridge (PB), zigzag bridge (ZB), hollow, and on-top site. The on-top site is the most preferred site for hydrogen atom adsorbed on (9, 0), with an adsorption energy of 3.0 eV and an optimized distance of 1.49 A from the adatom to the nearest silicon atom. For oxygen adsorption on (9, 0), the most preferred site is the ZB site, with an adsorption energy of 5.987 eV and an optimized distance of 1.72 A. For atomic hydrogen adsorption on (10, 0), the most preferred site is also the on-top site with an adsorption energy of 3.174 eV and an optimized distance of 1.49 A. For adsorption of atomic oxygen on (10, 0), the most preferred site is PB site, with an adsorption energy of 6.306 eV and an optimized distance of 1.71 A. The HOMO-LUMO gaps of (9, 0) after adsorptions of hydrogen and oxygen atoms decrease while the HOMO-LUMO gaps of (10, 0) increase after adsorption of hydrogen and oxygen.

  18. First-Principles Calculations of Scanning-Tunnelling-Microscopy Images of Ar Atoms Adsorbed on a Graphite Sheet

    Institute of Scientific and Technical Information of China (English)

    白玉林; 周晓林; 陈向荣; 芶清泉

    2003-01-01

    Local density approximation within the framework of the density functional theory is applied to calculate the scanning tunnelling microscopy(STM)images of Ar atoms adsorbed on a graphite sheet(Ar/graphite system).It is found that the optimal site of adsorbed Ar atom is at the top of the centre of the carbon hexagon and its equilibrium distance from the graphite surface is about 3.20A.We demonstrate that it is the hybridization of the C 2 p electronic states with the Ar 3 p and 4 s electronic states,which renders Ar atoms visible in the STM experiment.

  19. Quantum states of hydrogen atom on Pd(1 1 0) surface

    Science.gov (United States)

    Padama, Allan Abraham B.; Nakanishi, Hiroshi; Kasai, Hideaki

    2015-12-01

    The quantum states of adsorbed hydrogen atom on Pd(1 1 0) surface are investigated in this work. From the calculated potential energy surface (PES) of hydrogen atom on Pd(1 1 0), the wave functions and eigenenergies in the ground and few excited states of protium (H) and deuterium (D) are calculated. Localized wave functions of hydrogen atom exist on pseudo-threefold and long bridge sites of Pd(1 1 0). The short bridge site is a local minimum from the result of PES, however, quantum behavior of hydrogen revealed that its vibration would allow it to hop to other pseudo-threefold site (that crosses the short bridge site) than to stay on the short bridge site. Exchange of ordering of the wave functions between H and D is attributed to the difference in their masses. The calculated eigenenergies are found to be in fair agreement with experimental data based from the identified vibrations of hydrogen with component perpendicular to the surface. The activation barriers measured from the eigenenergies are in better agreement with experimental findings in comparison to the data gathered from PES.

  20. A new exact path integral treatment of the hydrogen atom

    International Nuclear Information System (INIS)

    Using a recently developed general new-time transformation method, free of operator ordering ambiguities by construction we reconsider the hydrogen atom problem. We solve the problem direcly without any dimension raising trick. (author)

  1. Composite systems in magnetic field: from hadrons to hydrogen atom

    OpenAIRE

    Kerbikov, B. O.

    2013-01-01

    We briefly review the recent studies of the behavior of composite systems in magnetic field. The hydrogen atom is chosen to demonstrate the new results which may be experimentally tested. Possible applications to physics of antihydrogen are mentioned.

  2. Optimization of the elaboration conditions of an adsorber for the hydrogen storage; Optimisation des conditions d'elaboration d'un adsorbant pour le stockage d'hydrogene

    Energy Technology Data Exchange (ETDEWEB)

    Fierro, V.; Mareche, J.F.; Furdin, G. [Nancy-1 Univ. Henri Poincare, UMR - CNRS 7555, Laboratoire de Chimie du Solide Mineral, 54 - Vandoeuvre-les-Nancy (France); Szczurek, A.; Albiniak, A. [Wroclaw Univ. of Technology, Laboratory for Lignites and Carbon Adsorbents, Institute of Chemistry and Technology of Petroleum and Coal (Poland); Latroche, M. [Chimie Metallurgique des Terres Rares, ICMPE, UMR 7182, CNRS, 94 - Thiais (France); Celzard, A. [Nancy-Univ., ENSTIB, Laboratoire de Chimie du Solide Mineral, UMR CNRS 7555, 88 - Epinal (France)

    2008-07-01

    The microporous carbon are very efficient adsorbents for the hydrogen storage, because of pores size under 2 nm. This study describes the optimization of the elaboration conditions for a carbon adsorbent for the hydrogen storage by adsorption. The storage capacity has been measured at 25 C for 20 MPa and also at 77 K for pressures between 6 and 9 MPa. the porous texture characterization has been realized by four molecule probes of increasing diameter: CO{sub 2}, N{sub 2}, C{sub 6}H{sub 6} and CCl{sub 4}. (A.L.B.)

  3. The mechanism of chemisorption of hydrogen atom on graphene: Insights from the reaction force and reaction electronic flux

    International Nuclear Information System (INIS)

    At the PBE-D3/cc-pVDZ level of theory, the hydrogen chemisorption on graphene was analyzed using the reaction force and reaction electronic flux (REF) theories in combination with electron population analysis. It was found that chemisorption energy barrier is mainly dominated by structural work (∼73%) associated to the substrate reconstruction whereas the electronic work is the greatest contribution of the reverse energy barrier (∼67%) in the desorption process. Moreover, REF shows that hydrogen chemisorption is driven by charge transfer processes through four electronic events taking place as H approaches the adsorbent surface: (a) intramolecular charge transfer in the adsorbent surface; (b) surface reconstruction; (c) substrate magnetization and adsorbent carbon atom develops a sp3 hybridization to form the σC-H bond; and (d) spontaneous intermolecular charge transfer to reach the final chemisorbed state

  4. The mechanism of chemisorption of hydrogen atom on graphene: Insights from the reaction force and reaction electronic flux

    Energy Technology Data Exchange (ETDEWEB)

    Cortés-Arriagada, Diego, E-mail: dcortesr@uc.cl; Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Soto, Karla; Toro-Labbé, Alejandro [Nucleus Millennium Chemical Processes and Catalysis, Laboratorio de Química Teórica Computacional (QTC), Departamento de Química-Física, Facultad de Química, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Macul, Santiago (Chile)

    2014-10-07

    At the PBE-D3/cc-pVDZ level of theory, the hydrogen chemisorption on graphene was analyzed using the reaction force and reaction electronic flux (REF) theories in combination with electron population analysis. It was found that chemisorption energy barrier is mainly dominated by structural work (∼73%) associated to the substrate reconstruction whereas the electronic work is the greatest contribution of the reverse energy barrier (∼67%) in the desorption process. Moreover, REF shows that hydrogen chemisorption is driven by charge transfer processes through four electronic events taking place as H approaches the adsorbent surface: (a) intramolecular charge transfer in the adsorbent surface; (b) surface reconstruction; (c) substrate magnetization and adsorbent carbon atom develops a sp{sup 3} hybridization to form the σC-H bond; and (d) spontaneous intermolecular charge transfer to reach the final chemisorbed state.

  5. Radial Matrix Elements of Hydrogen Atom and the Correspondence Principle

    Indian Academy of Sciences (India)

    T. N. Chakrabarty

    2004-03-01

    Radial dipole matrix elements having astrophysical importance have been computed for highly excited states of hydrogen atom. Computation is based on Heisenberg’s form of correspondence principle for Coulomb potential. Particular attention has been paid to the choice of classical analogue (c) of principal quantum number (). The computed radial matrix elements are in good agreement with quantum mechanical results. Further, radial matrix elements for few transitions involving high neighboring states of hydrogen atom are presented.

  6. Muon transfer from hot muonic hydrogen atoms to neon

    International Nuclear Information System (INIS)

    A negative muon beam has been directed on adjacent solid layers of hydrogen and neon. Three targets differing by their deuterium concentration were investigated. Muonic hydrogen atoms can drift to the neon layer where the muon is immediately transferred. The time structure of the muonic neon X-rays follows the exponential law with a disappearance rate corresponding to the one of μ-p atoms in each target. The rates λppμ and λpd can be extracted

  7. Fluctuations of spacetime and hyperfine structure of the hydrogen atom

    Energy Technology Data Exchange (ETDEWEB)

    Goeklue, Ertan [ZARM-Universitaet Bremen (Germany); Rivas, Juan Israel; Camacho, Abel [Universidad Autonoma Metropolitana-Iztapalapa, Mexico (Mexico)

    2012-07-01

    We consider the consequences of the presence of metric fluctuations upon the properties of a hydrogen atom. Particularly, we introduce these metric fluctuations in the corresponding effective Schroedinger equation and deduce the modifications that they entail upon the hyperfine structure related to a hydrogen atom. We will find the change that these effects imply for the ground state energy of the system and obtain a bound for its size comparing our theoretical predictions against the experimental uncertainty reported in the literature.

  8. Topics in atomic hydrogen standard research and applications

    Science.gov (United States)

    Peters, H. E.

    1971-01-01

    Hydrogen maser based frequency and time standards have been in continuous use at NASA tracking stations since February 1970, while laboratory work at Goddard has continued in the further development and improvement of hydrogen masers. Concurrently, experimental work has been in progress with a new frequency standard based upon the hydrogen atom using the molecular beam magnetic resonance method. Much of the hydrogen maser technology is directly applicable to the new hydrogen beam standard, and calculations based upon realistic data indicate that the accuracy potential of the hydrogen atomic beam exceeds that of either the cesium beam tube or the hydrogen maser, possibly by several orders of magnitude. In addition, with successful development, the hydrogen beam standard will have several other performance advantages over other devices, particularly exceptional stability and long continuous operating life. Experimental work with a new laboratory hydrogen beam device has recently resulted in the first resonance transition curves, measurements of relative state populations, beam intensities, etc. The most important aspects of both the hydrogen maser and the hydrogen beam work are covered.

  9. Energetics of a Li Atom adsorbed on B/N doped graphene with monovacancy

    Science.gov (United States)

    Rani, Babita; Jindal, V. K.; Dharamvir, Keya

    2016-08-01

    We use density functional theory (DFT) to study the adsorption properties and diffusion of Li atom across B/N-pyridinic graphene. Regardless of the dopant type, B atoms of B-pyridinic graphene lose electron density. On the other hand, N atoms (p-type dopants) have tendency to gain electron density in N-pyridinic graphene. Higher chemical reactivity and electronic conductivity of B/N-pyridinic graphene are responsible for stronger binding of Li with the substrates as compared to pristine graphene. The binding energy of Li with B/N-pyridinic graphene exceeds the cohesive energy of bulk Li, making it energetically unfavourable for Li to form clusters on these substrates. Li atom gets better adsorbed on N-pyridinic graphene due to an additional p-p hybridization of the orbitals while Li on B-pyridinic prefers the ionic bonding. Also, significant distortion of N-pyridinic graphene upon Li adsorption is a consequence of the change in bonding mechanism between Li atom and the substrate. Our results show that bonding character and hence binding energies between Li and graphene can be tuned with the help of B/N doping of monovacancy defects. Further, the sites for most stable adsorption are different for the two types of doped and defective graphene, leading to greater Li uptake capacity of B-pyridinic graphene near the defect. In addition, B-pyridinic graphene offering lower diffusion barrier, ensures better Li kinetics. Thus, B-pyridinic graphene presents itself as a better anode material for LIBs as compared to N-pyridinic graphene.

  10. Quantitative analysis of desorption and decomposition kinetics of formic acid on Cu(111): The importance of hydrogen bonding between adsorbed species

    Energy Technology Data Exchange (ETDEWEB)

    Shiozawa, Yuichiro; Koitaya, Takanori; Mukai, Kozo; Yoshimoto, Shinya; Yoshinobu, Jun, E-mail: yoshinobu@issp.u-tokyo.ac.jp [The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan)

    2015-12-21

    Quantitative analysis of desorption and decomposition kinetics of formic acid (HCOOH) on Cu(111) was performed by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy, and time-resolved infrared reflection absorption spectroscopy. The activation energy for desorption is estimated to be 53–75 kJ/mol by the threshold TPD method as a function of coverage. Vibrational spectra of the first layer HCOOH at 155.3 K show that adsorbed molecules form a polymeric structure via the hydrogen bonding network. Adsorbed HCOOH molecules are dissociated gradually into monodentate formate species. The activation energy for the dissociation into monodentate formate species is estimated to be 65.0 kJ/mol at a submonolayer coverage (0.26 molecules/surface Cu atom). The hydrogen bonding between adsorbed HCOOH species plays an important role in the stabilization of HCOOH on Cu(111). The monodentate formate species are stabilized at higher coverages, because of the lack of vacant sites for the bidentate formation.

  11. Quantitative analysis of desorption and decomposition kinetics of formic acid on Cu(111): The importance of hydrogen bonding between adsorbed species

    Science.gov (United States)

    Shiozawa, Yuichiro; Koitaya, Takanori; Mukai, Kozo; Yoshimoto, Shinya; Yoshinobu, Jun

    2015-12-01

    Quantitative analysis of desorption and decomposition kinetics of formic acid (HCOOH) on Cu(111) was performed by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy, and time-resolved infrared reflection absorption spectroscopy. The activation energy for desorption is estimated to be 53-75 kJ/mol by the threshold TPD method as a function of coverage. Vibrational spectra of the first layer HCOOH at 155.3 K show that adsorbed molecules form a polymeric structure via the hydrogen bonding network. Adsorbed HCOOH molecules are dissociated gradually into monodentate formate species. The activation energy for the dissociation into monodentate formate species is estimated to be 65.0 kJ/mol at a submonolayer coverage (0.26 molecules/surface Cu atom). The hydrogen bonding between adsorbed HCOOH species plays an important role in the stabilization of HCOOH on Cu(111). The monodentate formate species are stabilized at higher coverages, because of the lack of vacant sites for the bidentate formation.

  12. Strain field of interstitial hydrogen atom in body-centered cubic iron and its effect on hydrogen-dislocation interaction

    OpenAIRE

    Wang, Shuai; Takahashi, Keisuke; Hashimoto, Naoyuki; Isobe, Shigehito; Ohnuki, Somei

    2013-01-01

    Effect of hydrogen in body-centered cubic iron is explored by using the density function theory. Hydrogen atoms increase the concentration of free electrons in the simulation cell and have bonding interaction with Fe atom. Caused by anisotropic strain components of hydrogen atoms in the tetrahedral sites, elastic interaction for hydrogen with screw dislocation has been found. The dependence of hydrogen-screw dislocation interaction on hydrogen concentration is confirmed by repeated stress rel...

  13. Recombination of atomic oxygen and hydrogen on amorphous carbon

    International Nuclear Information System (INIS)

    Deposit buildup and fuel entrapment due to amorphous carbon are relevant issues in fusion devices with carbon based plasma facing components. Neutral atomic species play a significant role – atomic hydrogen facilitates the formation of amorphous carbon while atomic oxygen could be used to remove carbon deposits. The kinetics of either reaction depends on the density of neutral species, which in turn is influenced by recombination on the vessel walls. In this work, we measured the probability of heterogeneous recombination of atomic hydrogen and oxygen on amorphous carbon deposits. The recombination coefficients were determined by observing density profiles of atomic species in a closed side-arm of a plasma vessel with amorphous carbon deposit-lined walls. Density profiles were measured with fiber optics catalytic probes. The source of atomic species was inductively coupled radiofrequency plasma. The measured recombination coefficient values were of the order of 10−3 for both species

  14. Excited states of muonium in atomic hydrogen

    Indian Academy of Sciences (India)

    V S Kulhar

    2006-06-01

    Muonium formation in excited states in muon-hydrogen charge-exchange collision is investigated using a method developed in a previous paper. Differential cross-section results are found to resemble positronium formation cross-section results of positron-hydrogen charge-exchange problem. Forward differential and integrated cross-sections are computed for muon energy of 2 keV and higher. Total muonium formation cross-sections are computed using Jackson and Schiff scaling rules. Muonium formation cross-section results obtained from proton-hydrogen charge-exchange cross-section results, using velocity scaling are compared with the results of the present calculation.

  15. Self-assembly of acetate adsorbates drives atomic rearrangement on the Au(110) surface

    Science.gov (United States)

    Hiebel, Fanny; Shong, Bonggeun; Chen, Wei; Madix, Robert J.; Kaxiras, Efthimios; Friend, Cynthia M.

    2016-10-01

    Weak inter-adsorbate interactions are shown to play a crucial role in determining surface structure, with major implications for its catalytic reactivity. This is exemplified here in the case of acetate bound to Au(110), where the small extra energy of the van der Waals interactions among the surface-bound groups drives massive restructuring of the underlying Au. Acetate is a key intermediate in electro-oxidation of CO2 and a poison in partial oxidation reactions. Metal atom migration originates at surface defects and is likely facilitated by weakened Au-Au interactions due to bonding with the acetate. Even though the acetate is a relatively small molecule, weak intermolecular interaction provides the energy required for molecular self-assembly and reorganization of the metal surface.

  16. Electron ionization and spin polarization control of Fe atom adsorbed graphene irradiated by a femtosecond laser

    International Nuclear Information System (INIS)

    We investigate the structural properties and ionized spin electrons of an Fe–graphene system, in which the time-dependent density functional theory (TDDFT) within the generalized gradient approximation is used. The electron dynamics, including electron ionization and ionized electron spin polarization, is described for Fe atom adsorbed graphene under femtosecond laser irradiation. The theoretical results show that the electron ionization and ionized electron spin polarization are sensitive to the laser parameters, such as the incident angle and the peak intensity. The spin polarization presents the maximum value under certain laser parameters, which may be used as a source of spin-polarized electrons. - Highlights: • The structural properties of Fe–graphene system are investigated. • The electron dynamics of Fe–graphene system under laser irradiation are described. • The Fe–graphene system may be used as a source of spin-polarized electrons

  17. Spin-polarized hydrogen adsorbed on the surface of superfluid {sup 4}He

    Energy Technology Data Exchange (ETDEWEB)

    Marín, J. M.; Boronat, J. [Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Campus Nord B4-B5, E-08034 Barcelona (Spain); Markić, L. Vranješ [Faculty of Science, University of Split, HR-21000 Split (Croatia)

    2013-12-14

    The experimental realization of a thin layer of spin-polarized hydrogen H↓ adsorbed on top of the surface of superfluid {sup 4}He provides one of the best examples of a stable, nearly two-dimensional (2D) quantum Bose gas. We report a theoretical study of this system using quantum Monte Carlo methods in the limit of zero temperature. Using the full Hamiltonian of the system, composed of a superfluid {sup 4}He slab and the adsorbed H↓ layer, we calculate the main properties of its ground state using accurate models for the pair interatomic potentials. Comparing the results for the layer with the ones obtained for a strictly 2D setup, we analyze the departure from the 2D character when the density increases. Only when the coverage is rather small the use of a purely 2D model is justified. The condensate fraction of the layer is significantly larger than in 2D at the same surface density, being as large as 60% at the largest coverage studied.

  18. Characterization of an atomic hydrogen source for charge exchange experiments

    Science.gov (United States)

    Leutenegger, M. A.; Beiersdorfer, P.; Betancourt-Martinez, G. L.; Brown, G. V.; Hell, N.; Kelley, R. L.; Kilbourne, C. A.; Magee, E. W.; Porter, F. S.

    2016-11-01

    We characterized the dissociation fraction of a thermal dissociation atomic hydrogen source by injecting the mixed atomic and molecular output of the source into an electron beam ion trap containing highly charged ions and recording the x-ray spectrum generated by charge exchange using a high-resolution x-ray calorimeter spectrometer. We exploit the fact that the charge exchange state-selective capture cross sections are very different for atomic and molecular hydrogen incident on the same ions, enabling a clear spectroscopic diagnostic of the neutral species.

  19. Correlation of adsorption isotherms of hydrogen isotopes on mordenite adsorbents using reactive vacancy solution theory

    Energy Technology Data Exchange (ETDEWEB)

    Munakata, K.; Nakamura, A. [Faculty of Engineering and Ressource Science, Akita University, Akita-shi, Akita (Japan); Kawamura, Y. [Japan Atomic Energy Agency -JAEA, Tokai, Ibaraki (Japan)

    2015-03-15

    The authors have applied the isotherm equations derived from the reactive vacancy solution theory (RVST) to correlation of experimental and highly non-ideal adsorption isotherms of hydrogen and deuterium on a mordenite adsorbent, and have examined the ability of the isotherm equations to match this correlation. Several isotherm equations such as Langmuir, Freundlich, Toth, Vacancy Solution Theory and so forth were also tested, but they did not work. For the Langmuir-Freundlich equation tests have indicated that its 'ability to correlate' of the adsorption isotherms is not satisfactory. For the multi-site Langmuir-Freundlich (MSLF) equation the correlation of the isotherms appears to be somewhat improved but remains unsatisfactory. The results show that the isotherm equations derived from RVST can better correlate the experimental isotherms.

  20. Precision Spectroscopy of Atomic Hydrogen and the Proton Size Puzzle

    Science.gov (United States)

    Udem, Thomas

    2016-05-01

    Precise determination of transition frequencies of simple atomic systems are required for a number of fundamental applications such as tests of quantum electrodynamics (QED), the determination of fundamental constants and nuclear charge radii. The sharpest transition in atomic hydrogen occurs between the metastable 2S state and the 1S ground state. Its transition frequency has now been measured with almost 15 digits accuracy using an optical frequency comb and a cesium atomic clock as a reference. A recent measurement of the Lamb shift in muonic hydrogen is in significant contradiction to the hydrogen data if QED calculations are assumed to be correct. We hope to contribute to the resolution of this so called `proton size puzzle' by providing additional experimental input from the hydrogen side.

  1. Heat capacity of quantum adsorbates: Hydrogen and helium on evaporated gold films

    Energy Technology Data Exchange (ETDEWEB)

    Birmingham, J.T. [Univ. of California, Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley National Lab., CA (United States). Materials Sciences Div.

    1996-06-01

    The author has constructed an apparatus to make specific heat measurements of quantum gases adsorbed on metallic films at temperatures between 0.3 and 4 K. He has used this apparatus to study quench-condensed hydrogen films between 4 and 923 layers thick with J = 1 concentrations between 0.28 and 0.75 deposited on an evaporated gold surface. He has observed that the orientational ordering of the J = 1 molecules depends on the substrate temperature during deposition of the hydrogen film. He has inferred that the density of the films condensed at the lowest temperatures is 25% higher than in bulk H{sub 2} crystals and have observed that the structure of those films is affected by annealing at 3.4 K. The author has measured the J = 1 to J = 0 conversion rate to be comparable to that of the bulk for thick films; however, he found evidence that the gold surface catalyzes conversion in the first two to four layers. He has also used this apparatus to study films of {sup 4}He less than one layer thick adsorbed on an evaporated gold surface. He shows that the phase diagram of the system is similar to that for {sup 4}He/graphite although not as rich in structure, and the phase boundaries occur at different coverages and temperatures. At coverages below about half a layer and at sufficiently high temperatures, the {sup 4}He behaves like a two-dimensional noninteracting Bose gas. At lower temperatures and higher coverages, liquidlike and solidlike behavior is observed. The Appendix shows measurements of the far-infrared absorptivity of the high-{Tc} superconductor La{sub 1.87}Sr{sub 0.13}CuO{sub 4}.

  2. Electronic Structures of Hydrogen and Oxygen Adsorbed Tungsten (3, 2, 0) and Tungsten (8, 7, 0) Surfaces

    Science.gov (United States)

    Bao, Zhuo; Bostwick, Aaron; Rotenberg, Eli; Kevan, Stephen

    2011-03-01

    The Valence band electronic structues of Hydrogen adsorbed and Oxygen adsorbed Tungsten stepped surfaces, Tungsten (3, 2, 0) and (8, 7, 0) surface are investigated using angular-resolved photoemission techniques and ab-initio electronic structure calculation methods. The band features of surface states at different Hydrogen and Oxygen coverages are experimentally distinguished by using photon-energy scanning method. Quasi-one- dimensional band features are found in the surface states with saturated Oxygen coverages of both stepped surfaces. The effects of adsorbate coverages on dimensionalities of surface electronic states are studied using high-resolution band mapping methods and ab-initio calculation methods. Thanks to Department of Energy for the financial supporting of this project.

  3. Fast automated placement of polar hydrogen atoms in protein-ligand complexes

    OpenAIRE

    Lippert Tobias; Rarey Matthias

    2009-01-01

    Abstract Background Hydrogen bonds play a major role in the stabilization of protein-ligand complexes. The ability of a functional group to form them depends on the position of its hydrogen atoms. An accurate knowledge of the positions of hydrogen atoms in proteins is therefore important to correctly identify hydrogen bonds and their properties. The high mobility of hydrogen atoms introduces several degrees of freedom: Tautomeric states, where a hydrogen atom alters its binding partner, torsi...

  4. Manipulation of adsorbed atoms and creation of new structures on room-temperature surfaces with a scanning tunneling microscope.

    Science.gov (United States)

    Whitman, L J; Stroscio, J A; Dragoset, R A; Celotta, R J

    1991-03-01

    A general method of manipulating adsorbed atoms and molecules on room-temperature surfaces with the use of a scanning tunneling microscope is described. By applying an appropriate voltage pulse between the sample and probe tip, adsorbed atoms can be induced to diffuse into the region beneath the tip. The field-induced diffusion occurs preferentially toward the tip during the voltage pulse because of the local potential energy gradient arising from the interaction of the adsorbate dipole moment with the electric field gradient at the surface. Depending upon the surface and pulse parameters, cesium (Cs) structures from one nanometer to a few tens of nanometers across have been created in this way on the (110) surfaces of gallium arsenide (GaAs) and indium antimonide (InSb), including structures that do not naturally occur.

  5. Atomic force microscopy measurements of topography and friction on dotriacontane films adsorbed on a SiO2 surface

    DEFF Research Database (Denmark)

    Trogisch, S.; Simpson, M.J.; Taub, H.;

    2005-01-01

    We report comprehensive atomic force microscopy (AFM) measurements at room temperature of the nanoscale topography and lateral friction on the surface of thin solid films of an intermediate-length normal alkane, dotriacontane (n-C32H66), adsorbed onto a SiO2 surface. Our topographic and frictional...

  6. Characterizing rate inhibition in H{sub 2}O/H{sub 2} gasification via measurement of adsorbed hydrogen concentration

    Energy Technology Data Exchange (ETDEWEB)

    Lussier, M.G.; Zhang, Z.; Miller, D.J. [Michigan State Univ., East Lansing, MI (United States)

    1996-12-31

    Gasification of coal for fuels production is not currently used on a wide scale because extreme conditions are needed to achieve reasonably fast reaction rates. One reason for these extreme conditions is the inhibition of gasification by hydrogen in the reacting gas phase. For example, gasification rate decreases by an order of magnitude with the addition of only 1 ppm hydrogen to steam, and rate has been shown to decline significantly with conversion in hydrogen and steam/hydrogen mixtures. Hydrogen dissociatively chemisorbed onto carbon is very stable, generally accepted as dissociative in nature, and requires temperatures approaching 1800 K to completely desorb. In this study, chars were gasified and the quantity of hydrogen adsorbed measured.

  7. Atomic hydrogen on Mars - Measurements at solar minimum

    Science.gov (United States)

    Levine, J. S.; Mcdougal, D. S.; Anderson, D. E., Jr.; Barker, E. S.

    1978-01-01

    The Copernicus Orbiting Astronomical Observatory was used to obtain measurements of Mars Lyman-alpha (1215.671-angstrom) emission at the solar minimum, which has resulted in the first information on atomic hydrogen concentrations in the upper atmosphere of Mars at the solar minimum. The Copernicus measurements, coupled with the Viking in situ measurements of the temperature (170 plus or minus 30 K) of the upper atmosphere of Mars, indicate that the atomic hydrogen number density at the exobase of Mars (250 kilometers) is about 60 times greater than that deduced from Mariner 6 and 7 Lyman-alpha measurements obtained during a period of high solar activity. The Copernicus results are consistent with Hunten's hypothesis of the diffusion-limited escape of atomic hydrogen from Mars.

  8. Understanding atomic hydrogen behaviour in pumped divertor plasmas

    International Nuclear Information System (INIS)

    In order to set up a data base and diagnostic capability for understanding atomic hydrogen behaviour in pumped divertor plasmas, an experiment and a feasibility study using a novel laser-induced fluorescence (LIF) technique were performed. For the former, combined measurements of LIF tuned to Hα and emission intensities at Hα/Hβ were carried out on the compact helical system (CHS). The comparison of the measured data and a particle simulation code revealed atomic hydrogen behaviour quantitatively, providing a full estimate of toroidally and poloidally asymmetric distributions of hydrogen atoms. In order to supplement data base around the pumped divertor region, the applicability of an LIF technique which uses two-photon excitation from the ground state examined, based on the real optical constraints of the envisaged JET pumped divertor. It was concluded that ii is feasible and the only remaining problem is not a serious one. (orig.)

  9. Quantization of black holes by analogy with hydrogen atoms

    CERN Document Server

    Liu, Chang; Wu, Yu-Mei; Zhang, Yu-Hao

    2015-01-01

    We suggest a proposal of quantization for black holes that is based on an analogy between a black hole and a hydrogen atom. A self-regular Schwarzschild-AdS black hole is investigated, where the mass density of the extreme black hole is given by the probability density of the ground state of hydrogen atoms and the mass densities of non-extreme black holes are chosen to be the probability densities of excited states with no angular momenta. Consequently, it is logical to accept quantization of mean radii of hydrogen atoms as that of black hole horizons. In this way, quantization of total black hole masses is deduced. Furthermore, the quantum hoop conjecture and the Correspondence Principle are discussed.

  10. Atomic displacements due to interstitial hydrogen in Cu and Pd

    Indian Academy of Sciences (India)

    Hitesh Sharma; S Prakash

    2007-08-01

    The density functional theory (DFT) is used to study the atomic interactions in transition metal-based interstitial alloys. The strain field is calculated in the discrete lattice model using Kanzaki method. The total energy and hence atomic forces between interstitial hydrogen and transition metal hosts are calculated using DFT. The norm-conserving pseudopotentials for H, Cu and Pd are generated self-consistently. The dynamical matrices are evaluated considering interaction up to first nearest neighbors whereas impurity-induced forces are calculated with M32H shell (where M = Cu and Pd). The atomic displacements produced by interstitial hydrogen at the octahedral site in Cu and Pd show displacements of 7.36% and 4.3% of the first nearest neighbors respectively. Both Cu and Pd lattices show lattice expansion due to the presence of hydrogen and the obtained average lattice expansion / = 0.177 for Cu and 0.145 for Pd.

  11. The collision between two hydrogen atoms

    CERN Document Server

    Ray, Hasi

    2013-01-01

    The electron-electron correlation term in two-atomic collision is the most important, most difficult term to obtain the effective interatomic potential. Generally the H and H collision is a four center problem. It is extremely difficult to compute the electron-electron correlation term to include the effect of exchange or antisymmetry between two system electrons exactly. All the two-atomic collision related theoretical data differ from each other due to its difference in approximating the electron-electron correlation term. I invent a trick to evaluate the term exactly. Earlier the positronium (Ps) and H system was easily approximated as a three center problem due to the light mass of Ps. My new code for H-H collision using the ab-initio and exact static-exchange model (SEM) can reproduce exactly the same data of Ps and H system just by using the appropriate atomic parameters. The success of the present trick makes the foundation of a big monument in cold and low energy atomic collision physics. The Feshbach...

  12. ESR and related experiments in spin-polarized atomic hydrogen

    International Nuclear Information System (INIS)

    This thesis deals with some experiments in (gaseous) spin-polarized atomic hydrogen. One uses the expression 'stabilized' atomic hydrogen, meaning that by choosing suitable conditions one can suppress the tendency of atoms to recombine into H2 molecules, such that the lifetime of the atomic state is extended by many orders of magnitude. Research is focused at the study of processes that determine the decay rate of polarized H samples, with the ultimate goal of preparing samples of sufficiently high density and at low enough temperature to observe experimentally the behaviour of the (degenerate) quantum gas. ESR (Electron Spin Resonance) appears to be a very suitable measurement technique to study the properties of polarized H. This work describes the introduction of ESR as detection technique, and the first results of an experiment in polarized H using this technique. (orig.)

  13. Fast metastable hydrogen atoms from H2 molecules: twin atoms

    Directory of Open Access Journals (Sweden)

    Trimèche A.

    2015-01-01

    Full Text Available It is a difficult task to obtain “twin atoms”, i.e. pairs of massive particles such that one can perform experiments in the same fashion that is routinely done with “twin photons”. One possible route to obtain such pairs is by dissociating homonuclear diatomic molecules. We address this possibility by investigating the production of metastable H(2s atoms coming from the dissociation of cold H2 molecules produced in a Campargue nozzle beam crossing an electron beam from a high intensity pulsed electron gun. Dissociation by electron impact was chosen to avoid limitations of target molecular excited states due to selection rules. Detectors placed several centimeters away from the collision center, and aligned with respect to possible common molecular dissociation channel, analyze the neutral fragments as a function of their time-of-flight (TOF through Lyman-α detection. Evidence for the first time observed coincidence of pairs of H(2s atoms obtained this way is presented.

  14. Gravitational Corrections to Energy-Levels of a Hydrogen Atom

    Institute of Scientific and Technical Information of China (English)

    ZHAO Zhen-Hua; LIU Yu-Xiao; LI Xi-Guo

    2007-01-01

    The first-order perturbations of the energy levels of a hydrogen atom in central internal gravitational field are investigated.The internal gravitational field is produced by the mass of the atomic nucleus.The energy shifts are calculated for the relativistic 1S,2S,2P,3S,3P,3D,4S,and 4P levels with Schwarzschild metric.The calculated results show that the gravitational corrections are sensitive to the total angular momentum quantum number.

  15. Multiphoton resonance ionization for hydrogen atom in laser field

    International Nuclear Information System (INIS)

    The Schroedinger equation of hydrogen atom in laser field is expanded by Floquet wave and can be solved by the iterative method. The atomic ionization by laser field is a complex eigenvalue problem, which is formed from differential equation and boundary condition. Then the formula of the multiphoton resonance ionization in a linear polarization laser field was obtained and it is compared with the experiment

  16. On the stability of the hydrogen atom

    International Nuclear Information System (INIS)

    Making reference to the solution of the Schroedinger equation does not give much physical insight into the problem of stability because it is far from obvious how the conclusion follows from the equation. It is pointed out that the common arguments derived from the Heisenberg uncertainty principle are not sufficient to establish the existence of a stable ground state. It is shown how the proof for a lower bound of the hydrogen hamiltonian may be recast into physical terms by introducing an effective localisation potential. (author)

  17. Determination of atomic hydrogen density in non-thermal hydrogen plasmas via emission actinometry

    Energy Technology Data Exchange (ETDEWEB)

    Wang Weiguo [Laboratory of Plasmas Physical Chemistry, PO Box 288, Dalian University of Technology, Dalian 116024 (China); Xu Yong [Laboratory of Plasmas Physical Chemistry, PO Box 288, Dalian University of Technology, Dalian 116024 (China); Geng Zicai [Laboratory of Plasmas Physical Chemistry, PO Box 288, Dalian University of Technology, Dalian 116024 (China); Liu Zhongwei [Laboratory of Plasmas Physical Chemistry, PO Box 288, Dalian University of Technology, Dalian 116024 (China); Zhu Aimin [Laboratory of Plasmas Physical Chemistry, PO Box 288, Dalian University of Technology, Dalian 116024 (China)

    2007-07-21

    Atomic hydrogen plays an important role in the chemical vapour deposition of diamond and other functional materials. This paper reports the experimental determinations of atomic hydrogen density in dielectric barrier discharge hydrogen plasmas via optical emission spectrometry using Ar as an actinometer. At certain discharge conditions (ac 24 kHz, 28 kV of peak-to-peak voltage), the approximate hydrogen dissociation fractions calculated from the emission intensities with respect to electron temperatures obtained with the Langmuir probe, are decreased from 0.099 to 0.01 as the gas pressure increases from 2 to 4 Torr. The relative H atom mole fractions as a function of discharge parameters (spatial position and gas flow rate) have been investigated. It is shown that the discharge characteristics strongly depend on the spatial position but not on the gas flow rate. The influences of the above operating parameters on the emission intensities have been discussed.

  18. Determination of atomic hydrogen density in non-thermal hydrogen plasmas via emission actinometry

    International Nuclear Information System (INIS)

    Atomic hydrogen plays an important role in the chemical vapour deposition of diamond and other functional materials. This paper reports the experimental determinations of atomic hydrogen density in dielectric barrier discharge hydrogen plasmas via optical emission spectrometry using Ar as an actinometer. At certain discharge conditions (ac 24 kHz, 28 kV of peak-to-peak voltage), the approximate hydrogen dissociation fractions calculated from the emission intensities with respect to electron temperatures obtained with the Langmuir probe, are decreased from 0.099 to 0.01 as the gas pressure increases from 2 to 4 Torr. The relative H atom mole fractions as a function of discharge parameters (spatial position and gas flow rate) have been investigated. It is shown that the discharge characteristics strongly depend on the spatial position but not on the gas flow rate. The influences of the above operating parameters on the emission intensities have been discussed

  19. Hydrogen bonding tunes the early stage of hydrogen-atom abstracting reaction.

    Science.gov (United States)

    Yang, Yang; Liu, Lei; Chen, Junsheng; Han, Keli

    2014-09-01

    The spontaneous and collision-assisted hydrogen-atom abstracting reaction (HA) dynamics of triplet benzil are investigated through the combination of transient absorption spectroscopy with TD-DFT calculations. HA dynamics exhibit a remarkable dependence on the hydrogen donor properties. The effects of the triplet-state hydrogen bonding on the reaction dynamics are illustrated. In particular, it is experimentally observed that strengthened triplet-state hydrogen bonding could accelerate the HA, whereas weakened triplet-state hydrogen bonding would postpone the HA. The triplet-state hydrogen bonding has great influences on the early stage of the HA reaction, while the bond dissociation energy of the hydrogen donors determines the subsequent reaction pathways. Protic solvents could sustain longer lifetimes of the excited-state intermediate formed after HA than non-protic solvents by 10 μs. This investigation provides insights into the HA dynamics and guidance to improve the product efficiency of photochemical reactions. PMID:25036436

  20. Variational Perturbation Treatment of the Confined Hydrogen Atom

    Science.gov (United States)

    Montgomery, H. E., Jr.

    2011-01-01

    The Schrodinger equation for the ground state of a hydrogen atom confined at the centre of an impenetrable cavity is treated using variational perturbation theory. Energies calculated from variational perturbation theory are comparable in accuracy to the results from a direct numerical solution. The goal of this exercise is to introduce the…

  1. The Confined Hydrogen Atom with a Moving Nucleus

    Science.gov (United States)

    Fernandez, Francisco M.

    2010-01-01

    We study the hydrogen atom confined to a spherical box with impenetrable walls but, unlike earlier pedagogical articles on the subject, we assume that the nucleus also moves. We obtain the ground-state energy approximately by means of first-order perturbation theory and show that it is greater than that for the case in which the nucleus is clamped…

  2. Quantum-Classical Connection for Hydrogen Atom-Like Systems

    Science.gov (United States)

    Syam, Debapriyo; Roy, Arup

    2011-01-01

    The Bohr-Sommerfeld quantum theory specifies the rules of quantization for circular and elliptical orbits for a one-electron hydrogen atom-like system. This article illustrates how a formula connecting the principal quantum number "n" and the length of the major axis of an elliptical orbit may be arrived at starting from the quantum…

  3. Modelling spectral properties of non-equilibrium atomic hydrogen plasma

    Science.gov (United States)

    D'Ammando, G.; Pietanza, L. D.; Colonna, G.; Longo, S.; Capitelli, M.

    2010-02-01

    A model to predict the emissivity and absorption coefficient of atomic hydrogen plasma is presented in detail. Non-equilibrium plasma is studied through coupling of the model with a collisional-radiative code for the excited states population as well as with the Boltzmann equation for the electron energy distribution function.

  4. Modelling spectral properties of non-equilibrium atomic hydrogen plasma

    International Nuclear Information System (INIS)

    A model to predict the emissivity and absorption coefficient of atomic hydrogen plasma is presented in detail. Non-equilibrium plasma is studied through coupling of the model with a collisional-radiative code for the excited states population as well as with the Boltzmann equation for the electron energy distribution function.

  5. Positron impact ionization of atomic hydrogen at low energies

    Indian Academy of Sciences (India)

    K Chakrabarti

    2001-04-01

    Low energy positron impact ionization of atomic hydrogen is studies theoretically using the hyperspherical partial wave method of Das [1] in constant 12, equal energy sharing geometry. The TDCS reveal considerable differences in physics compared to electron impact ionization under the same geometry.

  6. Concerted hydrogen-atom abstraction in photosynthetic water oxidation.

    Science.gov (United States)

    Westphal, K L; Tommos, C; Cukier, R I; Babcock, G T

    2000-06-01

    Photosystem II evolves oxygen by using water in the unlikely role of a reductant. The absorption of sunlight by chlorophyll produces highly oxidizing equivalents that are filled with electrons stripped from water. This proton-coupled redox chemistry occurs at the oxygen-evolving complex, which contains a tetramanganese cluster, a redox-active tyrosine amino acid hydrogen-bonded to a histidine amino acid, a calcium ion and chloride. Hydrogen-atom abstraction by the tyrosyl radical from water bound to the manganese cluster is now widely held to occur in this process, at least for some of the steps in the catalytic cycle. We discuss kinetic and energetic constraints on the hydrogen-atom abstraction process. PMID:10837268

  7. Atomic hydrogen doping in single-crystal vanadium dioxide

    Science.gov (United States)

    Ji, Heng; Hardy, Will; Wei, Jiang; Lin, Jian; Paik, Hanjong; Schlom, Darrell; Natelson, Douglas

    2014-03-01

    Vanadium dioxide is a strongly correlated material with a bulk metal-to-insulator transition (MIT) near 340 K. Previous experiments in single-crystal nanowires (J. Wei et al., Nature Nano. 7, 357-362 (2012)) have shown that catalytic doping with atomic hydrogen can stabilize the high temperature metallic state. In this experiment, we used a hot filament source to split hydrogen molecules and directly dope atomic hydrogen into VO2 material, including epitaxial films and nanowires, without any catalyst. From observations of the wire samples, we infer the relative diffusion rates of H in the monoclinic and rutile crystal structures. Transport measurements of the doped film samples show no temperature-driven transition, but rather a conducting state down to 2K. We present Hall and magnetoresistance measurements on macroscale and mesoscale devices fabricated from the doped films.

  8. Hydrogen atom mass spectrum in the excited states

    Directory of Open Access Journals (Sweden)

    Arezu Jahanshir

    2013-01-01

    Full Text Available Calculation and analysis of energy spectrum in Coulomb potential of atomic systems, and hadrons in relativistic conditions due to requirements of using higher grades of relativistic corrections have attracted physics theoreticians. The ability to create mono-electron ions of heavy, semi-heavy, strange atoms and/or hadrons atoms in laboratory conditions has boomed the need of more precise and meticulous corrections. One of these factors is to determine electron mass and recoil effect of core in this system. Perturbative and variation theories, regardless of recoil effect, have been calculated in this way so far. The method presented in this paper considers recoil effect intervening and without considering that it researches energy spectrum, mass, and constituent mass in the system. To make more sense of the calculations, hydrogen atomic system has been studied to pave calculation methods for other atoms and systems including quarks, glueball, and pomeron which can be over- generalized using the intended potential.

  9. Collisional excitation of water by hydrogen atoms

    CERN Document Server

    Daniel, F; Dagdigian, P J; Dubernet, M -L; lique, F; forêts, G Pineau des

    2014-01-01

    We present quantum dynamical calculations that describe the rotational excitation of H$_2$O due to collisions with H atoms. We used a recent, high accuracy potential energy surface, and solved the collisional dynamics with the close-coupling formalism, for total energies up to 12 000 cm$^{-1}$. From these calculations, we obtained collisional rate coefficients for the first 45 energy levels of both ortho- and para-H$_2$O and for temperatures in the range T = 5-1500 K. These rate coefficients are subsequently compared to the values previously published for the H$_2$O / He and H$_2$O / H$_2$ collisional systems. It is shown that no simple relation exists between the three systems and that specific calculations are thus mandatory.

  10. Electron-impact ionization of atomic hydrogen

    International Nuclear Information System (INIS)

    Since the invention of quantum mechanics, even the simplest example of collisional breakup in a system of charged particles, e- + H -> H+ + e- + e-, has stood as one of the last unsolved fundamental problems in atomic physics. A complete solution requires calculating the energies and directions for a final state in which three charged particles are moving apart. Advances in the formal description of three-body breakup have yet to lead to a viable computational method. Traditional approaches, based on two-body formalisms, have been unable to produce differential cross sections for the three-body final state. Now, by using a mathematical transformation of the Schrodinger equation that makes the final state tractable, a complete solution has finally been achieved, Under this transformation, the scattering wave function can be calculated without imposing explicit scattering boundary conditions. This approach has produced the first triple differential cross sections that agree on an absolute scale with experiment as well as the first ab initio calculations of the single differential cross section

  11. Studies on the interaction of hydrogen atoms with diamond surface

    International Nuclear Information System (INIS)

    The vibration modes of hydrogen-atom adsorption on the diamond surface were studied with high resolution-electron energy loss spectroscopy. Two main losses were observed at 360 MeV and 160 MeV. They are assigned to the C-H stretch vibrations and the angle-changing deformation vibrations respectively. Replacing H-atom with D-atom, isotopic shifts were observed in the loss spectra. Heating the diamond surface to 900 deg C, all of the loss features disappear, but an inelastic continuous loss-structure was observed. Due to H-atom desorption, the dangling-bonds became horizontal bonds on the diamond surface, resulting in the graphitization of diamond surface. The appearance of the inelastic continuous loss-structure was the characteristic of graphite π-band. The graphitization of the diamond surface was affirmed further by UPS and AES studies

  12. Unparticle contribution to the hydrogen atom ground state energy

    Science.gov (United States)

    Wondrak, Michael F.; Nicolini, Piero; Bleicher, Marcus

    2016-08-01

    In the present work we study the effect of unparticle modified static potentials on the energy levels of the hydrogen atom. By using Rayleigh-Schrödinger perturbation theory, we obtain the energy shift of the ground state and compare it with experimental data. Bounds on the unparticle energy scale ΛU as a function of the scaling dimension dU and the coupling constant λ are derived. We show that there exists a parameter region where bounds on ΛU are stringent, signaling that unparticles could be tested in atomic physics experiments.

  13. Hydrogen negative ions and collisions of atomic particles

    International Nuclear Information System (INIS)

    This paper will be an overview presenting some of the basic atomic collisions processes (gas phase) which are fundamental to production and destruction of H-(D-). More detailed discussions of the most important processes will be left to other papers at this Symposium, and primarily new results since the 1977 Symposium will be discussed. Recent results provide insight into mechanisms responsible for the high H-(D-) ion fractions in hydrogen gas discharges, and the ion-atom collision processes important for double capture negative ion sources are better understood than in 1977

  14. Arbitrary excitation of atomic hydrogen at high energies

    International Nuclear Information System (INIS)

    Because of the growing need of excitation cross-section data of atomic hydrogen by fully stripped heavy ions for the preparation of an atomic database for neutral-beam penetration in large tokamaks, we have calculated these data in the framework of the first-order Born approximation for n≤20 in the energy range of 0.1 to 1.5 MeV/amu. The present computed results are found to be in agreement with the existing observed results. From the present calculation it also appears that the contribution from subshells characterized by l>3 is always less than 2%

  15. Laser stripping of hydrogen atoms by direct ionization

    International Nuclear Information System (INIS)

    Direct ionization of hydrogen atoms by laser irradiation is investigated as a potential new scheme to generate proton beams without stripping foils. The time-dependent Schroedinger equation describing the atom-radiation interaction is numerically solved obtaining accurate ionization cross-sections for a broad range of laser wavelengths, durations and energies. Parameters are identified where the Doppler frequency up-shift of radiation colliding with relativistic particles can lead to efficient ionization over large volumes and broad bandwidths using currently available lasers

  16. Charge exchange between hydrogen atoms and fully stripped heavy ions

    International Nuclear Information System (INIS)

    Charge exchange between multicharged ions and background atomic and molecular gases represents one of the limitations to the attainment of high charge states in heavy ion sources, particularly containment sources. An attempt is made to study systematically a particularly simple but in many respects representative class of such reactions, namely charge transfer between atomic hydrogen and fully stripped heavy ions. Approximate cross sections for these processes in the low keV range of collision energies were obtained using a multistate Landau--Zener method. The energy and Z dependences of the cross sections are discussed

  17. A New Pseudospectral Method for Calculations of Hydrogen Atom in Arbitrary External Fields

    Institute of Scientific and Technical Information of China (English)

    QIAO Hao-Xue; LI Bai-Wen1

    2002-01-01

    A new pseudospectral method was introduced to calculate wavefunctions and energy levels of hydrogen atom in arbitrary potential. Some results of hydrogen atom in uniform magnetic fields were presented, high accuracy of results was obtained with simple calculations, and our calculations show very fast convergence. It suggests a new methodfor calculations of hydrogen atom in external fields.

  18. A discrete variable representation for electron-hydrogen atom scattering

    Energy Technology Data Exchange (ETDEWEB)

    Gaucher, L.F.

    1994-08-01

    A discrete variable representation (DVR) suitable for treating the quantum scattering of a low energy electron from a hydrogen atom is presented. The benefits of DVR techniques (e.g. the removal of the requirement of calculating multidimensional potential energy matrix elements and the availability of iterative sparse matrix diagonalization/inversion algorithms) have for many years been applied successfully to studies of quantum molecular scattering. Unfortunately, the presence of a Coulomb singularity at the electrically unshielded center of a hydrogen atom requires high radial grid point densities in this region of the scattering coordinate, while the presence of finite kinetic energy in the asymptotic scattering electron also requires a sufficiently large radial grid point density at moderate distances from the nucleus. The constraints imposed by these two length scales have made application of current DVR methods to this scattering event difficult.

  19. Electron capture in collisions of S4+ with atomic hydrogen

    International Nuclear Information System (INIS)

    Charge transfer processes due to collisions of ground state S4+(3s21S) ions with atomic hydrogen are investigated for energies between 1 meV u-1 and 10 MeV u-1 using the quantum mechanical molecular-orbital close-coupling (MOCC), atomic-orbital close-coupling, classical trajectory Monte Carlo (CTMC) and continuum distorted wave methods. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond approach. A number of variants of the CTMC approach were explored, including different momentum and radial distributions for the initial state, as well as effective charge and quantum-defect models to determine the corresponding quantum state after capture into final partially stripped S3+ excited classical states. Hydrogen target isotope effects are explored and rate coefficients for temperatures between 100 and 106 K are also presented. (author)

  20. Fluorescence Quenching of Benzaldehyde in Water by Hydrogen Atom Abstraction.

    Science.gov (United States)

    Fletcher, Katharyn; Bunz, Uwe H F; Dreuw, Andreas

    2016-09-01

    We computed the mechanism of fluorescence quenching of benzaldehyde in water through relaxed potential energy surface scans. Time-dependent density functional theory calculations along the protonation coordinate from water to benzaldehyde reveal that photoexcitation to the bright ππ* (S3 ) state is immediately followed by ultrafast decay to the nπ* (S1 ) state. Evolving along this state, benzaldehyde (BA) abstracts a hydrogen atom, resulting in a BAH(.) and OH(.) radical pair. Benzaldehyde does not act as photobase in water, but abstracts a hydrogen atom from a nearby solvent molecule. The system finally decays back to the ground state by non-radiative decay and an electron transfers back to the OH(.) radical. Proton transfer from BAH(+) to OH(-) restores the initial situation, BA in water.

  1. Investigation of the high-order harmonic generation and ionization of model hydrogen atom and real hydrogen atom in intense laser field

    International Nuclear Information System (INIS)

    Solving time-dependent Schroedinger equation numerically, we investigate the high-order harmonic generation and ionization probability of one dimensional, two dimensional and three dimensional hydrogen atom exposed to intense laser field. In the tunneling ionization regime, our results show that the HHG plateau features and cutoff positions of model hydrogen atoms are well agreement with those of real hydrogen atom, and the trend of changing of the ionization probabilities with time is similar, but the values of ionization probabilities for model atoms are different from ones for three dimensional hydrogen atom. We explain the reason for the difference of ionization probabilities between model atoms and real hydrogen atom according to the semiclassical three-step model. (author)

  2. Identification of new, well-populated amino-acid sidechain rotamers involving hydroxyl-hydrogen atoms and sulfhydryl-hydrogen atoms

    OpenAIRE

    Ho, Bosco K.; Agard, David A.

    2008-01-01

    Background An important element in homology modeling is the use of rotamers to parameterize the sidechain conformation. Despite the many libraries of sidechain rotamers that have been developed, a number of rotamers have been overlooked, due to the fact that they involve hydrogen atoms. Results We identify new, well-populated rotamers that involve the hydroxyl-hydrogen atoms of Ser, Thr and Tyr, and the sulfhydryl-hydrogen atom of Cys, using high-resolution crystal structures (

  3. Identification of new, well-populated amino-acid sidechain rotamers involving hydroxyl-hydrogen atoms and sulfhydryl-hydrogen atoms

    OpenAIRE

    Agard David A; Ho Bosco K

    2008-01-01

    Abstract Background An important element in homology modeling is the use of rotamers to parameterize the sidechain conformation. Despite the many libraries of sidechain rotamers that have been developed, a number of rotamers have been overlooked, due to the fact that they involve hydrogen atoms. Results We identify new, well-populated rotamers that involve the hydroxyl-hydrogen atoms of Ser, Thr and Tyr, and the sulfhydryl-hydrogen atom of Cys, using high-resolution crystal structures (

  4. Mesoporous Silica Nanoparticles as an Adsorbent for Preconcentration and Determination of Trace Amount of Nickel in Environmental Samples by Atom Trap Flame Atomic Absorption Spectrometry

    Science.gov (United States)

    Shirkhanloo, H.; Falahnejad, M.; Zavvar Mousavi, H.

    2016-01-01

    A rapid enrichment method based on solid-phase extraction (SPE) has been established for preconcentration and separation of trace Ni(II) ions in water samples prior to their determination by atom trap flame atomic absorption spectrometry. A column filled with bulky NH2-UVM7 was used as the novel adsorbent. Under optimal conditions, the linear range, limit of detection (LOD), and preconcentration factor (PF) were 3-92 μg/L, 0.8 μg/L, and 100, respectively. The validity of the method was checked by the standard reference material.

  5. Variable scaling method and Stark effect in hydrogen atom

    International Nuclear Information System (INIS)

    By relating the Stark effect problem in hydrogen-like atoms to that of the spherical anharmonic oscillator we have found simple formulas for energy eigenvalues for the Stark effect. Matrix elements have been calculated using 0(2,1) algebra technique after Armstrong and then the variable scaling method has been used to find optimal solutions. Our numerical results are compared with those of Hioe and Yoo and also with the results obtained by Lanczos. (author)

  6. Dirac equation in noncommutative space for hydrogen atom

    Energy Technology Data Exchange (ETDEWEB)

    Adorno, T.C., E-mail: tadorno@nonada.if.usp.b [Instituto de Fisica, Universidade de Sao Paulo, Caixa Postal 66318, CEP 05508-090 Sao Paulo, SP (Brazil); Baldiotti, M.C., E-mail: baldiott@fma.if.usp.b [Instituto de Fisica, Universidade de Sao Paulo, Caixa Postal 66318, CEP 05508-090 Sao Paulo, SP (Brazil); Chaichian, M., E-mail: Masud.Chaichian@helsinki.f [Department of Physics, University of Helsinki and Helsinki Institute of Physics, PO Box 64, FIN-00014 Helsinki (Finland); Gitman, D.M., E-mail: gitman@dfn.if.usp.b [Instituto de Fisica, Universidade de Sao Paulo, Caixa Postal 66318, CEP 05508-090 Sao Paulo, SP (Brazil); Tureanu, A., E-mail: Anca.Tureanu@helsinki.f [Department of Physics, University of Helsinki and Helsinki Institute of Physics, PO Box 64, FIN-00014 Helsinki (Finland)

    2009-11-30

    We consider the energy levels of a hydrogen-like atom in the framework of theta-modified, due to space noncommutativity, Dirac equation with Coulomb field. It is shown that on the noncommutative (NC) space the degeneracy of the levels 2S{sub 1/2}, 2P{sub 1/2} and 2P{sub 3/2} is lifted completely, such that new transition channels are allowed.

  7. Dirac Equation in Noncommutative Space for Hydrogen Atom

    CERN Document Server

    Adorno, T C; Chaichian, M; Gitman, D M; Tureanu, A

    2009-01-01

    We consider the energy levels of a hydrogen-like atom in the framework of $\\theta $-modified, due to space noncommutativity, Dirac equation with Coulomb field. It is shown that on the noncommutative (NC) space the degeneracy of the levels $2S_{1/2}, 2P_{1/2}$ and $ 2P_{3/2}$ is lifted completely, such that new transition channels are allowed.

  8. Phase Space Structures Explain Hydrogen Atom Roaming in Formaldehyde Decomposition

    OpenAIRE

    Mauguiere, Frederic A L; Collins, Peter R C; Kramer, Zeb C.; Carpenter, Barry K.; Ezra, Gregory S.; Farantos, Stavros; Wiggins, Stephen R

    2015-01-01

    We re-examine the prototypical roaming reaction—hydrogen atom roaming in formaldehyde decomposition—from a phase space perspective. Specifically, we address the question “why do trajectories roam, rather than dissociate through the radical channel?” We describe and compute the phase space structures that define and control all possible reactive events for this reaction, as well as provide a dynamically exact description of the roaming region in phase space. Using these phase space constructs,...

  9. Relativistic Ionization of Hydrogen Atoms by Positron Impact

    OpenAIRE

    Amal Chahboune; Bouzid Manaut; Elmostafa Hrour; Souad Taj

    2016-01-01

    Relativistic triple differential cross-sections (TDCS) for ionization of hydrogen atoms by positron impact have been calculated in the symmetric coplanar geometry. We have used Dirac wave functions to describe free electron’s and positron’s sates. The relativistic formalism is examined by taking the non relativistic limit. Present results are compared with those for the corresponding electron-impact case. In the first Born approximation, we found that the TDCS for positron impact ionization e...

  10. Interaction of atomic hydrogen with charcoal at 77 K

    International Nuclear Information System (INIS)

    Full text: When the inner surface of the ITER pumping duct is covered with a thin αN-tilde:H film, the hydrogen recombination coefficient can be reduced. In this case, atomic hydrogen can reach the cryopump region and interact with charcoal cryosorbent. The interaction of thermal hydrogen molecules and atoms with charcoal has been analyzed by sorption measurements and TDS at 77 K. A stream quartz reactor with H2 RF discharge was used for the production of H atoms. The ratio of H and H2 in mixture in the afterglow zone was 1/10000. After exposure in H/H2 mixture the tube section with charcoal was warmed up to 300 K. In reference experiments the same sample of charcoal was exposed successively in H2 and CH4. After sample exposure in H/H2 mixture, the TD peak shifted to higher temperatures from 125 K (peak temperature after exposure in H2) to 150 K. The high temperature shoulder of this peak coincided with the temperature of methane release. The wide spectrum of heavy hydrocarbons formed at 77 K was registered by mass-spectrometry at charcoal heating up to 700 K. The specific adsorption volume of charcoal measured by N2 adsorption at 77 K decreased by 10-15%. (author)

  11. Manufacture and deflagration of an atomic hydrogen propellant

    Science.gov (United States)

    Rosen, G.

    1974-01-01

    It is observed that the use of very low temperatures (in the range from 0.1 to 1.5 K) produced by advanced cryogenic apparatus and the use of very strong magnetic fields (in the range from 50 to 100 kG) produced by superconducting magnets can yield a significant improvement in the atomic hydrogen trapping effectiveness of an H2 matrix. The use of a radioactive beta-ray emiter isotope may yield H-H2 propellants (with a specific impulse of about 740 sec) by secondary electron impact dissociations of H2 in an impregnated matrix maintained below 1 K in a strong magnetic field. Another method for manufacturing an H-H2 propellant involves bombardment of supercooled solid H2 with a cyclotron-produced beam of 10-MeV hydrogen atoms. The matrix-isolated atomic hydrogen must be used directly without prior melting as a solid propellant, and an analysis of the steady deflagration is presented.

  12. The atomic hydrogen cloud in the saturnian system

    Science.gov (United States)

    Tseng, W.-L.; Johnson, R. E.; Ip, W.-H.

    2013-09-01

    The importance of Titan's H torus shaped by solar radiation pressure and of hydrogen atoms flowing out of Saturn's atmosphere in forming the broad hydrogen cloud in Saturn's magnetosphere is still debated. Since the Saturnian system also contains a water product torus which originates from the Enceladus plumes, the icy ring particles, and the inner icy satellites, as well as Titan's H2 torus, we have carried out a global investigation of the atomic hydrogen cloud taking into account all sources. We show that the velocity and angle distributions of the hot H ejected from Saturn's atmosphere following electron-impact dissociation of H2 are modified by collisions with the ambient atmospheric H2 and H. This in turn affects the morphology of the escaping hydrogen from Saturn, as does the morphology of the ionospheric electron distribution. Although an exact agreement with the Cassini observations is not obtained, our simulations show that H directly escaping from Titan is the dominant contributor in the outer magnetosphere. Of the total number of H observed by Cassini from 1 to 5RS, ∼5.7×1034, our simulations suggest ∼20% is from dissociation in the Enceladus torus, ∼5-10% is from dissociation of H2 in the atmosphere of the main rings, and ∼50% is from Titan's H torus, implying that ∼20% comes from Saturn atmosphere.

  13. THE DYNAMICS OF HYDROGEN ATOM ABSTRACTION FROM POLYATOMIC MOLECULES.

    Energy Technology Data Exchange (ETDEWEB)

    LIU,X.; SUITS,A.G.

    2002-11-21

    The hydrogen atom abstraction reaction is an important fundamental process that is extensively involved in atmospheric and combustion chemistry. The practical significance of this type of reaction with polyatomic hydrocarbons is manifest, which has led to many kinetics studies. The detailed understanding of these reactions requires corresponding dynamics studies. However, in comparison to the A + HX {radical} AH + X reactions, the study of the dynamics of A + HR {yields} AH + R reactions is much more difficult, both experimentally and theoretically (here and in the following, A stands for an atom, X stands for a halogen atom, and R stands for a polyatomic hydrocarbon radical). The complication stems from the structured R, in contrast to the structureless X. First of all, there are many internal degrees of freedom in R that can participate in the reaction. In addition, there are different carbon sites from which an H atom can be abstracted, and the dynamics are correspondingly different; there are also multiple identical carbon sites in HR and in the picture of a local reaction, there exist competitions between neighboring H atoms, and so on. Despite this complexity, there have been continuing efforts to obtain insight into the dynamics of these reactions. In this chapter, some examples are presented, including the reactions of ground state H, Cl, and O atoms, with particular focus on our recent work using imaging to obtain the differential cross sections for these reactions.

  14. Action of Mercaptan and Disulfide in Hydrogen Atom Exchange Reactions

    International Nuclear Information System (INIS)

    Free- radical, photochemical, and high-energy radiation-induced reactions may be catalysed or inhibited by rapid hydrogen atom exchange reactions of mercaptans and disulfides. The radical-induced, light-initiated, and benzophenone-sensitized decarbonylations of aldehydes are catalysed by mercaptans. The chain-propagating hydrogen transfer reaction, R' + RCH = O -> RH + RC = O , is made more rapid by a similar sequence of hydrogen atom transfers involving the sulfur compound: R' + C6H5CH2SH -> RH + C6H5CH2S'; C6H5CH2S + RCH = 0 -> C6H5CH2SH + RC = 0. The photoreduction of benzophenone in 2-propanol leads to benzpinacol by a non-chain reaction via the radicals (C6H5)2C-OH and (CH3)2COH. The reaction is retarded and inhibited by mercaptan and disulfide, which reconvert the radicals to the starting materials by rapid hydrogen transfer reactions and are themselves regenerated in their alternate valence states, each molecule of sulfur compound negating the chemical consequences of many quanta: (C6H5)2C-OH + AS' -> (C6H5)2C = O + ASH; (CH3)2C-OH + ASH -> (CH3)2C = 0 + AS'. Proof of the mechanism is found in: equilibration of initially present mercaptan or disulfide during inhibition; in racemization of optically active alcohol during inhibition; in deuterium exchange during inhibition. Similar inhibition is seen when only one intermediate radical is formed, as in the benzophenone- benzhydrol and acetophenone-α-methyl-benzyl alcohol systems. Inhibition by sulfur compounds, by the same mechanism, is found in the 60Co γ-ray induced conversion of benzophenone to benzpinacol; naphthalene has no protecting effect on benzophenone in the 60Co system, while quenching the photochemical reaction. The protection by sulfur compounds of solutes against radiation damage thus results from hydrogen atom transfer reactions. The photoreduction of benzophenone in an ether is also inhibited by the sulfur compounds, by hydrogen atom transfer reactions. A mechanism exists in this system

  15. Hydrogen atom density in narrow-gap microwave hydrogen plasma determined by calorimetry

    Science.gov (United States)

    Yamada, Takahiro; Ohmi, Hiromasa; Kakiuchi, Hiroaki; Yasutake, Kiyoshi

    2016-02-01

    The density of hydrogen (H) atoms in the narrow-gap microwave hydrogen plasma generated under high-pressure conditions is expected to be very high because of the high input power density of the order of 104 W/cm3. For measuring the H atom density in such a high-pressure and high-density plasma, power-balance calorimetry is suited since a sufficient signal to noise ratio is expected. In this study, H atom density in the narrow-gap microwave hydrogen plasma has been determined by the power-balance calorimetry. The effective input power to the plasma is balanced with the sum of the powers related to the out-going energy per unit time from the plasma region via heat conduction, outflow of high-energy particles, and radiation. These powers can be estimated by simple temperature measurements using thermocouples and optical emission spectroscopy. From the power-balance data, the dissociation fraction of H2 molecules is determined, and the obtained maximum H atom density is (1.3 ± 0.2) × 1018 cm-3. It is found that the H atom density increases monotonically with increasing the energy invested per one H2 molecule within a constant plasma volume.

  16. Negative hydrogen ion conversion into atoms in a plasma hydrogen target

    International Nuclear Information System (INIS)

    To verufy the feasibility of economic hydrogen plasma target and its efficiency a hydrogen plasma target for the conversion of a beam of negative ions of hydrogen isotopes to atoms has been developed and investigated experimentally. Jet of hydrogen or deuterium plasma of 1.5 m total length and 0.8 m length of a target part had approximately 4 cm in diameter. Plasma of 1013 cm-3 density and 5-6 eV electron temperature was generated at source discharge power of tens of kW at 1.5 ms pulse duration. H- ion beam of 0.3 ms pulse duration and 500 keV energy at the Van de Graaf accelerator outlet was analyzed by a magnet and collimated with a diaphragm having 0.5-1 cm aperture installed along one axis with the plasma target solenoid. After passing the target the beam was separated in a magnetic field of a bend solenoid part into three beams: H-, H0 and H+. Each beam was passed a lavsan stripping film of 3500 A thickness and in the form of a proton beam was received by the Faradey cylinder. An experimental value of atom yield is equal to 84.5+-0.5% at 500 keV H- ion energy and for a target thickness nsub(e)L=2x1015 cm-2. It is established that the plasma jet not only well screens itself from an external flow of nonionized gas but also pumps out it ionizing and carrying out to a receiving volume. A sufficiently high value of the conversion ratio of high-energy negative hydrogen ions to atoms as well as high screening and pumping out properties of the hydrogen plasma target permits to hope for its successful application in injectors of high-energy atoms

  17. The role of atomic hydrogen and hydrogen-induced martensites in hydrogen embrittlement of type 304L stainless steel

    Institute of Scientific and Technical Information of China (English)

    潘川; 褚武扬; 李正邦; 梁东图; 宿彦京; 乔利杰

    2002-01-01

    The role of atomic hydrogen and hydrogen-induced martensites in hydrogen embrittlement in slow strain rate tensile tests and hydrogen-induced delayed cracking (HIC) in sustained load tests for type 304 L stainless steel was quantitatively studied.The results indicated that hydrogen-induced martensites formed when hydrogen concentration C0 exceeded 30 ppm,and increased with an increase in C0,i.e.M(vol%)=62-82.5exp(-C0/102).The relative plasticity loss caused by the martensites increased linearly with increasing amount of the martensites,i.e.Iδ(M),%=0.45M(vol %)=27.9-37.1 exp(-C0/102).The plasticity loss caused by atomic hydrogen Iδ(H) increased with an increase in C0 and reached a saturation value Iδ(H)max=40% when C0>100 ppm.Iδ(H) decreased with an increase in strain rate ,i.e.Iδ(H),%=-21.9-9.9,and was zero when ≥c=0.032/s.HIC under sustained load was due to atomic hydrogen,and the threshold stress intensity for HIC decreased linearly with lnC0,i.e.KIH(Mpam1/2)=91.7-10.1 lnC0(ppm).The fracture surface of HIC was dimple if KI was high or/and C0 was low,otherwise it was quasi-cleavage.The boundary line between ductile and brittle fracture surface was KI-54+25exp(-C0/153)=0.``

  18. Changes in the morphology of interstellar ice analogues after hydrogen atom exposure

    CERN Document Server

    Accolla, Mario; Dulieu, François; Manicò, Giulio; Chaabouni, Henda; Matar, Elie; Mokrane, Hakima; Lemaire, Jean Louis; Pirronello, Valerio

    2010-01-01

    The morphology of water ice in the interstellar medium is still an open question. Although accretion of gaseous water could not be the only possible origin of the observed icy mantles covering dust grains in cold molecular clouds, it is well known that water accreted from the gas phase on surfaces kept at 10 K forms ice films that exhibit a very high porosity. It is also known that in the dark clouds H2 formation occurs on the icy surface of dust grains and that part of the energy (4.48 eV) released when adsorbed atoms react to form H2 is deposited in the ice. The experimental study described in the present work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. Using the temperature-programmed desorption (TPD) technique and a method of inversion analysis of TPD spectra, we show that there is an exponential decrease in the porosity of the amorphous water ice sample following D-atom irradiation. This decrease is inversely proportional to the...

  19. Absorption spectrum of very low pressure atomic hydrogen

    CERN Document Server

    Moret-Bailly, Jacques

    2015-01-01

    Spectra of quasars result primarily from interactions of natural light with atomic hydrogen. A visible absorption of a sharp and saturated spectral line in a gas requires a low pressure, so a long path without blushing as a cosmological redshift. Burbidge and Karlsson observed that redshifts of quasars result from fundamental redshifts, written 3K and 4K, that cause a shift of absorbed beta and gamma lines of H to alpha gas line. Thus absorbed spectrum is shifted until an absorbed line overlaps with Lyman alpha line of gas: redshift only occurs if an alpha absorption pumps atoms to 2P state. Thus, space is divided into spherical shells centered on the quasar, containing or not 2P atoms. Neglecting collisional de-excitations in absorbing shells, more and more atoms are excited until amplification of a beam having a long path in a shell, thus perpendicular to the observed ray, is large enough for a superradiant flash at alpha frequency. Energy is provided by atoms and observed ray, absorbing a line at local Lym...

  20. Allowed and forbidden transitions in artificial hydrogen and helium atoms.

    Science.gov (United States)

    Fujisawa, Toshimasa; Austing, David Guy; Tokura, Yasuhiro; Hirayama, Yoshiro; Tarucha, Seigo

    2002-09-19

    The strength of radiative transitions in atoms is governed by selection rules that depend on the occupation of atomic orbitals with electrons. Experiments have shown similar electron occupation of the quantized energy levels in semiconductor quantum dots--often described as artificial atoms. But unlike real atoms, the confinement potential of quantum dots is anisotropic, and the electrons can easily couple with phonons of the material. Here we report electrical pump-and-probe experiments that probe the allowed and 'forbidden' transitions between energy levels under phonon emission in quantum dots with one or two electrons (artificial hydrogen and helium atoms). The forbidden transitions are in fact allowed by higher-order processes where electrons flip their spin. We find that the relaxation time is about 200 micro s for forbidden transitions, 4 to 5 orders of magnitude longer than for allowed transitions. This indicates that the spin degree of freedom is well separated from the orbital degree of freedom, and that the total spin in the quantum dots is an excellent quantum number. This is an encouraging result for potential applications of quantum dots as basic entities for spin-based quantum information storage.

  1. Heat capacity measurements of atoms and molecules adsorbed on evaporated metal films

    Energy Technology Data Exchange (ETDEWEB)

    Kenny, T.W.

    1989-05-01

    Investigations of the properties of absorbed monolayers have received great experimental and theoretical attention recently, both because of the importance of surface processes in practical applications such as catalysis, and the importance of such systems to the understanding of the fundamentals of thermodynamics in two dimensions. We have adapted the composite bolometer technology to the construction of microcalorimeters. For these calorimeters, the adsorption substrate is an evaporated film deposited on one surface of an optically polished sapphire wafer. This approach has allowed us to make the first measurements of the heat capacity of submonolayer films of /sup 4/He adsorbed on metallic films. In contrast to measurements of /sup 4/He adsorbed on all other insulating substrates, we have shown that /sup 4/He on silver films occupies a two-dimensional gas phase over a broad range of coverages and temperatures. Our apparatus has been used to study the heat capacity of Indium flakes. CO multilayers, /sup 4/He adsorbed on sapphire and on Ag films and H/sub 2/ adsorbed on Ag films. The results are compared with appropriate theories. 68 refs., 19 figs.

  2. Heat capacity measurements of atoms and molecules adsorbed on evaporated metal films

    International Nuclear Information System (INIS)

    Investigations of the properties of absorbed monolayers have received great experimental and theoretical attention recently, both because of the importance of surface processes in practical applications such as catalysis, and the importance of such systems to the understanding of the fundamentals of thermodynamics in two dimensions. We have adapted the composite bolometer technology to the construction of microcalorimeters. For these calorimeters, the adsorption substrate is an evaporated film deposited on one surface of an optically polished sapphire wafer. This approach has allowed us to make the first measurements of the heat capacity of submonolayer films of 4He adsorbed on metallic films. In contrast to measurements of 4He adsorbed on all other insulating substrates, we have shown that 4He on silver films occupies a two-dimensional gas phase over a broad range of coverages and temperatures. Our apparatus has been used to study the heat capacity of Indium flakes. CO multilayers, 4He adsorbed on sapphire and on Ag films and H2 adsorbed on Ag films. The results are compared with appropriate theories. 68 refs., 19 figs

  3. The EAGLE simulations: atomic hydrogen associated with galaxies

    CERN Document Server

    Crain, Robert A; Lagos, Claudia del P; Rahmati, Alireza; Schaye, Joop; McCarthy, Ian G; Marasco, Antonino; Bower, Richard G; Schaller, Matthieu; Theuns, Tom; van der Hulst, Thijs

    2016-01-01

    We examine the properties of atomic hydrogen (HI) associated with galaxies in the EAGLE simulations of galaxy formation. EAGLE's feedback parameters were calibrated to reproduce the stellar mass function and galaxy sizes at $z=0.1$, and we assess whether this calibration also yields realistic HI properties. We estimate the self-shielding density with a fitting function calibrated using radiation transport simulations, and correct for molecular hydrogen with empirical or theoretical relations. The `standard-resolution' simulations systematically underestimate HI column densities, leading to an HI deficiency in low-mass ($M_\\star < 10^{10}M_\\odot$) galaxies and poor reproduction of the observed HI mass function. These shortcomings are largely absent from EAGLE simulations featuring a factor of 8 (2) better mass (spatial) resolution, within which the HI mass of galaxies evolves more mildly from $z=1$ to $0$ than in the standard-resolution simulations. The largest-volume simulation reproduces the observed clus...

  4. Asymptotics of Rydberg states for the hydrogen atom

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, L.E. [Virginia Univ., Charlottesville, VA (United States). Dept. of Mathematics; Villegas-Blas, C. [Universidad Nacional Autonoma de Mexico, Instituto de Matematicas, Unidad Cuernavaca, A. P. 273-3 Admon. 3, Cuernavaca Morelos 62251 (Mexico)

    1997-08-01

    The asymptotics of Rydberg states, i.e., highly excited bound states of the hydrogen atom Hamiltonian, and various expectations involving these states are investigated. We show that suitable linear combinations of these states, appropriately rescaled and regarded as functions either in momentum space or configuration space, are highly concentrated on classical momentum space or configuration space Kepler orbits respectively, for large quantum numbers. Expectations of momentum space or configuration space functions with respect to these states are related to time-averages of these functions over Kepler orbits. (orig.)

  5. Absorption spectrum of very low pressure atomic hydrogen

    OpenAIRE

    Moret-Bailly, Jacques

    2015-01-01

    Spectra of quasars result primarily from interactions of natural light with atomic hydrogen. A visible absorption of a sharp and saturated spectral line in a gas requires a low pressure, so a long path without blushing as a cosmological redshift. Burbidge and Karlsson observed that redshifts of quasars result from fundamental redshifts, written 3K and 4K, that cause a shift of absorbed beta and gamma lines of H to alpha gas line. Thus absorbed spectrum is shifted until an absorbed line overla...

  6. Comments on the Hydrogen Atom Spectrum in the Noncommutative Space

    CERN Document Server

    Chaichian, Masud; Tureanu, A

    2002-01-01

    There has been disagreement in the literature on whether the hydrogen atom spectrum receives any tree-level correction due to noncommutativity. Here we shall clarify the issue and show that indeed a general argument on the structure of proton as a nonelementary particle leads to the appearance of such corrections. As a showcase, we evaluate the corrections in a simple nonrelativistic quark model with a result in agreement with the previous one we had obtained by considering the electron moving in the external electric field of proton. Thus the previously obtained bound on the noncommutativity parameter, $\\theta < (10^4 GeV)^{-2}$, using the Lamb shift data, remains valid.

  7. Relativistic Ionization of Hydrogen Atoms by Positron Impact

    Directory of Open Access Journals (Sweden)

    Amal Chahboune

    2016-03-01

    Full Text Available Relativistic triple differential cross-sections (TDCS for ionization of hydrogen atoms by positron impact have been calculated in the symmetric coplanar geometry. We have used Dirac wave functions to describe free electron’s and positron’s sates. The relativistic formalism is examined by taking the non relativistic limit. Present results are compared with those for the corresponding electron-impact case. In the first Born approximation, we found that the TDCS for positron impact ionization exceeds that for electron impact for all energies in accordance with the result obtained by several other theories.

  8. Wave mechanics in quantum phase space: hydrogen atom

    Institute of Scientific and Technical Information of China (English)

    LU Jun

    2007-01-01

    The rigorous sohutions of the stationary Schr(o)dinger equation for hydrogen atom are solved with the wave-mechanics method within the framework of the quantum phase-space representation established by Torres-Vega and Frederick. The "Fourier-like"projection transformations of wave function from the phase space to position and momentum spaces are extended to three-dimensional systems. The eigenfunctions in general position and momentum spaces could be obtained through the transformations from eigenfunction in the phase space.

  9. Stiff Stability of the Hydrogen atom in dissipative Fokker electrodynamics

    CERN Document Server

    De Luca, J

    2005-01-01

    We introduce an ad-hoc electrodynamics with advanced and retarded Lienard-Wiechert interactions plus the dissipative Lorentz-Dirac self-interaction force. We study the covariant dynamical system of the electromagnetic two-body problem, i.e., the hydrogen atom. We perform the linear stability analysis of circular orbits for oscillations perpendicular to the orbital plane. In particular we study the normal modes of the linearized dynamics that have an arbitrarily large imaginary eigenvalue. These large eigenvalues are fast frequencies that introduce a fast (stiff) timescale into the dynamics. As an application, we study the phenomenon of resonant dissipation, i.e., a motion where both particles recoil together in a drifting circular orbit (a bound state), while the atom dissipates center-of-mass energy only. This balancing of the stiff dynamics is established by the existence of a quartic resonant constant that locks the dynamics to the neighborhood of the recoiling circular orbit. The resonance condition quant...

  10. The photon scattering cross-sections of atomic hydrogen

    CERN Document Server

    Grunefeld, Swaantje J; Cheng, Yongjun

    2016-01-01

    We present a unified view of the frequency dependence of the various scattering processes involved when a neutral hydrogen atom interacts with a monochromatic, linearly-polarized photon. A computational approach is employed of the atom trapped by a finite-sized-box due to a finite basis-set expansion, which generates a set of transition matrix elements between $E0$ pseudostates. We introduce a general computational methodology that enables the computation of the frequency-dependent dipole transition polarizability with one real and two different imaginary contributions. These dipole transition polarizabilities are related to the cross-sections of one-photon photoionization, Rayleigh, Raman, and Compton scattering. Our numerical calculations reveal individual Raman scattering cross-sections above threshold that can rapidly vanish and revive. Furthermore, our numerical Compton cross-sections do not overtly suffer from the infra-red divergence problem, and are three orders-of-magnitude higher than previous analy...

  11. Endohedrally confined hydrogen atom with a moving nucleus

    CERN Document Server

    Randazzo, Juan M

    2016-01-01

    We studied the hydrogen atom as a system of two quantum particles in different confinement conditions; a spherical-impenetrable-wall cavity and a fullerene molecule cage. The motion is referred to the center of spherical cavities, and the Schr\\"{o}dinger equation solved by means of a Generalized Sturmian Function expansion in spherical coordinates. The solutions present different properties from the ones described by the many models in the literature, where the proton is fixed in space and only the electron is considered as a quantum particle. Our results show that the position of the proton (i.e. the center of mas of the H atom) is very sensitive to the confinement condition, and could vary substantially from one state to another, from being sharply centered to being localized outside the fullerene molecule. Interchange of the localization characteristics between the states when varying the strength of the fullerene cage and mass occurred through crossing phenomena.

  12. Ionization of hydrogen atoms by circularly polarized microwaves

    Energy Technology Data Exchange (ETDEWEB)

    Gebarowski, R.; Zakrzewski, J. (Instytut Fizyki Uniwersytetu Jagiellonskiego, ulica Reymonta 4, 30-059 Krakow (Poland) Laboratoire Kastler-Brossel, Universite Pierre et Marie Curie, T12, E1, 4 place Jussieu, 75272 Paris Cedex 05 (France))

    1995-02-01

    Ionization of hydrogen Rydberg atoms by [ital circularly] polarized microwaves is studied numerically within the framework of classical mechanics. Both the simplified two-dimensional model (in which the plane of polarization coincides with the orbit plane) and a fully three-dimensional system are considered. It is shown that the ionization proceeds in the diffusive manner for all microwave frequencies except the low-frequency limit. The threshold for diffusive excitation as well as the diffusion speed is strongly dependent on the initial state of the system for smooth pulse excitation. In a high-frequency limit the ionization threshold rises sharply---the atom is much more resistant to the excitation. Two distinct regimes of stabilization windows (regions where the ionization decreases with increasing field amplitude), one in the strong short-laser-pulse domain and the other in the weak microwave domain, are identified and discussed.

  13. Ionization of atomic hydrogen by 30 1000 keV antiprotons

    Energy Technology Data Exchange (ETDEWEB)

    Knudsen, H.; Mikkelsen, U.; Paludan, K. [Institute of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); Kirsebom, K.; Moller, S.P.; Uggerhoj, E. [Institute for Synchrotron Radiation, University of Aarhus, DK-8000 Aarhus C (Denmark); Slevin, J. [Department of Experimental Physics, St. Patrick`s College, Maynooth (Ireland); Charlton, M. [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom); Morenzoni, E. [Paul Scherrer Institut, Villigen, CH-4234 (Switzerland)

    1995-06-05

    Ionization in collisions between antiprotons and atomic hydrogen is perhaps the least complicated and most fundamental process that can be treated by atomic-collision theory. We present measurements of the ionization cross section for 30--1000 keV antiprotons colliding with atomic hydrogen.

  14. Scanning electrochemical microscopy: surface interrogation of adsorbed hydrogen and the open circuit catalytic decomposition of formic acid at platinum.

    Science.gov (United States)

    Rodríguez-López, Joaquín; Bard, Allen J

    2010-04-14

    The surface interrogation mode of scanning electrochemical microscopy (SECM) is extended to the in situ quantification of adsorbed hydrogen, H(ads), at polycrystalline platinum. The methodology consists of the production, at an interrogator electrode, of an oxidized species that is able to react with H(ads) on the Pt surface and report the amounts of this adsorbate through the SECM feedback response. The technique is validated by comparison to the electrochemical underpotential deposition (UPD) of hydrogen on Pt. We include an evaluation of electrochemical mediators for their use as oxidizing reporters for adsorbed species at platinum; a notable finding is the ability of tetramethyl-p-phenylenediamine (TMPD) to oxidize (interrogate) H(ads) on Pt at low pH (0.5 M H(2)SO(4) or 1 M HClO(4)) and with minimal background effects. As a case study, the decomposition of formic acid (HCOOH) in acidic media at open circuit on Pt was investigated. Our results suggest that formic acid decomposes at the surface of unbiased Pt through a dehydrogenation route to yield H(ads) at the Pt surface. The amount of H(ads) depended on the open circuit potential (OCP) of the Pt electrode at the time of interrogation; at a fixed concentration of HCOOH, a more negative OCP yielded larger amounts of H(ads) until reaching a coulomb limiting coverage close to 1 UPD monolayer of H(ads). The introduction of oxygen into the cell shifted the OCP to more positive potentials and reduced the quantified H(ads); furthermore, the system was shown to be chemically reversible, as several interrogations could be run consecutively and reproducibly regardless of the path taken to reach a given OCP. PMID:20225806

  15. Dynamics of hydrogen-like atom bounded by maximal acceleration

    CERN Document Server

    Friedman, Yaakov

    2012-01-01

    The existence of a maximal acceleration for massive objects was conjectured by Caianiello 30 years ago based on the Heisenberg uncertainty relations. Many consequences of this hypothesis have been studied, but until now, there has been no evidence that boundedness of the acceleration may lead to quantum behavior. In previous research, we predicted the existence of a universal maximal acceleration and developed a new dynamics for which all admissible solutions have an acceleration bounded by the maximal one. Based on W. K\\"{u}ndig's experiment, as reanalyzed by Kholmetskii et al, we estimated its value to be of the order $10^{19}m/s^2$. We present here a solution of our dynamical equation for a classical hydrogen-like atom and show that this dynamics leads to some aspects of quantum behavior. We show that the position of an electron in a hydrogen-like atom can be described only probabilistically. We also show that in this model, the notion of "center of mass" must be modified. This modification supports the no...

  16. Atomic scattering from an adsorbed monolayer solid with a helium beam that penetrates to the substrate

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Bruch, L.W.; Dammann, Bernd

    2013-01-01

    Diffraction and one-phonon inelastic scattering of a thermal energy helium atomic beam are evaluated in the situation that the target monolayer lattice is so dilated that the atomic beam penetrates to the interlayer region between the monolayer and the substrate. The scattering is simulated...

  17. Atomic scattering from an adsorbed monolayer solid with a helium beam that penetrates to the substrate

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Bruch, L.W.; Dammann, Bernd

    2013-01-01

    Diffraction and one-phonon inelastic scattering of a thermal energy helium atomic beam are evaluated in the situation that the target monolayer lattice is so dilated that the atomic beam penetrates to the interlayer region between the monolayer and the substrate. The scattering is simulated by...

  18. Evaluation of Hydrogen Isotope Exchange Methodology on Adsorbents for Tritium Removal

    International Nuclear Information System (INIS)

    The Savannah River National Laboratory has demonstrated a potential process that can be used to remove tritium from tritiated water using Pt-catalyzed molecular sieves. The process is an elemental isotope exchange process in which H2 (when flowed through the molecular sieves) will exchange with the adsorbed water, D2O, leaving H2O adsorbed on the molecular sieves. Various formulations of catalyzed molecular sieve material were prepared using two different techniques, Pt-implantation and Pt-ion exchange. This technology has been demonstrated for a protium (H) and deuterium (D) system, but can also be used for the removal of tritium from contaminated water (T2O, HTO, and DTO) using D2 (or H2)

  19. Evaluation of hydrogen isotope exchange methodology on adsorbents for tritium removal

    International Nuclear Information System (INIS)

    The Savannah River National Laboratory has demonstrated a potential process that can be used to remove tritium from tritiated water using Pt-catalyzed molecular sieves. The process is an elemental isotope exchange process in which H2 (when flowed through the molecular sieves) will exchange with the adsorbed water, D2O, leaving H2O adsorbed on the molecular sieves. Various formulations of catalyzed molecular sieve material were prepared using two different techniques, Pt-implantation and Pt-ion exchange. This technology has been demonstrated for a protium (H) and deuterium (D) system, but can also be used for the removal of tritium from contaminated water (T2O, HTO, and DTO) using D2 (or H2). (authors)

  20. Structural, electronic, and magnetic properties of transition-metal atom adsorbed two-dimensional GaAs nanosheet

    Science.gov (United States)

    Luo, Jia; Xiang, Gang; Yu, Tian; Lan, Mu; Zhang, Xi

    2016-09-01

    By using first-principles calculations within the framework of density functional theory, the electronic and magnetic properties of 3d transitional metal (TM) atoms (from Sc to Zn) adsorbed monolayer GaAs nanosheets (GaAsNSs) are systematically investigated. Upon TM atom adsorption, GaAsNS, which is a nonmagnetic semiconductor, can be tuned into a magnetic semiconductor (Sc, V, and Fe adsorption), a half-metal (Mn adsorption), or a metal (Co and Cu adsorption). Our calculations show that the strong p-d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the GaAsNSs with Sc, V, and Fe adsorption. However, the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit, resulting in a stronger exchange interaction. Our results may be useful for electronic and magnetic applications of GaAsNS-based materials. Project supported by the National Natural Science Foundation of China (Grant No. 11174212).

  1. Y(sl(2)) Algebra Application in Extended Hydrogen Atom and Monopole Models

    Institute of Scientific and Technical Information of China (English)

    TIAN Li-Jun; ZHANG Hong-Biao; JIN Shuo; XUE Kang

    2004-01-01

    We present the extended hydrogen atom and monopole-hydrogen atom theory through generalizing the usual hydrogen atom model and with a monopole model respectively, in which Y (sl(2) ) algebras are realized. We derive the Hamiltonians of the two models based on the Y(sl(2) ) and the generalized Pauli equation. The energy spectra of the systems are also given in terms of Yangian algebra and quantum mechanics.

  2. Fate of accidental symmetries of the relativistic hydrogen atom in a spherical cavity

    OpenAIRE

    Al-Hashimi, M. H.; Shalaby, A. M.; Wiese, U. -J.

    2015-01-01

    The non-relativistic hydrogen atom enjoys an accidental $SO(4)$ symmetry, that enlarges the rotational $SO(3)$ symmetry, by extending the angular momentum algebra with the Runge-Lenz vector. In the relativistic hydrogen atom the accidental symmetry is partially lifted. Due to the Johnson-Lippmann operator, which commutes with the Dirac Hamiltonian, some degeneracy remains. When the non-relativistic hydrogen atom is put in a spherical cavity of radius $R$ with perfectly reflecting Robin bounda...

  3. The role of vdW interactions in coverage dependent adsorption energies of atomic adsorbates on Pt(111) and Pd(111)

    Science.gov (United States)

    Thirumalai, Hari; Kitchin, John R.

    2016-08-01

    Adsorption, a fundamental process in heterogeneous catalysis is known to be dependent on the adsorbate-adsorbate and surface-adsorbate bonds. van der Waals (vdW) interactions are one of the types of interactions that have not been examined thoroughly as a function of adsorbate coverage. In this work we quantify the vdW interactions for atomic adsorbates on late transition metal surfaces, and determine how these long range forces affect the coverage dependent adsorption energies. We calculate the adsorption energies of carbon, nitrogen, oxygen, sulfur, fluorine, bromine and chlorine species on Pt(111) and Pd(111) at coverages ranging from 1/4 to 1 ML using the BEEF-vdW functional. We observe that adsorption energies remain coverage dependent, and this coverage dependence is shown to be statistically significant. vdW interactions are found to be coverage dependent, but more significantly, they are found to be dependent on molecular properties such as adsorbate size, and consequently, correlate with the adsorbate effective nuclear charge. We observe that these interactions account for a reduction in the binding energy of the system, due to the destabilizing attractive interactions between the adsorbates which weaken its bond with the surface.

  4. X-ray emission spectroscopy applied to glycine adsorbed on Cu(110): An atom and symmetry projected view

    Energy Technology Data Exchange (ETDEWEB)

    Hasselstroem, J.; Karis, O.; Weinelt, M. [Uppsala Univ. (Sweden)] [and others

    1997-04-01

    When a molecule is adsorbed on a metal surface by chemical bonding new electronic states are formed. For noble and transition metals these adsorption-induced states overlap with the much more intense metal d-valence band, making them difficult to probe by for instance direct photoemission. However, it has recently been shown that X-ray emission spectroscopy (XES) can be applied to adsorbate systems. Since the intermediate state involves a core hole, this technique has the power to project out the partial density of states around each atomic site. Both the excitation and deexcitation processes are in general governed by the dipole selection rules. For oriented system, it is hence possible to obtain a complete separation into 2p{sub x}, 2p{sub y} and 2p{sub z} contributions using angular resolved measurements. The authors have applied XES together with other core level spectroscopies to glycine adsorption on Cu(110). Glycine (NH{sub 2}CH{sub 2}COOH) is the smallest amino acid and very suitable to study by core level spectroscopy since it has several functional groups, all well separated in energy by chemical shifts. Its properties are futhermore of biological interest. In summary, the authors have shown that it is possible to apply XES to more complicated molecular adsorbates. The assignment of different electronic states is however not as straight forward as for simple diatomic molecules. For a complete understanding of the redistribution and formation of new electronic states associated with the surface chemical bond, experimental data must be compared to theoretical calculations.

  5. Two-photon photoemission investigation of electronic and dynamical properties of alkali atoms adsorbed on noble metal surfaces

    Science.gov (United States)

    Sametoglu, Vahit

    We present a systematic time-resolved two-photon photoemission study of the electronic and dynamical properties of Li through Cs adsorbed on Cu(111) and Ag(111) surfaces. A fundamental problem in surface science is how to describe the electronic structure of a chemisorption interface based on the intrinsic properties of the interacting materials. Because of their simple s-electron structure, elements of the alkali atom group comprise paradigmatic adsorbates in many theories of chemisorption, whereas the complementary experimental studies are sparse and incomplete. Through a combination of spectroscopic and femtosecond time-resolved surface measurements, we are able to probe systematically the binding energies, symmetries, and electron and nuclear relaxation dynamics of the initially unoccupied alkali atom resonances. As a prelude, we study the two-photon photoemission process occurring at the bare Ag(111) surface. We develop a quantitative model for two-photon photoemission process, where the nonresonant and k-dependent two-photon absorption between the lower and upper sp-bands is modeled by the optical Bloch equations, and the angle-dependent intensities are described by the Fresnel equations. Our two-photon photoemission spectra of Li through Cs chemisorbed Cu(111) and Ag(111) surfaces reveal two resonances with the m = 0 and m = +/-1 symmetry ('m' is the projection of the orbital angular momentum 'l' onto the surface plane). For the m = 0 resonance, which is derived from the hybridization of the ns and npz orbitals of alkali atoms, we find a binding energy of 1.84--1.99 eV below the vacuum level, which is independent of the alkali atom period, and tunes with coverage in a universal manner. At 0.3--0.7 eV higher energy, we discover and identify the m = +/-1 resonance by its characteristic angular intensity distribution, which derives from the antisymmetry of the npx and npy orbitals. We implement a quantitative model for the alkali atom chemisorption based on the

  6. Resonance structure in elastic scattering of electrons from atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Warner, C.D.; King, G.C.; Hammond, P.; Slevin, J.

    1986-10-28

    High-energy-resolution spectra of electrons scattered elastically from atomic hydrogen have been obtained for incident electron energies of 9.2-10.4 eV and at angles of 33/sup 0/, 54/sup 0/, 70/sup 0/ and 90/sup 0/. The energy spread of the incident electron beam is estimated to be typically 25 meV FWHM. In addition to the /sup 1/S and /sup 3/P resonances which have been reported in earlier studies, a /sup 1/D resonance can be clearly seen and there is some evidence of a resonance state at a higher energy, probably corresponding to a /sup 1/S resonance state. The energies and resonance widths of all these features have been determined.

  7. Inelastic cross sections for positron scattering from atomic hydrogen

    International Nuclear Information System (INIS)

    Positronium formation (Ps) cross sections for positrons impinging on atomic hydrogen were measured in the impact energy range from 13eV to 255eV at the High Intensity Positron (HIP) beam at Brookhaven National Laboratory (BNL). The Ps-formation cross section was found to rise rapidly from the threshold at 6.8eV to a maximum value of (2.98 ± 0.18) x 10-16 cm2 for ∼ 15eV positrons. By 75eV it drops below the detection limit of 0.17 x 10-16 cm2 which is the present level of statistical uncertainty. The experiment was modified to enable the measurement of doubly differential scattering cross sections

  8. Resonance structure in elastic scattering of electrons from atomic hydrogen

    International Nuclear Information System (INIS)

    High-energy-resolution spectra of electrons scattered elastically from atomic hydrogen have been obtained for incident electron energies of 9.2-10.4 eV and at angles of 330, 540, 700 and 900. The energy spread of the incident electron beam is estimated to be typically 25 meV FWHM. In addition to the 1S and 3P resonances which have been reported in earlier studies, a 1D resonance can be clearly seen and there is some evidence of a resonance state at a higher energy, probably corresponding to a 1S resonance state. The energies and resonance widths of all these features have been determined. (author)

  9. Inelastic cross sections for positron scattering from atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Weber, M.; Hofmann, A.; Raith, W.; Sperber, W. [Bielefeld Univ. (Germany). Fakultaet fuer Physik; Jacobsen, F.; Lynn, K.G. [Brookhaven National Lab., Upton, NY (United States)

    1994-12-31

    Positronium formation (Ps) cross sections for positrons impinging on atomic hydrogen were measured in the impact energy range from 13eV to 255eV at the High Intensity Positron (HIP) beam at Brookhaven National Laboratory (BNL). The Ps-formation cross section was found to rise rapidly from the threshold at 6.8eV to a maximum value of (2.98 {plus_minus} 0.18) {times} 10{sup {minus}16} cm{sup 2} for {approx} 15eV positrons. By 75eV it drops below the detection limit of 0.17 {times} 10{sup {minus}16} cm{sup 2} which is the present level of statistical uncertainty. The experiment was modified to enable the measurement of doubly differential scattering cross sections.

  10. Dirac equation in very special relativity for hydrogen atom

    Energy Technology Data Exchange (ETDEWEB)

    Maluf, R.V., E-mail: r.v.maluf@fisica.ufc.br [Universidade Federal do Ceará (UFC), Departamento de Física, Campus do Pici, Caixa Postal 6030, 60455-760 Fortaleza, Ceará (Brazil); Silva, J.E.G., E-mail: euclides@fisica.ufc.br [Universidade Federal do Ceará (UFC), Departamento de Física, Campus do Pici, Caixa Postal 6030, 60455-760 Fortaleza, Ceará (Brazil); Cruz, W.T., E-mail: wilamicruz@gmail.com [Instituto Federal de Educação, Ciência e Tecnologia do Ceará (IFCE), Campus Juazeiro do Norte, 63040-000 Juazeiro do Norte, Ceará (Brazil); Almeida, C.A.S., E-mail: carlos@fisica.ufc.br [Universidade Federal do Ceará (UFC), Departamento de Física, Campus do Pici, Caixa Postal 6030, 60455-760 Fortaleza, Ceará (Brazil)

    2014-11-10

    In this work, we study the modified Dirac equation in the framework of very special relativity (VSR). The low-energy regime is accessed and the nonrelativistic Hamiltonian is obtained. It turns out that this Hamiltonian is similar to that achieved from the Standard Model Extension (SME) via coupling of the spinor field to a Lorentz-violating term, but new features arise inherited from the non-local character of the VSR. In addition, the implications of the VSR-modified Lorentz symmetry on the spectrum of a hydrogen atom are determined by calculating the first-order energy corrections in the context of standard quantum mechanics. Among the results, we highlight that the modified Hamiltonian provides non-vanishing corrections which lift the degeneracy of the energy levels and allow us to find an upper bound upon the VSR-parameter.

  11. Dirac equation in very special relativity for hydrogen atom

    Directory of Open Access Journals (Sweden)

    R.V. Maluf

    2014-11-01

    Full Text Available In this work, we study the modified Dirac equation in the framework of very special relativity (VSR. The low-energy regime is accessed and the nonrelativistic Hamiltonian is obtained. It turns out that this Hamiltonian is similar to that achieved from the Standard Model Extension (SME via coupling of the spinor field to a Lorentz-violating term, but new features arise inherited from the non-local character of the VSR. In addition, the implications of the VSR-modified Lorentz symmetry on the spectrum of a hydrogen atom are determined by calculating the first-order energy corrections in the context of standard quantum mechanics. Among the results, we highlight that the modified Hamiltonian provides non-vanishing corrections which lift the degeneracy of the energy levels and allow us to find an upper bound upon the VSR-parameter.

  12. On the energy levels of the hydrogen atom

    CERN Document Server

    Fewster, C J

    1993-01-01

    We re-examine the justification for the imposition of regular boundary conditions on the wavefunction at the Coulomb singularity in the treatment of the hydrogen atom in non-relativistic quantum mechanics. We show that the issue of the correct boundary conditions is not independent of the physical structure of the proton. Under the physically reasonable assumption that the finite size and structure of the proton can be represented as a positive correction to the Coulomb potential, we give a justification for the regular boundary condition, which, in contrast to the usual treatments, is physically motivated and mathematically rigorous. We also describe how irregular boundary conditions can be used to model non-positive corrections to the Coulomb potential.

  13. Phase Space Structures Explain Hydrogen Atom Roaming in Formaldehyde Decomposition.

    Science.gov (United States)

    Mauguière, Frédéric A L; Collins, Peter; Kramer, Zeb C; Carpenter, Barry K; Ezra, Gregory S; Farantos, Stavros C; Wiggins, Stephen

    2015-10-15

    We re-examine the prototypical roaming reaction--hydrogen atom roaming in formaldehyde decomposition--from a phase space perspective. Specifically, we address the question "why do trajectories roam, rather than dissociate through the radical channel?" We describe and compute the phase space structures that define and control all possible reactive events for this reaction, as well as provide a dynamically exact description of the roaming region in phase space. Using these phase space constructs, we show that in the roaming region, there is an unstable periodic orbit whose stable and unstable manifolds define a conduit that both encompasses all roaming trajectories exiting the formaldehyde well and shepherds them toward the H2···CO well. PMID:26499774

  14. Effects of atomic hydrogen and deuterium exposure on high polarization GaAs photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    M. Baylac; P. Adderley; J. Brittian; J. Clark; T. Day; J. Grames; J. Hansknecht; M. Poelker; M. Stutzman; A. T. Wu; A. S. Terekhov

    2005-12-01

    Strained-layer GaAs and strained-superlattice GaAs photocathodes are used at Jefferson Laboratory to create high average current beams of highly spin-polarized electrons. High electron yield, or quantum efficiency (QE), is obtained only when the photocathode surface is atomically clean. For years, exposure to atomic hydrogen or deuterium has been the photocathode cleaning technique employed at Jefferson Laboratory. This work demonstrates that atomic hydrogen cleaning is not necessary when precautions are taken to ensure that clean photocathode material from the vendor is not inadvertently dirtied while samples are prepared for installation inside photoemission guns. Moreover, this work demonstrates that QE and beam polarization can be significantly reduced when clean high-polarization photocathode material is exposed to atomic hydrogen from an rf dissociator-style atomic hydrogen source. Surface analysis provides some insight into the mechanisms that degrade QE and polarization due to atomic hydrogen cleaning.

  15. Transient absorption spectra of the laser-dressed hydrogen atom

    Science.gov (United States)

    Murakami, Mitsuko; Chu, Shih-I.

    2013-10-01

    We present a theoretical study of transient absorption spectra of laser-dressed hydrogen atoms, based on numerical solutions of the time-dependent Schrödinger equation. The timing of absorption is controlled by the delay between an extreme ultra violet (XUV) pulse and an infrared (IR) laser field. The XUV pulse is isolated and several hundred attoseconds in duration, which acts as a pump to drive the ground-state electron to excited p states. The subsequent interaction with the IR field produces dressed states, which manifest as sidebands between the 1s-np absorption spectra separated by one IR-photon energy. We demonstrate that the population of dressed states is maximized when the timing of the XUV pulse coincides with the zero crossing of the IR field, and that their energies can be manipulated in a subcycle time scale by adding a chirp to the IR field. An alternative perspective to the problem is to think of the XUV pulse as a probe to detect the dynamical ac Stark shifts. Our results indicate that the accidental degeneracy of the hydrogen excited states is removed while they are dressed by the IR field, leading to large ac Stark shifts. Furthermore, we observe the Autler-Townes doublets for the n=2 and 3 levels using the 656 nm dressing field, but their separation does not agree with the prediction by the conventional three-level model that neglects the dynamical ac Stark shifts.

  16. Atomic scale simulations of hydrogen implantation defects in hydrogen implanted silicon - smart Cut technology

    International Nuclear Information System (INIS)

    The topic of this thesis is related to the implantation step of the SmartCutTM technology. This technology uses hydrogen in order to transfer silicon layers on insulating substrates. The transfer is performed through a fracture induced by the formation of bidimensional defects well known in literature as 'platelets'. More exactly, we have studied within this thesis work the defects appearing in the post implant state and the evolution of the implantation damage towards a state dominated by platelets. The study is organised into two parts: in the first part we present the results obtained by atomic scale simulations while in the second part we present an infrared spectroscopy study of the evolution of defects concentrations after annealing at different temperatures. The atomic scale simulations have been performed within the density functional theory and they allowed us to compute the formation energies and the migration and recombination barriers. The defects included in our study are: the atomic and diatomic interstitials, the hydrogenated vacancies and multi-vacancies and the several platelets models. The obtained energies allowed us to build a stability hierarchy for these types of defects. This scheme has been confronted with some infrared analysis on hydrogen implanted silicon samples (37 keV) in a sub-dose regime which does not allow usually the formation of platelets during the implantation step. The analysis of the infrared data allowed the detailed description of the defects concentration based on the behaviour of peaks corresponding to the respective defects during annealing. The comparison between these evolutions and the energy scheme obtained previously allowed the validation of an evolution scenario of defects towards the platelet state. (author)

  17. Correlation of Hydrogen-Atom Abstraction Reaction Efficiencies for Aryl Radicals with their Vertical Electron Affinities and the Vertical Ionization Energies of the Hydrogen Atom Donors

    OpenAIRE

    Jing, Linhong; Nash, John J.; Kenttämaa, Hilkka I.

    2008-01-01

    The factors that control the reactivities of aryl radicals toward hydrogen-atom donors were studied by using a dual-cell Fourier-transform ion cyclotron resonance mass spectrometer (FT – ICR). Hydrogen-atom abstraction reaction efficiencies for two substrates, cyclohexane and isopropanol, were measured for twenty-three structurally different, positively-charged aryl radicals, which included dehydrobenzenes, dehydronaphthalenes, dehydropyridines, and dehydro(iso)quinolines. A logarithmic corre...

  18. Quantum dynamics of hydrogen atoms on graphene. II. Sticking

    Energy Technology Data Exchange (ETDEWEB)

    Bonfanti, Matteo, E-mail: matteo.bonfanti@unimi.it [Dipartimento di Chimica, Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Jackson, Bret [Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003 (United States); Hughes, Keith H. [School of Chemistry, Bangor University, Bangor, Gwynedd LL57 2UW (United Kingdom); Burghardt, Irene [Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main (Germany); Martinazzo, Rocco, E-mail: rocco.martinazzo@unimi.it [Dipartimento di Chimica, Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Istituto di Scienze e Tecnologie Molecolari, Consiglio Nazionale delle Richerche, v. Golgi 19, 20133 Milano (Italy)

    2015-09-28

    Following our recent system-bath modeling of the interaction between a hydrogen atom and a graphene surface [Bonfanti et al., J. Chem. Phys. 143, 124703 (2015)], we present the results of converged quantum scattering calculations on the activated sticking dynamics. The focus of this study is the collinear scattering on a surface at zero temperature, which is treated with high-dimensional wavepacket propagations with the multi-configuration time-dependent Hartree method. At low collision energies, barrier-crossing dominates the sticking and any projectile that overcomes the barrier gets trapped in the chemisorption well. However, at high collision energies, energy transfer to the surface is a limiting factor, and fast H atoms hardly dissipate their excess energy and stick on the surface. As a consequence, the sticking coefficient is maximum (∼0.65) at an energy which is about one and half larger than the barrier height. Comparison of the results with classical and quasi-classical calculations shows that quantum fluctuations of the lattice play a primary role in the dynamics. A simple impulsive model describing the collision of a classical projectile with a quantum surface is developed which reproduces the quantum results remarkably well for all but the lowest energies, thereby capturing the essential physics of the activated sticking dynamics investigated.

  19. Quantum dynamics of hydrogen atoms on graphene. II. Sticking.

    Science.gov (United States)

    Bonfanti, Matteo; Jackson, Bret; Hughes, Keith H; Burghardt, Irene; Martinazzo, Rocco

    2015-09-28

    Following our recent system-bath modeling of the interaction between a hydrogen atom and a graphene surface [Bonfanti et al., J. Chem. Phys. 143, 124703 (2015)], we present the results of converged quantum scattering calculations on the activated sticking dynamics. The focus of this study is the collinear scattering on a surface at zero temperature, which is treated with high-dimensional wavepacket propagations with the multi-configuration time-dependent Hartree method. At low collision energies, barrier-crossing dominates the sticking and any projectile that overcomes the barrier gets trapped in the chemisorption well. However, at high collision energies, energy transfer to the surface is a limiting factor, and fast H atoms hardly dissipate their excess energy and stick on the surface. As a consequence, the sticking coefficient is maximum (∼0.65) at an energy which is about one and half larger than the barrier height. Comparison of the results with classical and quasi-classical calculations shows that quantum fluctuations of the lattice play a primary role in the dynamics. A simple impulsive model describing the collision of a classical projectile with a quantum surface is developed which reproduces the quantum results remarkably well for all but the lowest energies, thereby capturing the essential physics of the activated sticking dynamics investigated. PMID:26429029

  20. Photo-Ionization of Hydrogen Atom in a Circularly Polarized Standing Electromagnetic Wave

    Institute of Scientific and Technical Information of China (English)

    LIU Xiang-Tao; ZHANG Qi-Ren; WANG Wan-Zhang

    2004-01-01

    Applying time-independent non-perturbative formalism to the photo-ionization of hydrogen atom immersed in a strong circularly polarized standing electromagnetic wave, we calculate the shift of energy levels and the distortion of wave functions for the hydrogen atom, the ionization cross section induced by the standing wave, and the angular distribution of photoelectrons and obtain some interesting results.

  1. Explicit expressions and recurrence formulas of radial average value for N-dimensional hydrogen atom

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    In this paper, two recurrence formulas for radial average values of N-dimensional hydrogen atom are derived. Explicit results can be applied to discuss average value of centrifugal potential energy and other physical quantities. The relevant results of the usual hydrogen atom are contained in more general conclusion of this paper as special cases.

  2. The structures and dynamics of atomic and molecular adsorbates on metal surfaces by scanning tunneling microscopy and low energy electron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Hyungsuk Alexander

    1996-12-01

    Studies of surface structure and dynamics of atoms and molecules on metal surfaces are presented. My research has focused on understanding the nature of adsorbate-adsorbate and adsorbate-substrate interactions through surface studies of coverage dependency and coadsorption using both scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The effect of adsorbate coverage on the surface structures of sulfur on Pt(111) and Rh(111) was examined. On Pt(111), sulfur forms p(2x2) at 0.25 ML of sulfur, which transforms into a more compressed ({radical}3x{radical}3)R30{degrees} at 0.33 ML. On both structures, it was found that sulfur adsorbs only in fcc sites. When the coverage of sulfur exceeds 0.33 ML, it formed more complex c({radical}3x7)rect structure with 3 sulfur atoms per unit cell. In this structure, two different adsorption sites for sulfur atoms were observed - two on fcc sites and one on hcp site within the unit cell.

  3. Symmetry-resolved spectroscopy by detection of a metastable hydrogen atom for investigating the doubly excited states of molecular hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Odagiri, Takeshi; Kumagai, Yoshiaki; Tanabe, Takehiko; Nakano, Motoyoshi; Kouchi, Noriyuki [Department of Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan); Suzuki, Isao H, E-mail: joe@chem.titech.ac.j [Photon Factory, IMSS, KEK, Tsukuba, Ibaraki 305-0801 (Japan)

    2009-11-01

    Symmetry-resolved spectroscopy for investigating the doubly excited states of molecular hydrogen has been newly developed, where a metastable hydrogen atom dissociating in a direction parallel and perpendicular to the electric vector of the linearly polarized incident light is detected.

  4. Atom-hydrogen energy and influence of transport pollution to the environment

    International Nuclear Information System (INIS)

    Full text : The justification of feasibility of atomic-hydrogen energy is important to take into consideration of the results of comparative analysis of environmental impact of combustion of organic fuels and hydrogen. The use of gasoline, natural gas and hydrogen in the transport sector leads to various impacts on environment. The assessment of environmental impact

  5. HYDROGEN PEROXIDE BLEACHING OF HARDWOOD KRAFT PULP WITH ADSORBED BIRCH XYLAN AND ITS EFFECT ON PAPER PROPERTIES

    Directory of Open Access Journals (Sweden)

    Hyejung Youn

    2011-02-01

    Full Text Available The adsorption of xylan on pulp fibers improves the strength properties of paper. However, the optical properties are decreased significantly. The objective of our research was to bleach hardwood kraft pulp with adsorbed birch xylan by hydrogen peroxide and study the effect of bleaching parameters on paper properties. The bleaching parameters studied included bleaching temperature, time, initial pH as well as MgSO4 dosage. The optical properties (whiteness, brightness, opacity and physical properties (tensile index, tearing index, bulk of handsheets made from the pulp bleached with different process variables were measured. The results showed that better optical properties were obtained with higher bleaching temperature, longer bleaching time, and more MgSO4 dosage. Bleaching from an initial pH of 11 provided the highest brightness value. On the other hand, strength properties were improved with decreasing of the bleaching temperature, and increasing the initial pH and MgSO4 dosage. The relationship between strength properties and bleaching time varied depending on bleaching temperature. According to the results, both good mechanical properties and optical properties could be achieved when the operating parameters were controlled properly. Therefore hydrogen peroxide bleaching was proved to be a suitable method for bleaching hardwood kraft pulp with adsorption of birch xylan.

  6. New horizons in chemical propulsion. [processes using free radicals, atomic hydrogen, excited species, etc

    Science.gov (United States)

    Cohen, W.

    1973-01-01

    After a review of the work of the late-Fifties on free radicals for propulsion, it is concluded that atomic hydrogen would provide a potentially large increase in specific impulse. Work conducted to find an approach for isolating atomic hydrogen is considered. Other possibilities for obtaining propellants of greatly increased capability might be connected with the technology for the generation of activated states of gases, metallic hydrogen, fuels obtained from other planets, and laser transfer of energy.

  7. Measurement of diffusion process of iron atoms under high pressure of hydrogen by time-domain analysis of nuclear resonant scattering of X-rays

    International Nuclear Information System (INIS)

    We applied the time-domain analysis of nuclear resonant scattering (NRS) of X-rays for the study of the hydrogen-induced enhancement of atomic diffusion. The time-domain analysis of NRS is a powerful technique for studying diffusion processes on an atomic scale. The NRS measurement combined with high-pressure technique enables the direct measurement of self-diffusion processes under high hydrogen pressures. In this preliminary experiment, self-diffusion in 4 μm thick 57Fe foils at 0.8 GPa was investigated. The samples of the 57Fe were encapsulated with MgO or NaCl. Faster decays caused by diffusion of Fe atoms were observed in the time spectra of NRS at high temperatures. This enhancement of diffusion is believed to be the hydrogen-induced effect. In the present experiment, hydrogen should have been supplied to the samples by reaction with water originally adsorbed on NaCl/MgO powder particles. It was concluded that the diffusion of 57Fe atoms under high pressure can be studied by nuclear resonant scattering of X-rays using a compact cubic-anvil press. The NRS method can also be extended to the study of atomic diffusion in the subsurface region by doping 57Fe layer(s) at known depths.

  8. The role of adsorbed hydrogen species in the dehydrogenation and hydrocracking of saturated hydrocarbons on supported metal catalysts

    Science.gov (United States)

    Babenkova, L. V.; Naidina, I. N.

    1994-07-01

    The role of certain hydrogen absorption complexes in the dehydrogenation and hydrocracking of hydrocarbons on low-percentage one-component, (Pt, Pd/Al2O3) and bimetallic (Pd-Co, Pd-Ce, Pt-Co, Pt-Sn/Al2O3) catalysts is discussed. It is shown that the combination of metals in reduced forms and forms oxidised to different extents on the catalyst surfaces is responsible for their high capacity for the chemisorption of hydrogen, the wide range of its energetic inhomogeneity, and the high activity of the catalysts in the conversion of saturated hydrocarbons. Catalysts containing on the surface mainly sites for the type Hδ- chemisorption are the most active in the dehydrogenation of hydrocarbons, whereas specimens chemisorbing hydrogen mainly in the Hδ+ form are the most active in the hydrockracking of hydrocarbons. It is concluded that the strongly bound atomic hydrogen Hδ+ plays a dual role, since it not only participates directly in the dehydrogenation reaction but also promotes the reduction of the electron-deficient surface centres, which optimises the number of centres for the activation of C-H bonds. The bibliography includes 75 references.

  9. Subharmonic excitation in amplitude modulation atomic force microscopy in the presence of adsorbed water layers

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Sergio [Laboratory of Energy and Nanosciences, Masdar Institute of Science and Technology, P.O. BOX 54224, Abu Dhabi (United Arab Emirates); Barcons, Victor [Departament de Disseny i Programacio de Sistemes Electronics, UPC - Universitat Politecnica de Catalunya Av. Bases, 61, 08242 Manresa (Spain); Verdaguer, Albert [Centre d' Investigacio en Nanociencia i Nanotecnologia (CIN2) (CSIC-ICN), Esfera UAB, Campus de la UAB, Edifici CM-7, 08193-Bellaterra, Catalunya (Spain); Chiesa, Matteo [Laboratory of Energy and Nanosciences, Masdar Institute of Science and Technology, P.O. BOX 54224, Abu Dhabi (United Arab Emirates); Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307 (United States)

    2011-12-01

    In ambient conditions, nanometric water layers form on hydrophilic surfaces covering them and significantly changing their properties and characteristics. Here we report the excitation of subharmonics in amplitude modulation atomic force microscopy induced by intermittent water contacts. Our simulations show that there are several regimes of operation depending on whether there is perturbation of water layers. Single period orbitals, where subharmonics are never induced, follow only when the tip is either in permanent contact with the water layers or in pure noncontact where the water layers are never perturbed. When the water layers are perturbed subharmonic excitation increases with decreasing oscillation amplitude. We derive an analytical expression which establishes whether water perturbations compromise harmonic motion and show that the predictions are in agreement with numerical simulations. Empirical validation of our interpretation is provided by the observation of a range of values for apparent height of water layers when subharmonic excitation is predicted.

  10. The dynamical properties of a Rydberg hydrogen atom between two parallel metal surfaces

    Institute of Scientific and Technical Information of China (English)

    Liu Wei; Li Hong-Yun; Yang Shan-Ying; Lin Sheng-Lu

    2011-01-01

    This paper presents the dynamical properties of a Rydberg hydrogen atom between two metal surfaces using phase space analysis methods. The dynamical behaviour of the excited hydrogen atom depends sensitively on the atom-surface distance d. There exists a critical atom-surface distance dc = 1586 a.u. When the atom-surface distance d is larger than the critical distance dc, the image charge potential is less important than the Coulomb potential, the system is near-integrable and the electron motion is regular. As the distance d decreases, the system will tend to be non-integrable and unstable, and the electron might be captured by the metal surfaces.

  11. Separation of Rebaudiana A from Steviol glycoside using a polymeric adsorbent with multi-hydrogen bonding in a non-aqueous system.

    Science.gov (United States)

    Ba, Jing; Zhang, Na; Yao, Lijuan; Ma, Ning; Wang, Chunhong

    2014-11-15

    Rebaudioside A (RA) and stevioside (SS) are the primary effective glycoside components in Stevia Rebaudiana. The RA glycoside is sweeter, and it tastes similarly to sucrose. Because extracts with a high RA content can be used as natural sweeteners for food additives approved by the FAO and FDA, RA should generate high market demand. In this study, an efficient method for separating RA was established based on the synergistic multi-hydrogen bonding interaction between a polymeric adsorbent and the RA glycoside. To overcome the destruction of the hydrophobic affinity required for the selective adsorption of RA, an innovative non-aqueous environment was established for adsorption and separation. To this end, an initial polymeric adsorbent composed of a glycidyl methacrylate and trimethylolpropane trimethacrylate (GMA-co-TMPTMA) copolymer matrix was synthesized, and polyethylene polyamine was employed as a functional reagent designed to react with the epoxy group on GME-co-TMPTMA to form a highly selective macroporous adsorbent. The effects of the different functional reagents and the solvent polarity on the adsorption selectivity for RA and SS, respectively, were investigated. Matching the structure of the polyethylene polyamine and sugar ligand on the glycoside molecule was essential in ensuring that the maximum synergistic interaction between adsorbent and adsorbate would be achieved. Moreover, the hydrogen-bonding force was observed to increase when the polarity of the adsorption solvent decreased. Therefore, among the synthesized macroporous polymeric adsorbents, the GTN4 adsorbent-bonding tetraethylenepentamine functional group provided the best separation in an n-butyl alcohol solution. Under the optimized gradient elution conditions, RA and SS can be effectively separated, and the contents of RA and SS increased from 33.5% and 51.5% in the initial crude extract to 95.4% and 78.2% after separation, respectively. Compared to conventional methods, the adsorption

  12. General model of depolarization and transfer of polarization of singly ionized atoms by collisions with hydrogen atoms

    CERN Document Server

    Derouich, Moncef

    2016-01-01

    Simulations of the generation of the atomic polarization is necessary for interpreting the second solar spectrum. For this purpose, it is important to rigorously determine the effects of the isotropic collisions with neutral hydrogen on the atomic polarization of the neutral atoms, ionized atoms and molecules. Our aim is to treat in generality the problem of depolarizing isotropic collisions between singly ionized atoms and neutral hydrogen in its ground state. Using our numerical code, we computed the collisional depolarization rates of the $p$-levels of ions for large number of values of the effective principal quantum number $n^{*}$ and the Uns\\"old energy $E_p$. Then, genetic programming has been utilized to fit the available depolarization rates. As a result, strongly non-linear relationships between the collisional depolarization rates, $n^{*}$ and $E_p$ are obtained, and are shown to reproduce the original data with accuracy clearly better than 10\\%. These relationships allow quick calculations of the ...

  13. Analytical Absorption Cross-Section for Photon by a Hydrogen 2s Atom

    Institute of Scientific and Technical Information of China (English)

    Boniface Otieno Ndinya; Stephen Onyango Okeyo

    2011-01-01

    We calculate the absorption cross-section for photon by a hydrogen 2s atom using the quantum-classical approximation for the total photo cross-section of many electron atoms.With the application of the first-order term of the Baker-Hausdorf expansion, the absorption cross-section for the hydrogen 2s atom decreases to a minimum, the Cooper pair minimum, at low photon energy.Such a minimum is absent in the exact absorption cross-section for photon by a hydrogen 2s atom.We have extended the calculation for the absorption cross-section of the hydrogen 2s atom using the quantum-classical approximation for the total photo cross-section of many electron to include the second-order term of the Baker-Hausdorf expansion and observed a great reduction in the dip associated with the Cooper pair minimum at the zero crossing.

  14. An atomic hydrogen beam to test ASACUSA’s apparatus for antihydrogen spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Diermaier, M., E-mail: martin.diermaier@oeaw.ac.at; Caradonna, P.; Kolbinger, B. [Austrian Academy of Sciences, Stefan Meyer Institute for Subatomic Physics (Austria); Malbrunot, C. [CERN (Switzerland); Massiczek, O.; Sauerzopf, C.; Simon, M. C.; Wolf, M.; Zmeskal, J.; Widmann, E. [Austrian Academy of Sciences, Stefan Meyer Institute for Subatomic Physics (Austria)

    2015-08-15

    The ASACUSA collaboration aims to measure the ground state hyperfine splitting (GS-HFS) of antihydrogen, the antimatter counterpart to atomic hydrogen. Comparisons of the corresponding transitions in those two systems will provide sensitive tests of the CPT symmetry, the combination of the three discrete symmetries charge conjugation, parity, and time reversal. For offline tests of the GS-HFS spectroscopy apparatus we constructed a source of cold polarised atomic hydrogen. In these proceedings we report the successful observation of the hyperfine structure transitions of atomic hydrogen with our apparatus in the earth’s magnetic field.

  15. Tunable Adsorption and Desorption of Hydrogen Atoms on Single-Walled Carbon Nanotubes

    Institute of Scientific and Technical Information of China (English)

    赵明文; 夏日源; 马玉臣; 英敏菊; 刘向东; 梅良模

    2002-01-01

    Chemical adsorption and desorption of hydrogen atoms on single-walled carbon nanotubes (SWNTs) are investi-gated by using molecular dynamics simulations. It is found that the adsorption and desorption energy of hydrogenatoms depend on the hydrogen coverage and the diameter of the SWNTs. Hydrogen-adsorption geometry at thecoverage of 1.0 is more energetically stable. The adsorption energy decreases with the increasing diameter ofthe armchair tubes. The adsorption and desorption energy of hydrogen atoms can be modified reversibly byexternally radial deformation. The averaged C-H bond energy on the high curvature sites of the deformed tubeincreases with increasing radial deformation, while that on the low curvature sites decreases.

  16. Signatures of Quantum-Tunneling Diffusion of Hydrogen Atoms on Water Ice at 10 K.

    Science.gov (United States)

    Kuwahata, K; Hama, T; Kouchi, A; Watanabe, N

    2015-09-25

    Reported here is the first observation of the tunneling surface diffusion of a hydrogen (H) atom on water ice. Photostimulated desorption and resonance-enhanced multiphoton ionization methods were used to determine the diffusion rates at 10 K on amorphous solid water and polycrystalline ice. H-atom diffusion on polycrystalline ice was 2 orders of magnitude faster than that of deuterium atoms, indicating the occurrence of tunneling diffusion. Whether diffusion is by tunneling or thermal hopping also depends on the diffusion length of the atoms and the morphology of the surface. Our findings contribute to a better understanding of elementary physicochemical processes of hydrogen on cosmic ice dust. PMID:26451552

  17. The effects of atomic hydrogen and flake on mechanical properties of a tyre steel

    International Nuclear Information System (INIS)

    The effects of hydrogen and flake on the fracture toughness, hydrogen-induced delayed cracking (HIDC), impact toughness and fatigue properties of a tyre steel have been investigated. The results showed that there was no effect of flake and atomic hydrogen on the fracture toughness KIC. Atomic hydrogen could induce delayed failure under constant displacement. The threshold stress intensity factor of hydrogen-induced delayed cracking, KIH, decreased linearly with diffusible hydrogen concentration C0, i.e., KIH (MPa m1/2) = KIC - 4.0C0 (ppm) (C0 > 0.5 ppm). Atomic hydrogen had no effect on impact toughness and fatigue properties when the C0 was low (C0 ≤ 0.5 ppm). The flakes decreased impact toughness and caused it to fluctuate. Atomic hydrogen increased the fatigue crack growth rate when the diffusible hydrogen concentration was high enough (C0 ≥ 2.5 ppm). The flakes increased and undulated the fatigue crack growth rate

  18. Schwinger variational calculation of ionization of hydrogen atoms for large momentum transfers

    Indian Academy of Sciences (India)

    K Chakrabarti

    2002-03-01

    Schwinger variational principle is used here to study large momentum transfer cases of electron and positron impact ionization of atomic hydrogen from the ground state at intermediate and moderately high energies. The results appear somewhat better compared to other theories.

  19. Does God Play Dice with Universe The Hydrogen Atomic Model of Bohr and de Broglie

    CERN Document Server

    Kamenov, P S

    1999-01-01

    In this paper it is shown that if one accept assumption of de Broglie that "unitary wave-particle" exists simultaneously and this coexistence is real, then one can find the mean life time of the hydrogen atom of Bohr (intensities). Something more, the acceptance of de Broglie's ideas show that a single excited hydrogen atom decays at exactly predictable moment (after excitation). The natural width of excited hydrogen atoms are found using the Bohr's model of this atom and de Broglie's ideas. The mean life time of the excited states is a characteristic only of a statistical ensemble of many atoms and coincide exactly with experimental data and can be used for analytical applications. It is shown also that resonant Mossbauer absorption in time domain provides a qualitative evidence of the existence of "own lifetime" for first excited states of the nuclei.

  20. Fluorescence (TALIF) measurement of atomic hydrogen concentration in a coplanar surface dielectric barrier discharge

    Science.gov (United States)

    Mrkvičková, M.; Ráheľ, J.; Dvořák, P.; Trunec, D.; Morávek, T.

    2016-10-01

    Spatially and temporally resolved measurements of atomic hydrogen concentration above the dielectric of coplanar barrier discharge are presented for atmospheric pressure in 2.2% H2/Ar. The measurements were carried out in the afterglow phase by means of two-photon absorption laser-induced fluorescence (TALIF). The difficulties of employing the TALIF technique in close proximity to the dielectric surface wall were successfully addressed by taking measurements on a suitable convexly curved dielectric barrier, and by proper mathematical treatment of parasitic signals from laser-surface interactions. It was found that the maximum atomic hydrogen concentration is situated closest to the dielectric wall from which it gradually decays. The maximum absolute concentration was more than 1022 m-3. In the afterglow phase, the concentration of atomic hydrogen above the dielectric surface stays constant for a considerable time (10 μs-1 ms), with longer times for areas situated farther from the dielectric surface. The existence of such a temporal plateau was explained by the presented 1D model: the recombination losses of atomic hydrogen farther from the dielectric surface are compensated by the diffusion of atomic hydrogen from regions close to the dielectric surface. The fact that a temporal plateau exists even closest to the dielectric surface suggests that the dielectric surface acts as a source of atomic hydrogen in the afterglow phase.

  1. Continuum effects on positron scattering of atomic hydrogen at intermediate energies

    Energy Technology Data Exchange (ETDEWEB)

    Ratnavelu, Kuru [Quantum Scattering Theory Group, Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia). E-mail: j2kurun at umcsd.um.edu.my; Rajagopal, Kalai Kumar [Quantum Scattering Theory Group, Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    1999-07-28

    An optical potential method to study the positron-hydrogen atom scattering system within the close-coupling framework that includes both the positron-hydrogen and positronium-proton channels has been implemented. Ionization, positronium formation and total cross sections are reported and are compared to other available theoretical and experimental data. (author00.

  2. Fracture mechanism of TiAl intermetallics caused by hydride and atomic hydrogen

    Institute of Scientific and Technical Information of China (English)

    高克玮; 王燕斌; 林志; 乔利杰; 褚武扬

    1999-01-01

    Hydrogen embrittlement (HE) of TiAl intermetallics was studied at room temperature. The results showed that there were two forms of HE in TiAl intermetallics, i.e. hydride HE and atomic HE. Most of hydrogen in TiAl intermetallics was transformed into hydrides at room temperature. The hydride exists as (TiAl)Hx for a low hydrogen concentration while it exists in several forms for a higher hydrogen concentration. Stress intensity factor KIC decreased with increase in hydride concentration. KIC decreased further when TiAl intermetallics were charged cathodically with hydrogen in 1 mol/L H2SO4 solution. Stress intensity factor during hydrogen charging KIH was about 50% KIC. 20% of the decrease was caused by hydrides while 30% was caused by atomic hydrogen. Mechanism of HE caused hydrides was the same as any other second phase in nature. Delayed fracture caused by atomic hydrogen resulted from hydrogen induced local plastic deformation.

  3. Hydrogen atoms can be located accurately and precisely by x-ray crystallography.

    Science.gov (United States)

    Woińska, Magdalena; Grabowsky, Simon; Dominiak, Paulina M; Woźniak, Krzysztof; Jayatilaka, Dylan

    2016-05-01

    Precise and accurate structural information on hydrogen atoms is crucial to the study of energies of interactions important for crystal engineering, materials science, medicine, and pharmacy, and to the estimation of physical and chemical properties in solids. However, hydrogen atoms only scatter x-radiation weakly, so x-rays have not been used routinely to locate them accurately. Textbooks and teaching classes still emphasize that hydrogen atoms cannot be located with x-rays close to heavy elements; instead, neutron diffraction is needed. We show that, contrary to widespread expectation, hydrogen atoms can be located very accurately using x-ray diffraction, yielding bond lengths involving hydrogen atoms (A-H) that are in agreement with results from neutron diffraction mostly within a single standard deviation. The precision of the determination is also comparable between x-ray and neutron diffraction results. This has been achieved at resolutions as low as 0.8 Å using Hirshfeld atom refinement (HAR). We have applied HAR to 81 crystal structures of organic molecules and compared the A-H bond lengths with those from neutron measurements for A-H bonds sorted into bonds of the same class. We further show in a selection of inorganic compounds that hydrogen atoms can be located in bridging positions and close to heavy transition metals accurately and precisely. We anticipate that, in the future, conventional x-radiation sources at in-house diffractometers can be used routinely for locating hydrogen atoms in small molecules accurately instead of large-scale facilities such as spallation sources or nuclear reactors. PMID:27386545

  4. Hydrogen atoms can be located accurately and precisely by x-ray crystallography

    Science.gov (United States)

    Woińska, Magdalena; Grabowsky, Simon; Dominiak, Paulina M.; Woźniak, Krzysztof; Jayatilaka, Dylan

    2016-01-01

    Precise and accurate structural information on hydrogen atoms is crucial to the study of energies of interactions important for crystal engineering, materials science, medicine, and pharmacy, and to the estimation of physical and chemical properties in solids. However, hydrogen atoms only scatter x-radiation weakly, so x-rays have not been used routinely to locate them accurately. Textbooks and teaching classes still emphasize that hydrogen atoms cannot be located with x-rays close to heavy elements; instead, neutron diffraction is needed. We show that, contrary to widespread expectation, hydrogen atoms can be located very accurately using x-ray diffraction, yielding bond lengths involving hydrogen atoms (A–H) that are in agreement with results from neutron diffraction mostly within a single standard deviation. The precision of the determination is also comparable between x-ray and neutron diffraction results. This has been achieved at resolutions as low as 0.8 Å using Hirshfeld atom refinement (HAR). We have applied HAR to 81 crystal structures of organic molecules and compared the A–H bond lengths with those from neutron measurements for A–H bonds sorted into bonds of the same class. We further show in a selection of inorganic compounds that hydrogen atoms can be located in bridging positions and close to heavy transition metals accurately and precisely. We anticipate that, in the future, conventional x-radiation sources at in-house diffractometers can be used routinely for locating hydrogen atoms in small molecules accurately instead of large-scale facilities such as spallation sources or nuclear reactors.

  5. Derivation of the dipole approximation from the exact transition probabilities for hydrogen atoms

    International Nuclear Information System (INIS)

    The usual dipole approximation for the transition probabilities for hydrogen atoms is derived from the exact transition probabilities by considering j = 1 photons only, neglecting retardation, and using an identity derived from the wave equation for the radial wave function for the atom

  6. Ionization of highly excited hydrogen atoms by a circularly polarized microwave field

    Energy Technology Data Exchange (ETDEWEB)

    Zakrzewski, J.; Delande, D.; Gay, J. (Laboratoire de Spectroscopie Hertzienne de l' Ecole Normale Superieure, Universite Pierre et Marie Curie, Tour 12, 4 place Jussieu, 75252 Paris CEDEX 05 (France)); Rzazewski, K. (Centrum Fizyki Teoretycznej, Polskiej Akademii Nauk, Aleja Lotnikow 32/46, 02668 Warsaw (Poland))

    1993-04-01

    Some quantum-mechanical results describing the ionization of initially highly excited hydrogen atoms by a strong, circularly polarized microwave field are presented. A simplified two-dimensional model of the atom is used. Discrepancies between various classical estimates for the low-frequency ionization threshold are resolved.

  7. Path integral Monte Carlo simulations of H2 adsorbed to lithium-doped benzene: A model for hydrogen storage materials.

    Science.gov (United States)

    Lindoy, Lachlan P; Kolmann, Stephen J; D'Arcy, Jordan H; Crittenden, Deborah L; Jordan, Meredith J T

    2015-11-21

    Finite temperature quantum and anharmonic effects are studied in H2-Li(+)-benzene, a model hydrogen storage material, using path integral Monte Carlo (PIMC) simulations on an interpolated potential energy surface refined over the eight intermolecular degrees of freedom based upon M05-2X/6-311+G(2df,p) density functional theory calculations. Rigid-body PIMC simulations are performed at temperatures ranging from 77 K to 150 K, producing both quantum and classical probability density histograms describing the adsorbed H2. Quantum effects broaden the histograms with respect to their classical analogues and increase the expectation values of the radial and angular polar coordinates describing the location of the center-of-mass of the H2 molecule. The rigid-body PIMC simulations also provide estimates of the change in internal energy, ΔUads, and enthalpy, ΔHads, for H2 adsorption onto Li(+)-benzene, as a function of temperature. These estimates indicate that quantum effects are important even at room temperature and classical results should be interpreted with caution. Our results also show that anharmonicity is more important in the calculation of U and H than coupling-coupling between the intermolecular degrees of freedom becomes less important as temperature increases whereas anharmonicity becomes more important. The most anharmonic motions in H2-Li(+)-benzene are the "helicopter" and "ferris wheel" H2 rotations. Treating these motions as one-dimensional free and hindered rotors, respectively, provides simple corrections to standard harmonic oscillator, rigid rotor thermochemical expressions for internal energy and enthalpy that encapsulate the majority of the anharmonicity. At 150 K, our best rigid-body PIMC estimates for ΔUads and ΔHads are -13.3 ± 0.1 and -14.5 ± 0.1 kJ mol(-1), respectively. PMID:26590532

  8. Path integral Monte Carlo simulations of H2 adsorbed to lithium-doped benzene: A model for hydrogen storage materials

    Science.gov (United States)

    Lindoy, Lachlan P.; Kolmann, Stephen J.; D'Arcy, Jordan H.; Crittenden, Deborah L.; Jordan, Meredith J. T.

    2015-11-01

    Finite temperature quantum and anharmonic effects are studied in H2-Li+-benzene, a model hydrogen storage material, using path integral Monte Carlo (PIMC) simulations on an interpolated potential energy surface refined over the eight intermolecular degrees of freedom based upon M05-2X/6-311+G(2df,p) density functional theory calculations. Rigid-body PIMC simulations are performed at temperatures ranging from 77 K to 150 K, producing both quantum and classical probability density histograms describing the adsorbed H2. Quantum effects broaden the histograms with respect to their classical analogues and increase the expectation values of the radial and angular polar coordinates describing the location of the center-of-mass of the H2 molecule. The rigid-body PIMC simulations also provide estimates of the change in internal energy, ΔUads, and enthalpy, ΔHads, for H2 adsorption onto Li+-benzene, as a function of temperature. These estimates indicate that quantum effects are important even at room temperature and classical results should be interpreted with caution. Our results also show that anharmonicity is more important in the calculation of U and H than coupling—coupling between the intermolecular degrees of freedom becomes less important as temperature increases whereas anharmonicity becomes more important. The most anharmonic motions in H2-Li+-benzene are the "helicopter" and "ferris wheel" H2 rotations. Treating these motions as one-dimensional free and hindered rotors, respectively, provides simple corrections to standard harmonic oscillator, rigid rotor thermochemical expressions for internal energy and enthalpy that encapsulate the majority of the anharmonicity. At 150 K, our best rigid-body PIMC estimates for ΔUads and ΔHads are -13.3 ± 0.1 and -14.5 ± 0.1 kJ mol-1, respectively.

  9. Ionization of hydrogen atom by electron impact in the presence of elliptically polarized laser field

    International Nuclear Information System (INIS)

    The problem of ionization in electron hydrogen atom collision in the presence of elliptically polarized laser field, is investigated. The use of the higher order modification of the atomic bound state wave function shows that there is a strong enhancement in the cross section when the laser frequency is half the atomic transition frequency. The dependence of the cross section on the polarization of the laser field is also discussed. (author). 3 refs., 2 figs

  10. New results in the theory of muonic atom formation in molecular hydrogen

    International Nuclear Information System (INIS)

    Muonic atom formation in molecular hydrogen proceeds in two stages. In the first stage, the mu-molecular complex (abμe)* is formed due to Coulomb capture of a muon by a hydrogen molecule (abee), and, in the second stage, the decay of the complex leads to exotic-atom formation. We consider various channels for the decay of the complex. The main competition channels are direct dissociation and Auger decay. The primary distribution of muonic atoms over quantum states and kinetic energy has been obtained taking into account the competition of the decay channels. (orig.)

  11. Effect of atomic ordering on environmental embrittlement of (Co, Fe)3V alloy in gaseous hydrogen

    Institute of Scientific and Technical Information of China (English)

    程晓英; 万晓景

    2002-01-01

    The diffusible hydrogen contents in precharged (Co,Fe)3V alloy were measured. It is found that atomic ordering can not promote hydrogen penetration in the (Co,Fe)3V alloy. The ultimate tensile strength (UTS) and ductilities in various condition were also investigated. The results show that the UTS and elongation of disordered alloy are higher than that of ordered one with fixed diffusible hydrogen content and (Co,Fe)3V alloy with ordered structure is highly susceptible to the embrittlement in hydrogen gas. The factor which may affect the susceptibility to the embrittlement of (Co,Fe)3V alloy in h ydrogen gas is mainly due to that the atomic ordering may accelerate the kinetics of the catalytic reaction for the dissociation of molecular hydrogen into atomic hydrogen. However, it can not be roled out that atomic ordering intensifies planar slip and restricts cross-slip at the grain boundaries and enhances the susceptibility of the alloy to hydrogen embrittlement.

  12. Characterization of hot hydrogen-atom reactions by kinetic spectrography.

    Science.gov (United States)

    Tomalesky, R. E.; Sturm, J. E.

    1971-01-01

    The flash photolysis of hydrogen iodide in the presence of nitrous oxide, carbon dioxide, and water has been investigated by kinetic spectroscopy. Although the fraction of hydrogen iodide dissociated was very large, the only observable intermediate was imidogen. It was demonstrated that the rapid removal of imidogen and the apparent absence of hydroxyl radicals in each case is a result of the following two reactions, respectively: (1) NH + HI yields NH2 + I; and (2) OH + HI yields H2O + I.

  13. A compact design for a magnetic synchrotron to store beams of hydrogen atoms

    CERN Document Server

    van der Poel, Aernout P P; Softley, Timothy P; Bethlem, Hendrick L

    2015-01-01

    We present a design for an atomic synchrotron consisting of 40 hybrid magnetic hexapole lenses arranged in a circle. We show that for realistic parameters, hydrogen atoms with a velocity up to 600 m/s can be stored in a 1-meter diameter ring, which implies that the atoms can be injected in the ring directly from a pulsed supersonic beam source. This ring can be used to study collisions between stored hydrogen atoms and molecular beams of many different atoms and molecules. The advantage of using a synchrotron is two-fold: (i) the collision partners move in the same direction as the stored atoms, resulting in a small relative velocity and thus a low collision energy, and (ii) by storing atoms for many round-trips, the sensitivity to collisions is enhanced by a factor of 100-1000. In the proposed ring, the cross-sections for collisions between hydrogen, the most abundant atom in the universe, with any atom or molecule that can be put in a beam, including He, H$_2$, CO, ammonia and OH can be measured at energies...

  14. Quantification of the atomic hydrogen flux as a function of filament temperature and H2 flow rate

    NARCIS (Netherlands)

    Ugur, D.; Storm, A.J.; Verberk, R.; Brouwer, J.C.; Sloof, W.G.

    2012-01-01

    An isothermal sensor is developed to quantify the atomic hydrogen flux on a surface, which can be located at any distance from the molecular hydrogen cracking unit. This flux is determined from the measured heat effect due to recombination of atomic hydrogen at the sensor surface. The temperature of

  15. Formation of Cu, Ag and Au nanofiims under the influence of hydrogen atoms

    Directory of Open Access Journals (Sweden)

    Zhavzharov E. L.

    2015-12-01

    Full Text Available Due to their electrical properties, thin metallic films are widely used in modern micro- and nanoelectronics. These properties allow solving fundamental problems of surface and solid state physics. Up-to-date methods of producing thin films involve high vacuum or multi-stage processes, which calls for complicated equipment. The authors propose an alternative method of producing thin metallic films using atomic hydrogen. Exothermal reaction of atoms recombination in a molecule (about 4.5 eV / recombination act initiated on the solid surface by atomic hydrogen may stimulate local heating, spraying and surface atoms transfer. We investigated the process of atomic hydrogen treatment of Cu, Ag and Au metal films, obtained by thermal vacuum evaporation. There are two methods of obtaining nanofilms using atomic hydrogen treatment: sputtering and vapor-phase epitaxy. In the first method, a film is formed by reducing the thickness of the starting film. This method allows obtaining a film as thick as the monolayer. In the second method, a nanofilm is formed by deposition of metal atoms from the vapor phase. This method allows obtaining a film thickness from monolayer to ~10 nm. These methods allow creating nanofilms with controlled parameters and metal thickness. Such films would be technologically pure and have good adhesion.

  16. Excitation and charge transfer in low-energy hydrogen atom collisions with neutral atoms: Theory, comparisons, and application to Ca

    CERN Document Server

    Barklem, Paul S

    2016-01-01

    A theoretical method for the estimation of cross sections and rates for excitation and charge transfer processes in low-energy hydrogen atom collisions with neutral atoms, based on an asymptotic two-electron model of ionic-covalent interactions in the neutral atom-hydrogen atom system, is presented. The calculation of potentials and non-adiabatic radial couplings using the method is demonstrated. The potentials are used together with the multi-channel Landau-Zener model to calculate cross sections and rate coefficients. The main feature of the method is that it employs asymptotically exact atomic wavefunctions, which can be determined from known atomic parameters. The method is applied to Li+H, Na+H, and Mg+H collisions, and the results compare well with existing detailed full-quantum calculations. The method is applied to the astrophysically important problem of Ca+H collisions, and rate coefficients are calculated for temperatures in the range 1000-20000 K.

  17. Dramatic effect of pore size reduction on the dynamics of hydrogen adsorbed in metal–organic materials

    KAUST Repository

    Nugent, Patrick

    2014-07-21

    The effects of pore size reduction on the dynamics of hydrogen sorption in metal-organic materials (MOMs) were elucidated by studying SIFSIX-2-Cu and its doubly interpenetrated polymorph SIFSIX-2-Cu-i by means of sorption, inelastic neutron scattering (INS), and computational modeling. SIFSIX-2-Cu-i exhibits much smaller pore sizes, which possess high H2 sorption affinity at low loadings. Experimental H2 sorption measurements revealed that the isosteric heat of adsorption (Qst) for H2 in SIFSIX-2-Cu-i is nearly two times higher than that for SIFSIX-2-Cu (8.6 vs. 4.6 kJ mol-1). The INS spectrum for H2 in SIFSIX-2-Cu-i is rather unique for a porous material, as only one broad peak appears at low energies near 6 meV, which simply increases in intensity with loading until the pores are filled. The value for this rotational transition is lower than that in most neutral metal-organic frameworks (MOFs), including those with open Cu sites (8-9 meV), which is indicative of a higher barrier to rotation and stronger interaction in the channels of SIFSIX-2-Cu-i than the open Cu sites in MOFs. Simulations of H2 sorption in SIFSIX-2-Cu-i revealed two hydrogen sorption sites in the MOM: direct interaction with the equatorial fluorine atom (site 1) and between two equatorial fluorine atoms on opposite walls (site 2). The calculated rotational energy levels and rotational barriers for the two sites in SIFSIX-2-Cu-i are in good agreement with INS data. Furthermore, the rotational barriers and binding energies for site 2 are slightly higher than that for site 1, which is consistent with INS results. The lowest calculated transition for the primary site in SIFSIX-2-Cu is also in good agreement with INS data. In addition, this transition in the non-interpenetrating material is higher than any of the sites in SIFSIX-2-Cu-i, which indicates a significantly weaker interaction with the host as a result of the larger pore size. This journal is © the Partner Organisations 2014.

  18. Structural, electronic and magnetic properties of 3d transition metal atom adsorbed germanene: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Pang, Qing, E-mail: pangqingjkd@163.com [College of Science, Xi' an University of Architecture and Technology, Xi' an 710055, Shaanxi (China); Li, Long; Zhang, Chun-Ling [College of Science, Xi' an University of Architecture and Technology, Xi' an 710055, Shaanxi (China); Wei, Xiu-Mei [College of Physics and Information Technology, Shaanxi Normal University, Xi' an 710062, Shaanxi (China); Song, Yu-Ling [College of Physics and Electronic Engineering, Nanyang Normal University, Nanyang 473061, Henan (China)

    2015-06-15

    The structural, electronic and magnetic properties of germanene adsorbed with 10 different 3d transition metal (TM) atoms have been investigated by using the spin-polarized DFT calculations. The 3d TM adatoms we considered prefer to bind to the hexagon hollow site of germanene, except Zn which favors to bind to the valley site. A strong covalent bonding character between TM adatom and germanene layer is found in most of TM/germanene adsorption systems. By means of adsorption, the germanene can exhibit various electronic and magnetic properties depending on the adatom species, such as nonmagnetic metal (Cu adsorption), nonmagnetic semiconductor (Ni or Zn adsorption), ferromagnetic metal (Cr or Mn adsorption), ferromagnetic semiconductor (V adsorption), and more particular, ferromagnetic half-metal (Sc, Ti, Fe or Co adsorption) with 100% spin-polarization at the Fermi level. In addition, Cr adatom introduces the largest magnetic moment in germanene, while Sc, Ti, V, Mn, Fe and Co adatoms all generate nearly integer magnetic moments. The effects of the on-site Coulomb interaction as well as the magnetic interaction between TM adatoms on the stability of the half-metallic TM/germanene systems are also considered, and the results show that the half-metallic states for the Sc/germanene and Ti/germanene are all robust. These ferromagnetic TM/germanene systems should have potential applications in the fields of two-dimensional spintronics devices. The analysis of the PDOS indicates the ferromagnetic property of the obtained TM/germanene systems mainly resulted from the spin-split of the TM 3d states. - Highlights: • Most of the 3d TM adatoms considered prefer to bind to the hexagon hollow site of germanene. • Strong covalent bonding between adatom and germanene is found in most of TM/germanene systems. • Germanene exhibits various electronic and magnetic properties depending on the adatom species. • The ferromagnetic property of TM/germanene systems mainly

  19. Centaurus A : Morphology and kinematics of the atomic hydrogen

    NARCIS (Netherlands)

    Struve, C.; Oosterloo, T. A.; Morganti, R.; Saripalli, L.

    2010-01-01

    We present new ATCA 21-cm line observations of the neutral hydrogen in the nearby radio galaxy Centaurus A. We image in detail (with a resolution down to 7 '', similar to 100 pc) the distribution of HI along the dust lane. Our data have better velocity resolution and better sensitivity than previous

  20. Adsorptive Removal of Pharmaceuticals and Personal Care Products from Water with Functionalized Metal-organic Frameworks: Remarkable Adsorbents with Hydrogen-bonding Abilities

    Science.gov (United States)

    Seo, Pill Won; Bhadra, Biswa Nath; Ahmed, Imteaz; Khan, Nazmul Abedin; Jhung, Sung Hwa

    2016-01-01

    Adsorption of typical pharmaceuticals and personal care products (PPCPs) (such as naproxen, ibuprofen and oxybenzone) from aqueous solutions was studied by using the highly porous metal-organic framework (MOF) MIL-101 with and without functionalization. Adsorption results showed that MIL-101s with H-donor functional groups such as –OH and –NH2 were very effective for naproxen adsorption, despite a decrease in porosity, probably because of H-bonding between O atoms on naproxen and H atoms on the adsorbent. For this reason, MIL-101 with two functional groups capable of H-bonding (MIL-101-(OH)2) exhibited remarkable adsorption capacity based on adsorbent surface area. The favorable contributions of –OH and –(OH)2 on MIL-101 in the increased adsorption of ibuprofen and oxybenzone (especially based on porosity) confirmed again the importance of H-bonding mechanism. The adsorbent with the highest adsorption capacity, MIL-101-OH, was very competitive when compared with carbonaceous materials, mesoporous materials, and pristine MIL-101. Moreover, the MIL-101-OH could be recycled several times by simply washing with ethanol, suggesting potential application in the adsorptive removal of PPCPs from water. PMID:27695005

  1. Hydrogen atom wave function and eigen energy in the Rindler space

    CERN Document Server

    Dai, De-Chang

    2016-01-01

    We study the hydrogen atom eigenstate energy and wave function in the Rindler space. The probability distribution is tilted because the electric field of the nucleus is no longer spherically symmetric. The hydrogen atom therefore cannot be treated exactly in the same way as what it is in an inertial frame. We also find that if the external force accelerates only the nucleus and then the nucleus accelerates its surrounding electrons through electromagnetic force, the electrons can tunnel through the local energy gap and split the hydrogen atom into an ion. This is similar to what one expects from the Stark effect. However, the critical acceleration is about $3\\times 10^{22} m/s^2$. It is well beyond the gravitational acceleration on a regular star surface.

  2. Fate of Accidental Symmetries of the Relativistic Hydrogen Atom in a Spherical Cavity

    CERN Document Server

    Al-Hashimi, M H; Wiese, U -J

    2015-01-01

    The non-relativistic hydrogen atom enjoys an accidental $SO(4)$ symmetry, that enlarges the rotational $SO(3)$ symmetry, by extending the angular momentum algebra with the Runge-Lenz vector. In the relativistic hydrogen atom the accidental symmetry is partially lifted. Due to the Johnson-Lippmann operator, which commutes with the Dirac Hamiltonian, some degeneracy remains. When the non-relativistic hydrogen atom is put in a spherical cavity of radius $R$ with perfectly reflecting Robin boundary conditions, characterized by a self-adjoint extension parameter $\\gamma$, in general the accidental $SO(4)$ symmetry is lifted. However, for $R = (l+1)(l+2) a$ (where $a$ is the Bohr radius and $l$ is the orbital angular momentum) some degeneracy remains when $\\gamma = \\infty$ or $\\gamma = \\frac{2}{R}$. In the relativistic case, we consider the most general spherically and parity invariant boundary condition, which is characterized by a self-adjoint extension parameter. In this case, the remnant accidental symmetry is ...

  3. Hydrogen atom wave function and eigen energy in the Rindler space

    Science.gov (United States)

    Dai, De-Chang

    2016-10-01

    We study the hydrogen atom eigenstate energy and wave function in the Rindler space. The probability distribution is tilted because the electric field of the nucleus is no longer spherically symmetric. The hydrogen atom therefore cannot be treated exactly in the same way as what it is in an inertial frame. We also find that if the external force accelerates only the nucleus and then the nucleus accelerates its surrounding electrons through electromagnetic force, the electrons can tunnel through the local energy gap and split the hydrogen atom into an ion. This is similar to what one expects from the Stark effect. However, the critical acceleration is about 3 ×1022 m /s2. It is well beyond the gravitational acceleration on a regular star surface.

  4. Lewis acid-water/alcohol complexes as hydrogen atom donors in radical reactions.

    Science.gov (United States)

    Povie, Guillaume; Renaud, Philippe

    2013-01-01

    Water or low molecular weight alcohols are, due to their availability, low price and low toxicity ideal reagents for organic synthesis. Recently, it was reported that, despite the very strong BDE of the O-H bond, they can be used as hydrogen atom donors in place of expensive and/or toxic group 14 metal hydrides when boron and titanium(III) Lewis acids are present. This finding represents a considerable innovation and uncovers a new perspective on the paradigm of hydrogen atom transfers to radicals. We discuss here the influence of complex formation and other association processes on the efficacy of the hydrogen transfer step. A delicate balance between activation by complex formation and deactivation by further hydrogen bonding is operative.

  5. Excitation and ionization of atomic hydrogen from various states

    NARCIS (Netherlands)

    Vriens, L.

    1965-01-01

    For large energies E1 of the impinging electrons, the cross sections Q for optically allowed excitation and ionization of atoms are given by Q = A/E1 ln cE1, where A and c are constants for one transition. For excitation A is proportional to the optical oscillator strength for the transition. For io

  6. Desulfurization of chalcopyrite and molybdenite by atomic hydrogen

    International Nuclear Information System (INIS)

    Molybdenite (MoS2) desulfurization by monatomic hydrogen in 625-800 K range was studied using helium as diluent gas. Desulfurization degree at 680 K equals 9%. Temperature growth elevates sulfur content in molybdenite. The effect of initial molybdenite enrichment with temperature growth up to 800 K is probably caused by removal of reduced molybdenum capable to form oxide in the presence of traces of oxygen contained in inert diluent gas

  7. Density-functional theory with screened van der Waals interactions applied to atomic and molecular adsorbates on close-packed and non-close-packed surfaces

    Science.gov (United States)

    Ruiz, Victor G.; Liu, Wei; Tkatchenko, Alexandre

    2016-01-01

    Modeling the adsorption of atoms and molecules on surfaces requires efficient electronic-structure methods that are able to capture both covalent and noncovalent interactions in a reliable manner. In order to tackle this problem, we have developed a method within density-functional theory (DFT) to model screened van der Waals interactions (vdW) for atoms and molecules on surfaces (the so-called DFT+vdWsurf method). The relatively high accuracy of the DFT+vdWsurf method in the calculation of both adsorption distances and energies, as well as the high degree of its reliability across a wide range of adsorbates, indicates the importance of the collective electronic effects within the extended substrate for the calculation of the vdW energy tail. We examine in detail the theoretical background of the method and assess its performance for adsorption phenomena including the physisorption of Xe on selected close-packed transition metal surfaces and 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on Au(111). We also address the performance of DFT+vdWsurf in the case of non-close-packed surfaces by studying the adsorption of Xe on Cu(110) and the interfaces formed by the adsorption of a PTCDA monolayer on the Ag(111), Ag(100), and Ag(110) surfaces. We conclude by discussing outstanding challenges in the modeling of vdW interactions for studying atomic and molecular adsorbates on inorganic substrates.

  8. Deformylation Reaction by a Nonheme Manganese(III)-Peroxo Complex via Initial Hydrogen-Atom Abstraction.

    Science.gov (United States)

    Barman, Prasenjit; Upadhyay, Pranav; Faponle, Abayomi S; Kumar, Jitendra; Nag, Sayanta Sekhar; Kumar, Devesh; Sastri, Chivukula V; de Visser, Sam P

    2016-09-01

    Metal-peroxo intermediates are key species in the catalytic cycles of nonheme metalloenzymes, but their chemical properties and reactivity patterns are still poorly understood. The synthesis and characterization of a manganese(III)-peroxo complex with a pentadentate bispidine ligand system and its reactivity with aldehydes was studied. Manganese(III)-peroxo can react through hydrogen-atom abstraction reactions instead of the commonly proposed nucleophilic addition reaction. Evidence of the mechanism comes from experiments which identify a primary kinetic isotope effect of 5.4 for the deformylation reaction. Computational modeling supports the established mechanism and identifies the origin of the reactivity preference of hydrogen-atom abstraction over nucleophilic addition.

  9. Exact semi-relativistic model for ionization of atomic hydrogen by electron impact

    OpenAIRE

    Attaourti, Y.; Taj, S.; Manaut, B.

    2004-01-01

    We present a semi-relativistic model for the description of the ionization process of atomic hydrogen by electron impact in the first Born approximation by using the Darwin wave function to describe the bound state of atomic hydrogen and the Sommerfeld-Maue wave function to describe the ejected electron. This model, accurate to first order in $Z/c$ in the relativistic correction, shows that, even at low kinetic energies of the incident electron, spin effects are small but not negligible. Thes...

  10. Reduction of uranium hexafluoride to tetrafluoride by using the hydrogen atoms

    Science.gov (United States)

    Aleksandrov, B. P.; Gordon, E. B.; Ivanov, A. V.; Kotov, A. A.; Smirnov, V. E.

    2016-09-01

    We consider the reduction of UF6 to UF4 by chemical reaction with hydrogen atoms originated in the powerful chemical generator. The principal design of such a chemical convertor is described. The results of the mathematical modeling of the thermodynamics and kinetics of the UF6 to UF4 reduction process are analyzed. The few options for the hydrogen atom generator design are proposed. A layout of the experimental setup with the chemical reactor is presented. The high efficiency together with the ability of the process scaling without loss of its efficiency makes this approach to the uranium hexafluoride depletion into tetrafluoride promising for its application in the industry.

  11. Band structure and decay channels of thorium-229 low-lying isomeric state for ensemble of thorium atoms adsorbed on calcium fluoride

    International Nuclear Information System (INIS)

    The results are presented on the study of the electronic structure of thorium atoms adsorbed by the liquid atomic layer deposition from aqueous solution of thorium nitrate on the surface of CaF2. The chemical state of the atoms and the change of the band structure in the surface layers of Th/CaF2 system on CaF2 substrate were investigated by XPS and REELS techniques. It was found that REELS spectra for Th/CaF2 system include peaks in the region of low energy losses (3-7 eV) which are missing in the similar spectra for pure CaF2. It is concluded that the presence of the observed features in the REELS spectra is associated with the chemical state of thorium atoms and is caused by the presence of uncompensated chemical bonds at the Th/CaF2 interface, and, therefore, by the presence of unbound 6d- and 7s-electrons of thorium atoms. Assuming the equivalence of the electronic configuration of thorium-229 and thorium-232 atoms, an estimate was made on the time decay of the excited state of thorium-229 nuclei through the channel of the electron conversion. It was found that the relaxation time is about 40 μs for 6d-electrons, and about 1 μs for 7s-electrons. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. Stability of the hydrogen atom of classical electrodynamics

    CERN Document Server

    De Luca, J

    2004-01-01

    We study the stability of the circular orbits of the electromagnetic two-body problem of classical electrodynamics. We introduce the concept of resonant dissipation, i.e. a motion that radiates the center-of-mass energy while the interparticle distance performs bounded oscillations about a metastable orbit. The stability mechanism is established by the existence of a quartic resonant constant generated by the stiff eigenvalues of the linear stability problem. This constant bounds the particles together during the radiative recoil. The condition of resonant dissipation predicts angular momenta for the metastable orbits in reasonable agreement with the Bohr atom. The principal result is that the emission lines agree with the predictions of quantum electrodynamics (QED) with 1 percent average error even up to the $40^{th}$ line. Our angular momenta depend logarithmically on the mass of the heavy body, such that the deuterium and the muonium atoms have essentially the same angular momenta, in agreement with QED. ...

  13. Do Spin State and Spin Density Affect Hydrogen Atom Transfer Reactivity?

    OpenAIRE

    Saouma, Caroline T.; Mayer, James M.

    2013-01-01

    The prevalence of hydrogen atom transfer (HAT) reactions in chemical and biological systems has prompted much interest in establishing and understanding the underlying factors that enable this reactivity. Arguments have been advanced that the electronic spin state of the abstractor and/or the spin-density at the abstracting atom are critical for HAT reactivity. This is consistent with the intuition derived from introductory organic chemistry courses. Herein we present an alternative view on t...

  14. Laser-induced reaction of Yb atoms with hydrogen chloride in the gas phase

    International Nuclear Information System (INIS)

    The results are presented of an investigation of the reaction of ytterbium atoms with hydrogen chloride initiated by laser radiation resonant with the 1S/sub O/-3P1 intercombination transition. The rate constant of extinction of the excited state of the ytterbium atom by a molecular reagent was measured: k/sub d/ = (6.4 +- 1.5) x 10-10 cm3sec

  15. Hydrogen-Atom Attack on Methyl Viologen in Aqueous Solution Studied by Pulse Radiolysis

    DEFF Research Database (Denmark)

    Solar, S.; Solar, W.; Getoff, N.;

    1984-01-01

    Using hydrogen at high pressures of up to 150 bar (0.12 mol dm–3 H2) as an OH scavenger in aqueous MV2+ solutions (pH 1) it is possible to differentiate between two kinds of transient formed simultaneously by H-atom attack on methyl viologen. One of them is assigned to an H adduct on the N atom, ......–7); its absorption spectrum does not change in this pH range....

  16. Ionization of hydrogen atom by X-ray absorption in the presence of optical laser field

    International Nuclear Information System (INIS)

    The absorption of X-rays in hydrogen atom considering the irradiation of the target by an intense optical laser of frequency ω is studied. It is found that the terms of the modified scattering amplitude has different dependence on polarization vectors of X-ray fields and laser fields. There is resonance in the differential cross section for absorption at different frequencies when ω (the laser frequency) becomes nearly equal to atomic transition frequency. (author). 21 refs., 2 figs

  17. Sensitive detection of fast, neutral hydrogen atoms for the Bound Beta-Decay (BoB) experiment

    International Nuclear Information System (INIS)

    We are currently exploring methods to detect hydrogen atoms with 325.7 eV kinetic energy. These atoms form the decay signature of the theoretically-predicted three-body decay of the neutron into a hydrogen atom and an anti-neutrino. The challenge in designing and building such a hydrogen detector lies in the small predicted branching ratio for this decay (10-6 of the three-body decay), the low energy of the atoms and the requirement to identify them over background hydrogen. This talk describes our preliminary work investigating three possible detection schemes: quenching of H(2s) atoms and subsequent detection of the resulting Lyman-α photon, charge-exchange of hydrogen atoms in argon gas and laser ionisation.

  18. Linear quadratic stochastic control of atomic hydrogen masers.

    Science.gov (United States)

    Koppang, P; Leland, R

    1999-01-01

    Data are given showing the results of using the linear quadratic Gaussian (LQG) technique to steer remote hydrogen masers to Coordinated Universal Time (UTC) as given by the United States Naval Observatory (USNO) via two-way satellite time transfer and the Global Positioning System (GPS). Data also are shown from the results of steering a hydrogen maser to the real-time USNO mean. A general overview of the theory behind the LQG technique also is given. The LQG control is a technique that uses Kalman filtering to estimate time and frequency errors used as input into a control calculation. A discrete frequency steer is calculated by minimizing a quadratic cost function that is dependent on both the time and frequency errors and the control effort. Different penalties, chosen by the designer, are assessed by the controller as the time and frequency errors and control effort vary from zero. With this feature, controllers can be designed to force the time and frequency differences between two standards to zero, either more or less aggressively depending on the application. PMID:18238452

  19. Use of Ni/NixB Nanoparticles as a Novel Adsorbent for the Preconcentration of Mercury Species prior to Cold Vapor-Atomic Fluorescence Spectrometric Determination.

    Science.gov (United States)

    Yayayürük, Onur; Henden, Emür

    2016-01-01

    A selective matrix separation/enrichment method, utilizing a simple batch procedure with nickel/nickel boride (Ni/NixB) nanoparticles was proposed for the determination of inorganic mercury(II), Hg(2+) and methyl mercury(I), CH3Hg(+) in waters prior to cold vapor-atomic fluorescence spectrometry (CV-AFS). The Ni/NixB nanoparticles, were synthesized by the chemical reduction of Ni(II) to Ni/NixB. The novel adsorbent was selective to Hg(2+) and CH3Hg(+) species between pH values of 4 - 10. Both of the mercury species were recovered from the adsorbent using 1.0 mol L(-1) hot HNO3 with high efficiency. It was observed that the adsorbent selectively removed Hg(2+) and CH3Hg(+) from the bulk solution in the presence of several competitor ions (As(3+), Sb(3+), Pb(2+), Zn(2+), Cu(2+), Cd(2+) and Fe(3+)) with ≥96% adsorption. The limit of detection (3σ above blank) was found to be 1.8 ng L(-1) with a preconcentration factor of 20. The validation of the method was tested through spike recovery experiments with several water samples (tap and seawater) at μg L(-1) concentration levels, and all recovery values were found to vary between 95 and 105%. PMID:27506713

  20. Entanglement harvesting from the electromagnetic vacuum with hydrogen-like atoms

    CERN Document Server

    Pozas-Kerstjens, Alejandro

    2016-01-01

    We study how two fully-featured hydrogen-like atoms harvest entanglement from the electromagnetic field vacuum, even when the atoms are spacelike separated. We compare the electromagnetic case ---qualitatively and quantitatively--- with previous results that used scalar fields and featureless, idealized atomic models. Our study reveals the new traits that emerge when we relax these idealizations, such as anisotropies in entanglement harvesting and the effect of exchange of angular momentum. We show that, under certain circumstances, relaxing previous idealizations makes vacuum entanglement harvesting more efficient.

  1. Interference Dynamics of Hydrogen Atoms in High-Frequency Dichromatic Laser Fields

    Institute of Scientific and Technical Information of China (English)

    程太旺; 李晓峰; 傅盘铭; 陈式刚

    2002-01-01

    We investigate the ionization and high-order harmonic generation of a hydrogen atom in high-frequency (several atomic units) super strong (up to several tens of atomic units) dichromatic laser fields. An effective iterative method in the framework of high-frequency Floquet theory is used in the calculations. We have considered two kinds of dichromatic laser field, i.e. 1ω - 2ω and lω - 3ω. We find that, in both the cases, the ionization and high-order harmonic generation show evident dependence on the relative phase and strength of the additional harmonic field. The dynamical origin of these interference effects is also discussed.

  2. Diffusion radius of muonic hydrogen atoms in H-D gas

    OpenAIRE

    Adamczak, Andrzej; Gronowski, Jakub

    2006-01-01

    The diffusion radius of the 1S muonic hydrogen atoms in gaseous H_2 targets with various deuterium admixtures has been determined for temperatures T=30 and 300 K. The Monte Carlo calculations have been performed using the partial differential crosssections for $p\\mu$ and $d\\mu$ atom scattering from the molecules H$_2$, HD and D$_2$. These cross sections include hyperfine transitions in the muonic atoms, the muon exchange between the nuclei $p$ and $d$, and rotational-vibrational transitions i...

  3. Time-resolved ionization of the hydrogen atom in strong laser fields

    International Nuclear Information System (INIS)

    We use the strong field approximation to study the single-photon ionization of the hydrogen atom in the time domain. During the interaction of the laser pulse and the atom, the electron is pumped to the Volkov state and has a widely energy distribution at the beginning of the laser pulse. With the time evolution, only the photon-electron with the energy hra - Ip is survived, where to is the laser angular frequency, and Ip is the ionization potential of the atom. Therefore we observed how the energy spectrum of the ionized electron builds in the time domain.

  4. Solving problems on hydrogen atom in electric field by means of REDUCE

    International Nuclear Information System (INIS)

    A technique of solving perturbation theory problems of quantum mechanics in the language of the dynamic symmetry group by means of REDUCE computer algebra system is discussed. The program for analytical calculation of energy and wave functions of hydrogen atom in an electric field in arbitrary order of the perturbation theory is presented

  5. Angular correlation measurements for the 32Dsub(j) states of atomic hydrogen

    International Nuclear Information System (INIS)

    Angular correlation measurements have been made of the Lyman-α radiation arising from the cascade of the 32Dsub(j) states of atomic hydrogen detected in coincidence with electron scattered with n=3 energy loss. Data are presented at incident energies of 54.4 and 100 eV and electron scattering angles thetasub(e)=20 and 250. (author)

  6. Quantum dynamics of hydrogen atoms on graphene. I. System-bath modeling

    International Nuclear Information System (INIS)

    An accurate system-bath model to investigate the quantum dynamics of hydrogen atoms chemisorbed on graphene is presented. The system comprises a hydrogen atom and the carbon atom from graphene that forms the covalent bond, and it is described by a previously developed 4D potential energy surface based on density functional theory ab initio data. The bath describes the rest of the carbon lattice and is obtained from an empirical force field through inversion of a classical equilibrium correlation function describing the hydrogen motion. By construction, model building easily accommodates improvements coming from the use of higher level electronic structure theory for the system. Further, it is well suited to a determination of the system-environment coupling by means of ab initio molecular dynamics. This paper details the system-bath modeling and shows its application to the quantum dynamics of vibrational relaxation of a chemisorbed hydrogen atom, which is here investigated at T = 0 K with the help of the multi-configuration time-dependent Hartree method. Paper II deals with the sticking dynamics

  7. Multigrid solution of a path integral formulation for the hydrogen atom

    CERN Document Server

    Bai, D

    2004-01-01

    An efficient multigrid Monte-Carlo algorithm for calculating the ground state of the hydrogen atom using path integral is presented. The algorithm uses a unigrid approach. The action integral near r=0 is modified so that the correct values of observables are obtained. It is demonstrated that the critical slow down (CSD) is eliminated. Finally, the algorithm is compared to the staging algorithm.

  8. Existence of a ground state for the confined hydrogen atom in non-relativistic QED

    DEFF Research Database (Denmark)

    Amour, Laurent; Faupin, Jeremy

    2008-01-01

    We consider a system of a hydrogen atom interacting with the quantized electromagnetic field. Instead of fixing the nucleus, we assume that the system is confined by its center of mass. This model is used in theoretical physics to explain the Lamb-Dicke effect. After a brief review of the...

  9. Continuous vs. discrete models for the quantum harmonic oscillator and the hydrogen atom

    CERN Document Server

    Lorente, M

    2001-01-01

    The Kravchuk and Meixner polynomials of discrete variable are introduced for the discrete models of the harmonic oscillator and hydrogen atom. Starting from Rodrigues formula we construct raising and lowering operators, commutation and anticommutation relations. The physical properties of discrete models are figured out through the equivalence with the continuous models obtained by limit process.

  10. Continuous vs. discrete models for the quantum harmonic oscillator and the hydrogen atom

    OpenAIRE

    Lorente, M

    2004-01-01

    The Kravchuk and Meixner polynomials of discrete variable are introduced for the discrete models of the harmonic oscillator and hydrogen atom. Starting from Rodrigues formula we construct raising and lowering operators, commutation and anticommutation relations. The physical properties of discrete models are figured out through the equivalence with the continuous models obtained by limit process.

  11. Continuous vs. discrete models for the quantum harmonic oscillator and the hydrogen atom

    Science.gov (United States)

    Lorente, Miguel

    2001-07-01

    The Kravchuk and Meixner polynomials of discrete variable are introduced for the discrete models of the harmonic oscillator and hydrogen atom. Starting from Rodrigues formula we construct raising and lowering operators, commutation and anticommutation relations. The physical properties of discrete models are figured out through the equivalence with the continuous models obtained by limit process.

  12. Effect of vacuum polarization on the excitation of hydrogen atom by electron impact

    Directory of Open Access Journals (Sweden)

    Sujata Bhattacharyya

    1981-01-01

    for 1S−2S excitation of the hydrogen atom by electron impact. The excitation amplitude calculated field theoretically is found to be lowered by 0.47t2/(t2+93 where t2=4|P−Q|2, P and Q being the momenta of the incident and scattered electrons respectively.

  13. Quantum dynamics of hydrogen atoms on graphene. I. System-bath modeling

    Energy Technology Data Exchange (ETDEWEB)

    Bonfanti, Matteo, E-mail: matteo.bonfanti@unimi.it [Dipartimento di Chimica, Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Jackson, Bret [Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003 (United States); Hughes, Keith H. [School of Chemistry, Bangor University, Bangor, Gwynedd LL57 2UW (United Kingdom); Burghardt, Irene [Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main (Germany); Martinazzo, Rocco, E-mail: rocco.martinazzo@unimi.it [Dipartimento di Chimica, Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Istituto di Scienze e Tecnologie Molecolari, Consiglio Nazionale delle Richerche, v. Golgi 19, 20133 Milano (Italy)

    2015-09-28

    An accurate system-bath model to investigate the quantum dynamics of hydrogen atoms chemisorbed on graphene is presented. The system comprises a hydrogen atom and the carbon atom from graphene that forms the covalent bond, and it is described by a previously developed 4D potential energy surface based on density functional theory ab initio data. The bath describes the rest of the carbon lattice and is obtained from an empirical force field through inversion of a classical equilibrium correlation function describing the hydrogen motion. By construction, model building easily accommodates improvements coming from the use of higher level electronic structure theory for the system. Further, it is well suited to a determination of the system-environment coupling by means of ab initio molecular dynamics. This paper details the system-bath modeling and shows its application to the quantum dynamics of vibrational relaxation of a chemisorbed hydrogen atom, which is here investigated at T = 0 K with the help of the multi-configuration time-dependent Hartree method. Paper II deals with the sticking dynamics.

  14. CALCULATED PROPERTIES OF TWO-DIMENSIONAL SPIN-POLARIZED ATOMIC HYDROGEN

    OpenAIRE

    Lantto, L.; Nieminen, R.

    1980-01-01

    Optimal HNC-Jastrow calculations have been carried out for gaseous spin-polarized hydrogen in two space dimensions. Accurate values for the ground state energy, radial distribution function, average exchange energy and momentum distribution are obtained at low atomic densities.

  15. Effects of laser radiation field on energies of hydrogen atom in plasmas

    International Nuclear Information System (INIS)

    In this study, for the first time, the Schrödinger equation with more general exponential cosine screened Coulomb (MGECSC) potential is solved numerically in the presence of laser radiation field within the Ehlotzky approximation using the asymptotic iteration method. The MGECSC potential includes four different potential forms in consideration of different sets of the parameters in the potential. By applying laser field, the total interaction potential of hydrogen atom embedded in plasmas converts to double well-type potential. The plasma screening effects under the influence of laser field as well as confinement effects of laser field on hydrogen atom in Debye and quantum plasmas are investigated by solving the Schrödinger equation with the laser-dressed MGECSC potential. It is resulted that since applying a monochromatic laser field on hydrogen atom embedded in a Debye and quantum plasma causes to shift in the profile of the total interaction potential, the confinement effects of laser field on hydrogen atom in plasmas modeled by the MGECSC potential change localizations of energy states

  16. Pregalactic black hole formation with an atomic hydrogen equation of state

    NARCIS (Netherlands)

    Spaans, Marco; Silk, Joseph

    2006-01-01

    The polytropic equation of state of an atomic hydrogen gas is examined for primordial halos with baryonic masses of M-h similar to 10(7)-10(9) M-circle dot. For roughly isothermal collapse around 10(4) K, we find that line trapping of Ly alpha (H I and He II) photons causes the polytropic exponent t

  17. Learning about Regiochemistry from a Hydrogen-Atom Abstraction Reaction in Water

    Science.gov (United States)

    Sears-Dundes, Christopher; Huon, Yoeup; Hotz, Richard P.; Pinhas, Allan R.

    2011-01-01

    An experiment has been developed in which the hydrogen-atom abstraction and the coupling of propionitrile, using Fenton's reagent, are investigated. Students learn about the regiochemistry of radical formation, the stereochemistry of product formation, and the interpretation of GC-MS data, in a safe reaction that can be easily completed in one…

  18. Hot hydrogen atoms in a water-vapor microwave plasma source

    Energy Technology Data Exchange (ETDEWEB)

    Tatarova, E.; Dias, F.M.; Ferreira, C.M. [Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal)

    2009-12-15

    A study of the hydrogen Balmer line shape in a water-vapor, microwave slot-antenna excited plasma source operated at 2.45 GHz is reported. The emission profiles of the H{sub {alpha}} and H{sub {beta}} lines are well fitted by Gaussian profiles. Excited hydrogen atoms are detected in the remote plasma zone of the source up to 30 cm distance from the exciting antennas. The measured Doppler temperature corresponding to the H{sub {beta}} line broadening is about three times higher than the rotational temperature of the hydrogen molecular Fulcher-{alpha} band. It has been found clear evidence for the existence of a local source of excited ''hot'' hydrogen atoms in the ''microwave field free'' remote plasma zone. The measured Doppler broadening of the O(777.4 nm) triplet line indicates that ''hot'' oxygen atoms, with an energy around 0.3 eV, are also created in this source. Exothermic electron-ion and ion-ion recombination processes as well as DC distributed potentials existing in inhomogeneous remote plasma are possible local sources of ''hot'' atoms in the far remote plasma zone. (author)

  19. On the proton exchange contribution to electron-hydrogen atom elastic scattering

    International Nuclear Information System (INIS)

    It is shown that the exchange contribution to the electron-proton potential Born term in elastic electron-hydrogen atom scattering arises as the non relativistic limit from the exchange of a proton between the two participant electrons - calculated from quantum electrodynamics including properly bound states (as solution of Bethe - Salpeter equation). (Author)

  20. Hydrogen atom ionization by fast electrons in an external electric field

    International Nuclear Information System (INIS)

    Hydrogen atom ionization by fast electrons in an external electric field is considered. The oscillative character of ionization is referred to interference effects, occuring under electron transition to states of continuous energy spectrum. These states are described by wave functions in the form of standing waves

  1. SPIRAL STRUCTURE OF M51 - DISTRIBUTION AND KINEMATICS OF THE ATOMIC AND IONIZED HYDROGEN

    NARCIS (Netherlands)

    TILANUS, RPJ; ALLEN, RJ

    1991-01-01

    The atomic hydrogen (H I) and the H-alpha emission lines in the grand-design spiral galaxy M51 have been observed with the Westerbork Synthesis Radio Telescope and the TAURUS Fabry-Perot imaging spectrometer, respectively. Across the inner spiral arms significant tangential and radial velocity gradi

  2. Determination of the Relative Atomic Masses of Metals by Liberation of Molecular Hydrogen

    Science.gov (United States)

    Waghorne, W. Earle; Rous, Andrew J.

    2009-01-01

    Students determine the relative atomic masses of calcium, magnesium, and aluminum by reaction with hydrochloric acid and measurement of the volume of hydrogen gas liberated. The experiment demonstrates stoichiometry and illustrates clearly that mass of the reagent is not the determinant of the amounts in chemical reactions. The experiment is…

  3. Four kinds of raising and lowering operators of n-dimensional hydrogen atom and isotropic harmonic oscillator

    Institute of Scientific and Technical Information of China (English)

    刘宇峰; 曾谨言

    1997-01-01

    The factorization of the radial Schrodinger equation of n-dimensional (n≥2) hydrogen atoms and isotropic harmonic oscillators was investigated and four kinds of raising and lowering operators were derived.The relation between n -dimensional (n≥2) and one-dimensional hydrogen atoms and harmonic oscillators was discussed.

  4. Construction of the isocopalane skeleton: application of a desulfinylative 1,7-hydrogen atom transfer strategy.

    Science.gov (United States)

    Xiao, Xiong; Xu, ZhongYu; Zeng, Qian-Ding; Chen, Xi-Bo; Ji, Wen-Hao; Han, Ying; Wu, PeiYing; Ren, Jiangmeng; Zeng, Bu-Bing

    2015-06-01

    Two attractive chirons, aldehyde 6 and chloride 7, exhibiting functionalized ent-spongiane-type tricyclic skeletons (ABC ring system), have been constructed and their absolute configurations have been studied by NMR spectroscopy and confirmed by single-crystal X-ray diffraction. Both of these chirons are derived from commercially available andrographolide in good yield. Aldehyde 6 is obtained through a novel K2 S2 O8 -catalyzed aquatic ring-closing reaction of allylic sodium sulfonate and intramolecular 1,7-hydrogen atom transfer process. Further mechanistic investigations demonstrate that the 1,7-hydrogen atom transfer is a free-radical process, whereby hydrogen migrates from C18 to C17, as evidenced by double-18- deuterium-labeled isotope experiments. Prospective applications of these two chiral sources are also discussed. PMID:25907201

  5. Spontaneous absorption of an accelerated hydrogen atom near a conducting plane in vacuum

    CERN Document Server

    Yu, H; Yu, Hongwei; Zhu, Zhiying

    2006-01-01

    We study, in the multipolar coupling scheme, a uniformly accelerated multilevel hydrogen atom in interaction with the quantum electromagnetic field near a conducting boundary and separately calculate the contributions of the vacuum fluctuation and radiation reaction to the rate of change of the mean atomic energy. It is found that the perfect balance between the contributions of vacuum fluctuations and radiation reaction that ensures the stability of ground-state atoms is disturbed, making spontaneous transition of ground-state atoms to excited states possible in vacuum with a conducting boundary. The boundary-induced contribution is effectively a nonthermal correction, which enhances or weakens the nonthermal effect already present in the unbounded case, thus possibly making the effect easier to observe. An interesting feature worth being noted is that the nonthermal corrections may vanish for atoms on some particular trajectories.

  6. Preconcentration of Co, Ni, Cd and Zn on naphthalene–2,4,6-trimorpholino-1,3,5-triazin adsorbent and flame atomic absorption determination

    Directory of Open Access Journals (Sweden)

    TAYYEBEH MADRAKIAN

    2010-05-01

    Full Text Available A preconcentration method was developed for the determination of trace amounts of Co, Ni, Cd and Zn by atomic absorption spectrometry. The method is based on the retention of the metal cations by naphthalene–2,4,6-trimorpholino-1,3,5-triazin adsorbent in a column. The adsorbed metals were then eluted from the column with hydrochloric acid and the Co, Ni, Cd and Zn were determined by flame atomic absorption spectrometry. The optimal extraction and elution conditions were studied. The effects of diverse ions on the preconcentration were also investigated. A preconcentration factor of 250 for Co(II, Ni(II and Zn(II, and 400 for Cd(II can easily be achieved. Calibration graphs were obtained and the detection limits of the method for Co(II, Ni(II, Cd(II and Zn(II were 0.51, 0.49, 0.17 and 0.10 ng mL-1, respectively. The relative standard deviations (RSD of 0.37–2.31 % for Co, 0.37–3.73 % for Ni, 2.20–2.40 % for Cd and 1.50–2.56 % for Zn were obtained. The method was also used for the simultaneous preconcentration of these elements and the method was successfully applied to their preconcentration and determination. The method was applied to the determination of Co, Ni, Cd and Zn in several real samples.

  7. Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

    Energy Technology Data Exchange (ETDEWEB)

    Lee, June Key, E-mail: junekey@jnu.ac.kr, E-mail: hskim7@jbnu.ac.kr; Hyeon, Gil Yong; Tawfik, Wael Z.; Choi, Hee Seok [Department of Materials Science and Engineering, and Optoelectronics Convergence Research Center, Chonnam National University, Gwangju 500-757 (Korea, Republic of); Ryu, Sang-Wan [Department of Physics and Optoelectronics Convergence Research Center, Chonnam National University, Gwangju 500-757 (Korea, Republic of); Jeong, Tak [Korea Photonics Technology Institute, Gwangju 500-460 (Korea, Republic of); Jung, Eunjin; Kim, Hyunsoo, E-mail: junekey@jnu.ac.kr, E-mail: hskim7@jbnu.ac.kr [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)

    2015-05-14

    Hydrogen atoms inside of an Mg-doped GaN epitaxial layer were effectively removed by the electrochemical potentiostatic activation (EPA) method. The role of hydrogen was investigated in terms of the device performance of light-emitting diodes (LEDs). The effect of the main process parameters for EPA such as solution type, voltage, and time was studied and optimized for application to LED fabrication. In optimized conditions, the light output of 385-nm LEDs was improved by about 26% at 30 mA, which was caused by the reduction of the hydrogen concentration by ∼35%. Further removal of hydrogen seems to be involved in the breaking of Ga-H bonds that passivate the nitrogen vacancies. An EPA process with high voltage breaks not only Mg-H bonds that generate hole carriers but also Ga-H bonds that generate electron carriers, thus causing compensation that impedes the practical increase of hole concentration, regardless of the drastic removal of hydrogen atoms. A decrease in hydrogen concentration affects the current-voltage characteristics, reducing the reverse current by about one order and altering the forward current behavior in the low voltage region.

  8. Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

    International Nuclear Information System (INIS)

    Hydrogen atoms inside of an Mg-doped GaN epitaxial layer were effectively removed by the electrochemical potentiostatic activation (EPA) method. The role of hydrogen was investigated in terms of the device performance of light-emitting diodes (LEDs). The effect of the main process parameters for EPA such as solution type, voltage, and time was studied and optimized for application to LED fabrication. In optimized conditions, the light output of 385-nm LEDs was improved by about 26% at 30 mA, which was caused by the reduction of the hydrogen concentration by ∼35%. Further removal of hydrogen seems to be involved in the breaking of Ga-H bonds that passivate the nitrogen vacancies. An EPA process with high voltage breaks not only Mg-H bonds that generate hole carriers but also Ga-H bonds that generate electron carriers, thus causing compensation that impedes the practical increase of hole concentration, regardless of the drastic removal of hydrogen atoms. A decrease in hydrogen concentration affects the current-voltage characteristics, reducing the reverse current by about one order and altering the forward current behavior in the low voltage region

  9. Stabilizing a Platinum1 Single-Atom Catalyst on Supported Phosphomolybdic Acid without Compromising Hydrogenation Activity.

    Science.gov (United States)

    Zhang, Bin; Asakura, Hiroyuki; Zhang, Jia; Zhang, Jiaguang; De, Sudipta; Yan, Ning

    2016-07-11

    In coordination chemistry, catalytically active metal complexes in a zero- or low-valent state often adopt four-coordinate square-planar or tetrahedral geometry. By applying this principle, we have developed a stable Pt1 single-atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)-modified active carbon. This was achieved by anchoring Pt on the four-fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square-planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities.

  10. Stabilizing a Platinum1 Single-Atom Catalyst on Supported Phosphomolybdic Acid without Compromising Hydrogenation Activity.

    Science.gov (United States)

    Zhang, Bin; Asakura, Hiroyuki; Zhang, Jia; Zhang, Jiaguang; De, Sudipta; Yan, Ning

    2016-07-11

    In coordination chemistry, catalytically active metal complexes in a zero- or low-valent state often adopt four-coordinate square-planar or tetrahedral geometry. By applying this principle, we have developed a stable Pt1 single-atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)-modified active carbon. This was achieved by anchoring Pt on the four-fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square-planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities. PMID:27240266

  11. Dephenolization of stored olive-mill wastewater, using four different adsorbing matrices to attain a low-cost feedstock for hydrogen photo-production.

    Science.gov (United States)

    Padovani, Giulia; Pintucci, Cristina; Carlozzi, Pietro

    2013-06-01

    This investigation deals with the conversion of olive-mill wastewater (OMW) into several feedstocks suitable for hydrogen photo-production. The goal was reached by means of two sequential steps: (i) a pre-treatment process of stored-OMW for the removal of polyphenols, which made it possible to obtain several effluents, and (ii) a photo-fermentative process for hydrogen production by means of Rhodopseudomonas palustris sp. Four different adsorbent matrices (Azolla, granular active carbon, resin, and zeolite) were used to dephenolize stored-OMW. The four liquid fractions attained by using the above process created the same number of effluents, and these were diluted with water and then used for hydrogen photo-production. The maximum hydrogen production rate (14.31 mL/L/h) was attained with the photo-fermenter containing 25% of the effluent, which came from the pre-treatment of stored-OMW using granular active carbon. Using the carbon effluent as feedstock, the greatest light conversion efficiency of 2.29% was achieved. PMID:23612177

  12. Single-Atom Pd₁/Graphene Catalyst Achieved by Atomic Layer Deposition: Remarkable Performance in Selective Hydrogenation of 1,3-Butadiene.

    Science.gov (United States)

    Yan, Huan; Cheng, Hao; Yi, Hong; Lin, Yue; Yao, Tao; Wang, Chunlei; Li, Junjie; Wei, Shiqiang; Lu, Junling

    2015-08-26

    We reported that atomically dispersed Pd on graphene can be fabricated using the atomic layer deposition technique. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy both confirmed that isolated Pd single atoms dominantly existed on the graphene support. In selective hydrogenation of 1,3-butadiene, the single-atom Pd1/graphene catalyst showed about 100% butenes selectivity at 95% conversion at a mild reaction condition of about 50 °C, which is likely due to the changes of 1,3-butadiene adsorption mode and enhanced steric effect on the isolated Pd atoms. More importantly, excellent durability against deactivation via either aggregation of metal atoms or carbonaceous deposits during a total 100 h of reaction time on stream was achieved. Therefore, the single-atom catalysts may open up more opportunities to optimize the activity, selectivity, and durability in selective hydrogenation reactions. PMID:26268551

  13. Band structure and decay channels of thorium-229 low-lying isomeric state for ensemble of thorium atoms adsorbed on calcium fluoride

    Energy Technology Data Exchange (ETDEWEB)

    Borisyuk, Petr V.; Vasilyev, Oleg S.; Krasavin, Andrey V.; Troyan, Victor I. [National Research Nuclear University ' ' MEPhI' ' (Moscow Engineering Physics Institute), Kashirskoye shosse 31, 115409 Moscow (Russian Federation); Lebedinskii, Yury Yu. [National Research Nuclear University ' ' MEPhI' ' (Moscow Engineering Physics Institute), Kashirskoye shosse 31, 115409 Moscow (Russian Federation); Moscow Institute of Physics and Technology (State University), Institutskiy per. 9, 141700 Dolgoprudny, Moscow region (Russian Federation); Tkalya, Eugene V. [Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Leninskie gory, 119991 Moscow (Russian Federation); Nuclear Safety Institute of Russian Academy of Science, Bol' shaya Tulskaya 52, 115191 Moscow (Russian Federation)

    2015-12-15

    The results are presented on the study of the electronic structure of thorium atoms adsorbed by the liquid atomic layer deposition from aqueous solution of thorium nitrate on the surface of CaF{sub 2}. The chemical state of the atoms and the change of the band structure in the surface layers of Th/CaF{sub 2} system on CaF{sub 2} substrate were investigated by XPS and REELS techniques. It was found that REELS spectra for Th/CaF{sub 2} system include peaks in the region of low energy losses (3-7 eV) which are missing in the similar spectra for pure CaF{sub 2}. It is concluded that the presence of the observed features in the REELS spectra is associated with the chemical state of thorium atoms and is caused by the presence of uncompensated chemical bonds at the Th/CaF{sub 2} interface, and, therefore, by the presence of unbound 6d- and 7s-electrons of thorium atoms. Assuming the equivalence of the electronic configuration of thorium-229 and thorium-232 atoms, an estimate was made on the time decay of the excited state of thorium-229 nuclei through the channel of the electron conversion. It was found that the relaxation time is about 40 μs for 6d-electrons, and about 1 μs for 7s-electrons. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Formation and Transport of Atomic Hydrogen in Hot-Filament Chemical Vapor Deposition Reactors

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant ishydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers forheat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phaseheat and mass transfer, respectively. A simplified model has been established to simulate gas-phase temperature andH concentration distributions between the filament and the substrate. Examination of the relative importance ofhomogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecularhydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociationrates of H2 for various filament temperatures were calculated to match H-atom concentrations observed in the liter-ature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociationrates suggest that dissociation of H2 at refractory filament surface is a catalytic process, which has a rather lowereffective activation energy than homogeneous thermal dissociation. Atomic hydrogen, acting as an important heattransfer medium to heat the substrate, can freely diffuse from the filament to the substrate without recombination.

  15. Nanochemistry at the atomic scale revealed in hydrogen-induced semiconductor surface metallization

    Science.gov (United States)

    Derycke, Vincent; Soukiassian, Patrick G.; Amy, Fabrice; Chabal, Yves J.; D'Angelo, Marie D.; Enriquez, Hanna B.; Silly, Mathieu G.

    2003-04-01

    Passivation of semiconductor surfaces against chemical attack can be achieved by terminating the surface-dangling bonds with a monovalent atom such as hydrogen. Such passivation invariably leads to the removal of all surface states in the bandgap, and thus to the termination of non-metallic surfaces. Here we report the first observation of semiconductor surface metallization induced by atomic hydrogen. This result, established by using photo-electron and photo-absorption spectroscopies and scanning tunnelling techniques, is achieved on a Si-terminated cubic silicon carbide (SiC) surface. It results from competition between hydrogen termination of surface-dangling bonds and hydrogen-generated steric hindrance below the surface. Understanding the ingredient for hydrogen-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides a means to develop electrical contacts on high-bandgap chemically passive materials, particularly for interfacing with biological systems, and gives control of surfaces for lubrication, for example of nanomechanical devices.

  16. Quantized magnetic flux through the orbits of hydrogen-like atoms

    Energy Technology Data Exchange (ETDEWEB)

    Stein, Wolf-Dieter R. [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin (Germany)

    2013-07-01

    I report on the investigation of the quantization of the magnetic flux through the orbits of the hydrogen atom on the basis of the Rutherford-Bohr model of the atom. In contrast to earlier studies based on magnetic fields originating from the magnetic moment of the proton, here the origin of the magnetic flux is taken to be the orbiting electron itself. The magnetic moment of the proton causes an additional magnetic flux through the atomic orbits resulting in small energy shifts of the atomic levels, which are studied in more detail. The energy difference due to opposite directions of the magnetic moment of the proton results in a fractional amount of 3/8 of the hyperfine level splitting of the lowest Bohr orbit. Such a ratio was also observed for the fine structure energy level splitting when the spin of the electron is neglected. Generalizations are discussed.

  17. Diffusion radius of muonic hydrogen atoms in H-D gas

    CERN Document Server

    Adamczak, A; Adamczak, Andrzej; Gronowski, Jakub

    2006-01-01

    The diffusion radius of the 1S muonic hydrogen atoms in gaseous H_2 targets with various deuterium admixtures has been determined for temperatures T=30 and 300 K. The Monte Carlo calculations have been performed using the partial differential crosssections for $p\\mu$ and $d\\mu$ atom scattering from the molecules H$_2$, HD and D$_2$. These cross sections include hyperfine transitions in the muonic atoms, the muon exchange between the nuclei $p$ and $d$, and rotational-vibrational transitions in the target molecules. The Monte Carlo results have been used for preparing the time-projection chamber for the high-precision measurement of the nuclear $\\mu^{-}$ capture in the ground-state $p\\mu$ atom, which is now underway at the Paul Scherrer Institute.

  18. Multiphoton ionization of the hydrogen atom exposed to circularly or linearly polarized laser pulses

    International Nuclear Information System (INIS)

    This paper studies the multiphoton ionization of the hydrogen atom exposed to the linearly or circularly polarized laser pulses by solving the time-dependent Schrödinger equation. It finds that the ratio of the ionization probabilities by linearly and circularly polarized laser pulses varies with the numbers of absorbing photons. With the same laser intensity, the circularly polarized laser pulse favors to ionize the atom with more ease than the linearly polarized laser pulse if only two or three photons are necessary to be absorbed. For the higher order multiphoton ionization, the linearly polarized laser pulse has the advantage over circularly polarized laser pulse to ionize the atom. (atomic and molecular physics)

  19. The dynamical properties of Rydberg hydrogen atom near a metal surface

    Institute of Scientific and Technical Information of China (English)

    GE Meihua; ZHANG Yanhui; WANG Dehua; DU Mengli; LIN Shenglu

    2005-01-01

    The dynamical properties of Rydberg hydrogen atom near a metal surface are presented by using the methods of phase space analysis and closed orbit theory. Transforming the coordinates of the Hamiltonian, we find that the phase space of the system is divided into vibrational and rotational region. Both the Poincaré surface of section and the closed orbit theory verify the same conclusion clearly. In this paper we choose the atomic principal quantum number as n = 20. The dynamical character of the exited hydrogen atom depends sensitively on the atom-surface distance d. When d is sufficiently large, the atom-surface potential can be expressed by the traditional van der Waals force and the system is integrable. When d becomes smaller, there exists a critical value dc. For d > dc, the system is near-integrable and the motion is regular. While chaotic motion appears for d < dc, and the system tends to be non-integrable. The trajectories become unstable and the electron might be captured onto the metal surface.

  20. Effects of atomic geometry and electronic structure of platinum surfaces on molecular adsorbates studied by gap-mode SERS.

    Science.gov (United States)

    Hu, Jian; Tanabe, Masahiro; Sato, Jun; Uosaki, Kohei; Ikeda, Katsuyoshi

    2014-07-23

    Surface enhanced Raman scattering (SERS) spectra of organic monolayers were measured on various types of polycrystalline and single crystalline Pt substrates with nanometric or atomic surface features, including heteroepitaxial Pt monolayers, using sphere-plane type nanogap structures. Although atomic geometry and electronic structures of a metal surface significantly influence metal-molecule interactions, such effects are often hindered in conventional SERS measured on a roughened surface because of the spectral information averaging at various adsorption sites. In this study, the use of atomically defined Pt surfaces revealed detailed surface effects; the observed preferential adsorption geometry on each surface was well explained by atomic surface arrangements. The peak shift of the intramolecular vibration in the anchor group was in good agreement with the variation of the d-band center of Pt substrates. Moreover, in electrochemical SERS study the Stark shift of an extramolecular vibrational mode at around 400 cm(-1), which is not accessible in infrared absorption spectroscopy, was monitored on an atomically defined heteroepitaxial Pt monolayer electrode. PMID:24802029

  1. Positronium formation and ionization in slow positron-hydrogen atom collisions

    International Nuclear Information System (INIS)

    The electron capture and ionization processes in slow collisions of positrons with hydrogen atoms are considered within the advanced adiabatic approach to atomic collisions. The mass asymmetry of the (p,e-,e+) collision system is properly taken into account. The calculated positronium formation and ionization cross sections compare favourably with the available experimental data in the adiabatic energy region. It is shown that the potential energy curve of the 2p σ molecular state supports a quasi-bound level of the three-particle (p,e+,e-) system with an energy of -0.3 eV and decay width of 0.15 eV, approximately. (author)

  2. Multiphoton resonant ionization of hydrogen atom exposed to two-colour laser pulses

    International Nuclear Information System (INIS)

    This paper studies the multiphoton resonant ionization by two-colour laser pulses in the hydrogen atom by solving the time-dependent Schrodinger equation. By fixing the parameters of fundamental laser field and scanning the frequency of second laser field, it finds that the ionization probability shows several resonance peaks and is also much larger than the linear superposition of probabilities by applying two lasers separately. The enhancement of the ionization happens when the system is resonantly pumped to the excited states by absorbing two or more colour photons non-sequentially. (atomic and molecular physics)

  3. An Introduction to Multiphoton Ionization and Study of Ionization Rate of Hydrogen Atom

    International Nuclear Information System (INIS)

    From a semiclassical point of view, we discuss the problem of nonlinear interaction between electromagnetic radiation and atoms. The time-dependent Schroedinger equation for single electron systems is solved using perturbative technique to obtain transition probability. We also discuss higher order perturbation used in multiple processes where two or more quanta are emitted instead of a single photon. The approach is based on the assumption that the perturbation is small. From the transition probability ionization rate and absorption, the cross-section of hydrogen atoms is calculated. Variation in photon energy and field strength is analyzed. Variation of cross-section with photon energy is discussed.

  4. Computation for High Excited Stark Levels of hydrogen Atoms in Uniform Electric Fields

    Institute of Scientific and Technical Information of China (English)

    田人和

    2003-01-01

    We present a new method for the numerical calculation of exact complex eigenvalues of Schrodinger equations for a hydrogen atom in a uniform electric field. This method allows a direct calculation for complex eigenvalues without using any auxiliary treatment, such as the Breit-Wigner parametrization and the complex scale transformation,etc. The characteristics of high excited atoms in electric field have attracted extensive interest in experimental aspect, however, the existing theoretical calculation is only up to n = 40. Here we present the computation results ranging from n = 1 to 100. The data for n(<,_ ) 40 are in agreement with the results of other researchers.

  5. Resonance and interference phenomena in the photoionisation of a hydrogen atom in a uniform electric field

    International Nuclear Information System (INIS)

    The photoionisation cross section for a hydrogen atom placed in a uniform electric field is investigated as a function of the light frequency. Analytical formulae are obtained describing the cross section structure in various regions of photon energy and field strength. The Fano parametrisation of resonance peak is generalised for the overlapping resonance case. When the photon energy is close to the ionisation potential the resonance peaks are strongly asymmetrical. A comparison is made with experiments where the structure is observed in the photoionisation of sodium and rubidium atoms. (author)

  6. Evidence for alkali metal induced intermolecular acetylenic hydrogen atom transfer between hydrogen-bonded alkyne complexes in solid argon

    International Nuclear Information System (INIS)

    Condensation of acetylene, propyne, and 2-butyne/acetylene mixtures with heavy alkali metal atoms (Na, K, Cs) in an argon matrix at 15 K has led to the appearance of infrared absorptions due to ethylene, propylene, and trans-2-butene, respectively. These results stand in sharp contrast with the products obtained with lithium. Isotopic studies have shown that ethylene formation involved three different acetylene molecules and evidenced a difference in the product yield with hydrogen vs. deuterium as well as a preference for trans- vs. cis-C2H2D2 formation, which is discussed and rationalized by differences in the zero point energies for the different mixed deuterium isotopes of the intermediate vinyl radical. This trend is amplified by methyl substitution. Spectroscopic evidence was found in these experiments for cesium acetylide (Cs+C2H-) and a cesium-acetylene π complex, which are involved in the intermolecular acetylenic hydrogen atom transfer process. 26 references, 3 figures, 2 tables

  7. K-series X-ray yield measurement of kaonic hydrogen atoms in a gaseous target

    Science.gov (United States)

    Bazzi, M.; Beer, G.; Bellotti, G.; Berucci, C.; Bragadireanu, A. M.; Bosnar, D.; Cargnelli, M.; Curceanu, C.; Butt, A. D.; d'Uffizi, A.; Fiorini, C.; Ghio, F.; Guaraldo, C.; Hayano, R. S.; Iliescu, M.; Ishiwatari, T.; Iwasaki, M.; Levi Sandri, P.; Marton, J.; Okada, S.; Pietreanu, D.; Piscicchia, K.; Romero Vidal, A.; Sbardella, E.; Scordo, A.; Shi, H.; Sirghi, D. L.; Sirghi, F.; Tatsuno, H.; Vazquez Doce, O.; Widmann, E.; Zmeskal, J.

    2016-10-01

    We measured the K-series X-rays of the K- p exotic atom in the SIDDHARTA experiment with a gaseous hydrogen target of 1.3 g /l, which is about 15 times the ρSTP of hydrogen gas. At this density, the absolute yields of kaonic X-rays, when a negatively charged kaon stopped inside the target, were determined to be 0.012-0.003+0.004 for Kα and 0.043-0.011+0.012 for all the K-series transitions Ktot. These results, together with the KEK E228 experiment results, confirm for the first time a target density dependence of the yield predicted by the cascade models, and provide valuable information to refine the parameters used in the cascade models for the kaonic atoms.

  8. LETTER TO THE EDITOR: A formula for line strengths of hydrogenic atoms

    Science.gov (United States)

    Watson, James K. G.

    2006-07-01

    It is shown that the line strength for the transition n' n of a hydrogenic atom with nuclear charge Z is (in atomic units) S_{n^{\\prime}n}=2Z \\langle n^{\\prime},0\\vert r\\vert n,0\\rangle \\langle n,0\\vert r^2\\vert n^{\\prime},0\\rangle, where the 0s in the matrix elements are the values of the quantum number l. This agrees with the expression for the hydrogen intensities originally given by McLean (1932 Nature 129 25). Expressions for the general l-diagonal matrix elements of r and r2 are given in terms of hypergeometric functions, and their asymptotic approximations for large n and relatively small c = n' - n are shown to agree with the asymptotic formula for the oscillator strength.

  9. $K$-series X-rays yield measurement of kaonic hydrogen atoms in gaseous target

    CERN Document Server

    Bazzi, M; Bellotti, G; Berucci, C; Bragadireanu, A M; Bosnar, D; Cargnelli, M; Curceanu, C; Butt, A D; d'Uffizi, A; Fiorini, C; Ghio, F; Guaraldo, C; Hayanao, R S; Iliescu, M; Ishiwatari, T; Iwasaki, M; Sandri, P Levi; Marton, J; Okada, S; Pietreanu, D; Piscicchia, K; Vidal, A Romero; Sbardella, E; Scordo, A; Shi, H; Sirghi, D L; Sirghi, F; Tatsuno, H; Doce, O Vazquez; Widmann, E; Zmeskal, J

    2016-01-01

    We measured the $K$-series X-rays of the $K^{-}p$ exotic atom in the SIDDHARTA experiment with a gaseous hydrogen target of 1.3 g/l, which is about 15 times the $\\rho_{\\rm STP}$ of hydrogen gas. At this density, the absolute yields of kaonic X-rays, when a negatively charged kaon stopped inside the target, were determined to be 0.012$^{+0.004}_{-0.003}$ for $K_{\\alpha}$ and 0.043$^{+0.012}_{-0.011}$ for all the $K$-series transitions $K_{tot}$. These results, together with the KEK E228 experiment results, confirm for the first time a target density dependence of the yield predicted by the cascade models, and provide valuable information to refine the parameters used in the cascade models for the kaonic atoms.

  10. Three-photon transitions from ground state to bound states in atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Thayyullathil, Ramesh Babu [Department of Physics, Cochin University of Science and Technology, Cochin 682 022 (India); Radhakrishnan, R [Department of Physics, Cochin University of Science and Technology, Cochin 682 022 (India); Seema, M [Department of Physics, Indian Institute of Technology, New Delhi 110 016 (India)

    2003-08-08

    In this paper, we present an efficient alternative method for the evaluation of the three-photon transition matrix element in the dipole approximation from the ground state to bound states in atomic hydrogen. This method is a variation of the Dalgarno-Lewis method for the treatment of the second-order Stark effect in the hydrogen atom. In this approach, the infinite double sum over the complete set of states including the continuum states present in the third-order perturbation theory result is treated exactly. The closed analytical expression obtained for the matrix element, as a function of incident photon energy, clearly displays all singularities present in the original third-order perturbation theory result.

  11. Electron capture into the 3s state of atomic hydrogen by H+ on Kr and Xe

    International Nuclear Information System (INIS)

    Absolute cross sections for electron capture into the 3s state of atomic hydrogen have been measured for 10-150-keV proton impact on Kr and Xe. The experimental procedure involved the quantitative measurement of the Balmer-alpha radiation emitted by the spontaneous decay of fast hydrogen atoms in flight. The 3s-state radiation was identified by its characteristic lifetime. The cross sections for both target gases reach a maximum in the projectile energy range under consideration. The Xe cross sections are approximately 40% higher than those for Kr near 25 keV but are similar above 80 keV. These values are consistent with existing 3s cross-section measurements and with an n-3 scaling of existing total electron-capture cross sections in accordance with Born-approximation predictions

  12. Measurements of recombination coefficient of hydrogen atoms on plasma deposited thin films

    International Nuclear Information System (INIS)

    We have performed experiments in plasma afterglow in order to determine the recombination coefficients of plasma deposited thin films of tungsten and graphite. Plasma deposited films rather than bulk material were used in order to more closely emulate surface structure of plasma-facing material deposits in fusion reactors. We have also determined the recombination coefficient of 85250 borosilicate glass and Teflon. Plasma was created by means of a radio frequency generator in a mixture of argon and hydrogen at the pressures between 60 Pa and 280 Pa. The degree of dissociation of hydrogen molecules was found to be between 0.1 and 1. The H-atom density was measured by Fiber Optic Catalytic Probe. The recombination coefficient was determined by measuring the axial profile of the H-atom density and using Smith's side arm diffusion model. (author)

  13. Interstitial modification of palladium nanoparticles with boron atoms as a green catalyst for selective hydrogenation

    Science.gov (United States)

    Chan, Chun Wong Aaron; Mahadi, Abdul Hanif; Li, Molly Meng-Jung; Corbos, Elena Cristina; Tang, Chiu; Jones, Glenn; Kuo, Winson Chun Hsin; Cookson, James; Brown, Christopher Michael; Bishop, Peter Trenton; Tsang, Shik Chi Edman

    2014-12-01

    Lindlar catalysts comprising of palladium/calcium carbonate modified with lead acetate and quinoline are widely employed industrially for the partial hydrogenation of alkynes. However, their use is restricted, particularly for food, cosmetic and drug manufacture, due to the extremely toxic nature of lead, and the risk of its leaching from catalyst surface. In addition, the catalysts also exhibit poor selectivities in a number of cases. Here we report that a non-surface modification of palladium gives rise to the formation of an ultra-selective nanocatalyst. Boron atoms are found to take residence in palladium interstitial lattice sites with good chemical and thermal stability. This is favoured due to a strong host-guest electronic interaction when supported palladium nanoparticles are treated with a borane tetrahydrofuran solution. The adsorptive properties of palladium are modified by the subsurface boron atoms and display ultra-selectivity in a number of challenging alkyne hydrogenation reactions, which outclass the performance of Lindlar catalysts.

  14. Preliminary measurements of doubly differential cross sections for ejection of electrons from atomic hydrogen by 70 keV protons

    International Nuclear Information System (INIS)

    A Slevin atomic hydrogen source has been used to produce a thermal beam of H and H2 as a target for 70 keV protons. A method has been devised which yields atomic to molecular hydrogen cross section ratios. Since the electron ejection cross sections for H2 are known, the atomic hydrogen cross sections can be determined. The angular and energy ranges of the detected electrons, differential in angle and energy, are 20 degrees-160 degrees and 1.5-250 eV respectively

  15. Preliminary measurements of doubly differential cross sections for ejection of electrons from atomic hydrogen by 70 keV protons

    Energy Technology Data Exchange (ETDEWEB)

    Kerby, G.W.; Gealy, M.W.; Hsu, Y.Y.; Rudd, M.E. [Univ. of Nebraska, Lincoln, NB (United States)

    1993-05-01

    A Slevin atomic hydrogen source has been used to produce a thermal beam of H and H{sub 2} as a target for 70 keV protons. A method has been devised which yields atomic to molecular hydrogen cross section ratios. Since the electron ejection cross sections for H{sub 2} are known, the atomic hydrogen cross sections can be determined. The angular and energy ranges of the detected electrons, differential in angle and energy, are 20{degrees}-160{degrees} and 1.5-250 eV respectively.

  16. Two-photon ionization of atomic hydrogen above the one-photon ionization threshold

    Energy Technology Data Exchange (ETDEWEB)

    Jayadevan, A.P. [Department of Physics, Cochin University of Science and Technology, Kochi (India); Thayyullathil, Ramesh Babu [Department of Physics, Cochin University of Science and Technology, Kochi (India)]. E-mail: rbt@cusat.ac.in

    2001-02-28

    An alternative method is presented for the evaluation of the two-photon ionization transition amplitude and transition rates of atomic hydrogen in the ground state above the one-photon ionization threshold. In this approach it is straightforward to calculate the angular distribution of the emitted electrons. These angular distributions are plotted and calculated transition rates are compared with the previously reported results. (author)

  17. Relativistic Approach to the Hydrogen Atom in a Minimal Length Scenario

    CERN Document Server

    Francisco, R O; Fabris, J C; Nogueira, J A

    2014-01-01

    In this work we show that relativistic contributions to the ground state energy of the hydrogen atom arising from the presence of a minimal length introduced by a Lorentz-covariant algebra are more relevant than non-relativistic ones, and because of this the non-relativistic approach is not suitable. In addition, comparing our result with experimental data we can roughly estimate the upper bound for the minimal length value of the order $10^{-20}m$.

  18. Hydrogen-Like Atom Description in the Framework of Quantum Mechanics with Consequently Probabilistic Interpretation

    CERN Document Server

    Zhidkov, E P

    2000-01-01

    In the paper a research of spectrum of the energy operator of the hydrogen-like atom in quantum mechanics with non-negative quantum function of distribution (QFD) is carried out. As a principle spectral property of the Hamiltonian its essential spectrum has been established. We have not got the theoretical response on questions of the evaluation of numbers and quantities of eigenvalues, which do not belong the essential spectrum. A method of numerical searching to answer these questions has been proposed.

  19. Hydrogen-like atom description in the framework of quantum mechanics with consequently probabilistic interpretation

    International Nuclear Information System (INIS)

    A research of the spectrum of the energy operator of the hydrogen-like atom in quantum mechanics with non-negative quantum function of distribution (QFD) is carried out. As a principle spectral property of the Hamiltonian its essential spectrum has been established. We have not got the theoretical response on questions of the evaluation of numbers and quantities of eigenvalues, which do not belong the essential spectrum. A method of numerical searching to answer these questions has been proposed. (author)

  20. Enhanced initial growth of atomic-layer-deposited metal oxides on hydrogen-terminated silicon

    International Nuclear Information System (INIS)

    A route is presented for activation of hydrogen-terminated Si(100) prior to atomic layer deposition. It is based on our discovery from in situ infrared spectroscopy that organometallic precursors can effectively initiate oxide growth. Narrow nuclear resonance profiling and Rutherford backscattering spectrometry show that surface functionalization by pre-exposure to 108 Langmuir trimethylaluminum at 300 deg. C leads to enhanced nucleation and to nearly linear growth kinetics of the high-permittivity gate dielectrics aluminum oxide and hafnium oxide

  1. Laser-assisted multiphoton ionization of a hydrogen atom by electron impact

    OpenAIRE

    Deb, S. Ghosh; S Roy; Sinha, C.

    2008-01-01

    The dynamics of the electron impact multiphoton ionization of a hydrogen atom in the presence of an intense laser field has been studied theoretically, with a view to comparing (qualitatively) the results with the recent kinematically complete experiments of Horr et al [ Phys. Rev. Lett., vol. 94, 153201, (2005) ] for the He target. Significant laser modifications are noted in the present doubly (DDCS) and the fully differential cross sections (TDCS). For most of the explored kinematics (chos...

  2. Hydrogen atom donor compounds as contrast enhancers for black-and-white photothermographic and thermographic elements

    Science.gov (United States)

    Harring, Lori S.; Simpson, Sharon M.; Sansbury, Francis H.

    1997-01-01

    Hydrogen atom donor compounds are useful as contrast enhancers when used in combination with (i) hindered phenol developers, and (ii) trityl hydrazide and/or formyl-phenyl hydrazine co-developers, to produce ultra-high contrast black-and-white photothermographic and thermographic elements. The photothermographic and thermographic elements may be used as a photomask in a process where there is a subsequent exposure of an ultraviolet or short wavelength visible radiation-sensitive imageable medium.

  3. The Hydrogen Atom: a Review on the Birth of Modern Quantum Mechanics

    OpenAIRE

    Nanni, Luca

    2015-01-01

    The purpose of this work is to retrace the steps that were made by scientists of XX century, like Bohr, Schrodinger, Heisenberg, Pauli, Dirac, for the formulation of what today represents the modern quantum mechanics and that, within two decades, put in question the classical physics. In this context, the study of the electronic structure of hydrogen atom has been the main starting point for the formulation of the theory and, till now, remains the only real case for which the quantum equation...

  4. Thresholds to Chaos and Ionization for the Hydrogen Atom in Rotating Fields

    OpenAIRE

    Chandre, C; Farrelly, David; Uzer, T.

    2002-01-01

    We analyze the classical phase space of the hydrogen atom in crossed magnetic and circularly polarized microwave fields in the high frequency regime, using the Chirikov resonance overlap criterion and the renormalization map. These methods are used to compute thresholds to large scale chaos and to ionization. The effect of the magnetic field is a strong stabilization of a set of invariant tori which bound the trajectories and prevent stochastic ionization. In order to ionize, larger amplitude...

  5. Ericson fluctuations in the chaotic ionization of the hydrogen atom in crossed magnetic and electric fields

    International Nuclear Information System (INIS)

    We report exact quantum calculations for the hydrogen atom in crossed magnetic and electric fields. Employing the complex-coordinate-rotation method we are able to extend the calculations of eigenstates far into the continuum region. Calculated photoionization cross sections are found to exhibit strong Ericson fluctuations, a characteristic feature of chaotic scattering. This interpretation is supported by classical trajectory calculations which reveal a fractal dependence of the classical ionization time on the initial conditions

  6. Threshold ionization dynamics of the hydrogen atom in crossed electric and magnetic fields

    International Nuclear Information System (INIS)

    In crossed electric and magnetic fields the hydrogen atom undergoes a transition to chaotic scattering associated with a critical point in the Hamiltonian flow. The stability of the critical point is determined and leads to an accurate prediction of the transition to scattering that is independent of the magnetic-field strength. Nevertheless, observed variations in the apparent ionization threshold with magnetic-field strength are explained

  7. Ionization cross sections of state selective atomic hydrogen by impact of multiply charged ions

    International Nuclear Information System (INIS)

    Ionization cross sections of atomic hydrogen in ground state and in metastable 2s state in collision with bare projectiles over a wide energy range have been calculated. The final state wave function considers the distortion due to Coulomb fields of both the projectile and the target nucleus. The present calculated total ionization cross-section values show good accord with the measurements for He2+, Li3- and C6+ impact at intermediate and high energy region. (author)

  8. Phase space structures and ionization dynamics of hydrogen atom in elliptically polarized microwaves

    OpenAIRE

    Shchekinova, Elena; Chandre, Cristel; Uzer, Turgay

    2006-01-01

    International audience The multiphoton ionization of hydrogen atoms in a strong elliptically polarized microwave field exhibits complex features that are not observed for ionization in circular and linear polarized fields. Experimental data reveal high sensitivity of ionization dynamics to the small changes of the field polarization. The multidimensional nature of the problem makes widely used diagnostics of dynamics, such as Poincaré surfaces of section, impractical. We analyze the phase ...

  9. A realistic example of chaotic tunneling: The hydrogen atom inparallel static electric and magnetic fields

    OpenAIRE

    Delande, Dominique; Zakrzewski, Jakub

    2003-01-01

    Statistics of tunneling rates in the presence of chaotic classical dynamics is discussed on a realistic example: a hydrogen atom placed in parallel uniform static electric and magnetic fields, where tunneling is followed by ionization along the fields direction. Depending on the magnetic quantum number, one may observe either a standard Porter-Thomas distribution of tunneling rates or, for strong scarring by a periodic orbit parallel to the external fields, strong deviations from it. For the ...

  10. Trapping of atomic hydrogen in octasilsesquioxane cages by glow discharge treatment

    International Nuclear Information System (INIS)

    Hydrogen atoms are trapped in octasilsesquioxane ((RSiO3/2)8, R = H, CH3, i-butyl, etc.) cages by electric discharge treatment. The yield of the trapped hydrogen was evaluated to be 1.3 x 10-4 of cage unit by using ESR spectroscopy for (CH3SiO3/2)8 discharged for 4 minutes at room temperature. To obtain a comparable yield of the trapped hydrogen by γ-rays (60Co) irradiation, an absorbed dose of ca. 300 kGy is required, taking two days or more in general. The discharge technique is simple and extremely efficient compared to the conventional method of γ-ray radiolysis. (author)

  11. Methane Formation by Flame-Generated Hydrogen Atoms in the Flame Ionization Detector

    DEFF Research Database (Denmark)

    Holm, Torkil; Madsen, Jørgen Øgaard

    1996-01-01

    The precombustion degradation of organic compounds in the flame ionization detector has been studied (1) by heating the additives in hydrogen in a quartz capillary and analyzing the reaction products by GC and (2) by following the degradation of the additives in a hydrogen flame, by means of a thin...... fused silica probe inserted from the bottom of the flame and connected to the ion source of a mass spectrometer. The results show that the thermic hydrogenolysis of hydrocarbons at flame temperatures produces mixtures of methane, ethene, and ethyne. In the flame, however, ethyne, benzene, isobutane...... atoms, which are formed in the burning hydrogen and which diffuse into the inner core of the flame. The quantitative formation of methane appears to explain the "equal per carbon" rule for the detector response of hydrocarbons, since all carbons are "exchanged" for methane molecules....

  12. THE INFRARED SPECTRA OF POLYCYCLIC AROMATIC HYDROCARBONS WITH SOME OR ALL HYDROGEN ATOMS REMOVED

    Energy Technology Data Exchange (ETDEWEB)

    Bauschlicher, Charles W. Jr. [Entry Systems and Technology Division, Mail Stop 230-3, NASA Ames Research Center, Moffett Field, CA 94035 (United States); Ricca, Alessandra, E-mail: Charles.W.Bauschlicher@nasa.gov, E-mail: Alessandra.Ricca-1@nasa.gov [Carl Sagan Center, SETI Institute, 189 Bernardo Avenue, Mountain View, CA 94043 (United States)

    2013-10-20

    The loss of one hydrogen from C{sub 96}H{sub 24} does not significantly affect the infrared spectra of the neutral, cation, or anion. Excluding a very weak C-C stretching band at 5.1 μm, the loss of two adjacent duo hydrogens does not significantly affect the spectra compared with the parent. Removing all of the hydrogen atoms significantly increases the intensity of the new C-C stretching band, and, for the cation, shifts it to a longer (5.2 μm) wavelength. Observations show a feature near 5.25 μm, which has been attributed to overtone and combination bands from polycyclic aromatic hydrocarbons (PAHs). This current work suggests that dehydrogenated PAHs might also contribute to this band, but its weakness implies that fully dehydrogenated cationic or dicationic species are very rare.

  13. Hydrogenation of PAH cations: a first step towards H2 formation

    CERN Document Server

    Boschman, L; Cazaux, S; Schlathoelter, T; Hoekstra, R; Spaans, M; Gonzalez-Magana, O

    2012-01-01

    Molecular hydrogen is the most abundant molecule in the universe. A large fraction of H2 forms by association of hydrogen atoms adsorbed on polycyclic aromatic hydrocarbons (PAHs), where formation rates depend crucially on the H sticking probability. We have experimentally studied PAH hydrogenation by exposing coronene cations, confined in a radiofrequency ion trap, to gas phase atomic hydrogen. A systematic increase of the number of H atoms adsorbed on the coronene with the time of exposure is observed. Odd coronene hydrogenation states dominate the mass spectrum up to 11 H atoms attached. This indicates the presence of a barrier preventing H attachment to these molecular systems. For the second and fourth hydrogenation, barrier heights of 72 +- 6 meV and 40 +- 10 meV, respectively are found which is in good agreement with theoretical predictions for the hydrogenation of neutral PAHs. Our experiments however prove that the barrier does not vanish for higher hydrogenation states. These results imply that PAH ...

  14. Fate of accidental symmetries of the relativistic hydrogen atom in a spherical cavity

    Science.gov (United States)

    Al-Hashimi, M. H.; Shalaby, A. M.; Wiese, U.-J.

    2015-11-01

    The non-relativistic hydrogen atom enjoys an accidental SO(4) symmetry, that enlarges the rotational SO(3) symmetry, by extending the angular momentum algebra with the Runge-Lenz vector. In the relativistic hydrogen atom the accidental symmetry is partially lifted. Due to the Johnson-Lippmann operator, which commutes with the Dirac Hamiltonian, some degeneracy remains. When the non-relativistic hydrogen atom is put in a spherical cavity of radius R with perfectly reflecting Robin boundary conditions, characterized by a self-adjoint extension parameter γ, in general the accidental SO(4) symmetry is lifted. However, for R =(l + 1) (l + 2) a (where a is the Bohr radius and l is the orbital angular momentum) some degeneracy remains when γ = ∞ or γ =2/R. In the relativistic case, we consider the most general spherically and parity invariant boundary condition, which is characterized by a self-adjoint extension parameter. In this case, the remnant accidental symmetry is always lifted in a finite volume. We also investigate the accidental symmetry in the context of the Pauli equation, which sheds light on the proper non-relativistic treatment including spin. In that case, again some degeneracy remains for specific values of R and γ.

  15. Excursion, Roaming and Migration of Hydrogen Atom during Dissociation of Formaldehyde

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyungrae [Hankuk Univ. of Foreign Studies, Seoul (Korea, Republic of)

    2014-05-15

    Several interesting features in trajectory were observed in the direct dynamics study of formaldehyde dissociation above radical dissociation limit. The hydrogen atom deliberately placed on the radical dissociation path can turn around at some distance from C without completion of dissociation and return to HCO moiety, colliding with it just as in a radical-radical recombination and producing a highly energized molecule. Excursion of a hydrogen atom to a distance of 6-8 bohrs and migration of a hydrogen atom back and forth between C and O are two of the most interesting features exhibited by the energized molecule. A series of excursions is seen to lead to a different kind of dissociation resembling roaming-like dissociation characterized by high vibrational excitation of H{sub 2} fragment. It is suggested that excursion occurs due to involvement of two different force field systems that exhibit discontinuity in 6-8 bohrs from HCO moiety. We argue that roaming is a non-zero impact parameter version of the excursion.

  16. Muon transfer from muonic hydrogen to heavier atoms; Transfert de charge muonique

    Energy Technology Data Exchange (ETDEWEB)

    Dupays, A

    2004-06-01

    This work concerns muon transfer from muonic hydrogen to heavier atoms. Recently, a method of measurement of the hyperfine structure of ground-state muonic hydrogen based on the collision energy dependence of the muon transfer rate to oxygen has been proposed. This proposal is based on measurements which where performed at the Paul Scherrer Institute in the early nineties which indicate that the muon transfer from muonic hydrogen to oxygen increases by a factor of 4 going from thermal to 0.12 eV energies. The motivation of our calculations was to confirm this behaviour. To study the collision energy dependence of the muon transfer rate, we have used a time-independent close-coupling method. We have set up an hyperspherical elliptic formalism valid for nonzero total angular momentum which allows accurate computations of state-to-state reactive and charge exchange processes. We have applied this formalism to muon-transfer process to oxygen and neon. The comparison with experimental results is in both cases excellent. Finally, the neon transfer rate dependence with energy suggests to use neon instead of oxygen to perform a measurement of the hyperfine structure of muonic hydrogen. The results of accurate calculations of the muon transfer rates from muonic protium and deuterium atoms to nitrogen, oxygen and neon are also reported. Very good agreement with measured rates is obtained and for the three systems, the isotopic effect is perfectly reproduced. (author)

  17. On the combination of a low energy hydrogen atom beam with a cold multipole ion trap

    International Nuclear Information System (INIS)

    The first part of the activities of this thesis was to develop a sophisticated ion storage apparatus dedicated to study chemical processes with atomic hydrogen. The integration of a differentially pumped radical beam source into an existing temperature variable 22- pole trapping machine has required major modifications. Since astrophysical questions have been in the center of our interest, the introduction first gives a short overview of astrophysics and -chemistry. The basics of ion trapping in temperature variable rf traps is well-documented in the literature; therefore, the description of the basic instrument (Chapter 2) is kept rather short. Much effort has been put into the development of an intense and stable source for hydrogen atoms the kinetic energy of which can be changed. Chapter 3 describes this module in detail with emphasis on the integration of magnetic hexapoles for guiding the atoms and special treatments of the surfaces for reducing H-H recombination. Due to the unique sensitivity of the rf ion trapping technique, this instrument allows one to study a variety of reactions of astrochemical and fundamental interest. The results of this work are summarized in Chapter 4. Reactions of CO2+ with hydrogen atoms and molecules have been established as calibration standard for in situ determination of H and H2 densities over the full temperature range of the apparatus (10 K-300 K). For the first time, reactions of H- and D-atoms with the ionic hydrocarbons CH+, CH2+, and CH4+ have been studied at temperatures of interstellar space. A very interesting, not yet fully understood collision system is the interaction of protonated methane with H. The outlook presents some ideas, how to improve the new instrument and a few reaction systems are mentioned which may be studied next. (orig.)

  18. On the combination of a low energy hydrogen atom beam with a cold multipole ion trap

    Energy Technology Data Exchange (ETDEWEB)

    Borodi, Gheorghe

    2008-12-09

    The first part of the activities of this thesis was to develop a sophisticated ion storage apparatus dedicated to study chemical processes with atomic hydrogen. The integration of a differentially pumped radical beam source into an existing temperature variable 22- pole trapping machine has required major modifications. Since astrophysical questions have been in the center of our interest, the introduction first gives a short overview of astrophysics and -chemistry. The basics of ion trapping in temperature variable rf traps is well-documented in the literature; therefore, the description of the basic instrument (Chapter 2) is kept rather short. Much effort has been put into the development of an intense and stable source for hydrogen atoms the kinetic energy of which can be changed. Chapter 3 describes this module in detail with emphasis on the integration of magnetic hexapoles for guiding the atoms and special treatments of the surfaces for reducing H-H recombination. Due to the unique sensitivity of the rf ion trapping technique, this instrument allows one to study a variety of reactions of astrochemical and fundamental interest. The results of this work are summarized in Chapter 4. Reactions of CO{sub 2}{sup +} with hydrogen atoms and molecules have been established as calibration standard for in situ determination of H and H{sub 2} densities over the full temperature range of the apparatus (10 K-300 K). For the first time, reactions of H- and D-atoms with the ionic hydrocarbons CH{sup +}, CH{sub 2}{sup +}, and CH{sub 4}{sup +} have been studied at temperatures of interstellar space. A very interesting, not yet fully understood collision system is the interaction of protonated methane with H. The outlook presents some ideas, how to improve the new instrument and a few reaction systems are mentioned which may be studied next. (orig.)

  19. A ``local observables'' method for wave mechanics applied to atomic hydrogen

    Science.gov (United States)

    Bowman, Peter J.

    2008-12-01

    An alternative method of deriving the values of the observables of atomic systems is presented. Rather than using operators and eigenvalues the local variables method uses the continuity equation together with current densities derived from wave functions that are solutions of the Dirac or Pauli equation. The method is applied to atomic hydrogen using the usual language of quantum mechanics rather than that of geometric algebra with which the method is often associated. The picture of the atom that emerges is one in which the electron density as a whole is rotating about a central axis. The results challenge some assumptions of conventional quantum mechanics. Electron spin is shown to be a property of the dynamical motion of the electron and not an intrinsic property of the electron, the ground state of hydrogen is shown to have an orbital angular momentum of ℏ, and excited states are shown to have angular momenta that are different from the eigenvalues of the usual quantum mechanical operators. The uncertainty relations are found not to be applicable to the orthogonal components of the angular momentum. No double electron spin gyromagnetic ratio is required to account for the observed magnetic moments, and the behavior of the atom in a magnetic field is described entirely in kinetic terms.

  20. High-multipole excitations of hydrogen-like atoms by twisted photons near a phase singularity

    Science.gov (United States)

    Afanasev, Andrei; Carlson, Carl E.; Mukherjee, Asmita

    2016-07-01

    We calculate transition amplitudes and cross sections for excitation of hydrogen-like atoms by the twisted photon states, or photon states with angular momentum projection on the direction of propagation exceeding ℏ. If the target atom is located at distances of the order of atomic size near the phase singularity in the vortex center, the transition rates into the states with orbital angular momentum {l}f\\gt 1 become comparable with the rates for electric dipole transitions. It is shown that when the transition rates are normalized to the local photon flux, the resulting cross sections for {l}f\\gt 1 are singular near the optical vortex center. The relation to the ‘quantum core’ concept introduced by Berry and Dennis is discussed.

  1. Non-perturbative calculations for the multiphoton ionization of hydrogen and lithium atoms

    International Nuclear Information System (INIS)

    Multiphoton ionization rates for the Hydrogen atom are calculated by direct solution of the time-dependent Schrodinger equation for several intensities at a photon energy of 5.0 eV (KrF laser). Ionization rates for linear polarized light are extracted front the time evolution of the ground state on a 2d cylindrical coordinate lattice, while rates for circular polarized light are extracted from calculations on a 3d Cartesian coordinate lattice. Multiphoton ionization rates for the Lithium atom are calculated in the frozen-core TDHF approximation for a variety of intensities and photon frequencies. The time-dependent equation for the valence HF orbital is solved on a 2d cylindrical coordinate lattice using both fixed and variable grid spacings. The non-perturbative results for both atoms are in sharp contrast to perturbation theory predictions

  2. Semiclassical Calculation of Recurrence Spectra of Rydberg Hydrogen Atom Near a Metal Surface

    Institute of Scientific and Technical Information of China (English)

    WANG De-Hua

    2009-01-01

    Using closed orbit theory, we give a clear physical picture description of the Rydberg hydrogen atom near a metal surface and calculate the Fourier transformed recurrence spectra of this system at different scaled energies below ionization threshold.The results show that with the increase of the scaled energy, the number of the closed orbit increases greatly.Some of the orbits are created by the bifurcation of the perpendicular orbit.This case is quite similar to the Rydberg atom in an electric field.When the scaled energy increases furthermore, chaotic orbits appear.This study provides a different perspective on the dynamical behavior of the Rydberg atom near a metal surface.

  3. High-Multipole Excitations of Hydrogen-Like Atoms by Twisted Photons near Phase Singularity

    CERN Document Server

    Afanasev, Andrei; Mukherjee, Asmita

    2016-01-01

    We calculate transition amplitudes and cross sections for excitation of hydrogen-like atoms by the twisted photon states, or photon states with angular momentum projection on the direction of propagation exceeding $\\hbar$. If the target atom is located at distances of the order of atomic size near the phase singularity in the vortex center, the transitions rates into the states with orbital angular momentum $l_f>1$ become comparable with the rates for electric dipole transitions. It is shown that when the transition rates are normalized to the local photon flux, the resulting cross sections for $l_f>1$ are singular near the optical vortex center. Relation to the "quantum core" concept introduced by Berry and Dennis is discussed.

  4. Preliminary measurements of doubly differential cross sections for ejection of electrons from atomic and molecular hydrogen by 70-keV helium ions

    International Nuclear Information System (INIS)

    A mixture of atomic and molecular hydrogen, generated by a Slevin hydrogen atom source, was used as the target for 70-keV He+ ions. Procedures were devised to extract the ratio of the cross sections for hydrogen atoms to hydrogen molecules. The cross sections for hydrogen molecules were then measured separately and the cross sections for hydrogen atoms obtained. The cross sections for ejection of electrons, differential in the angle and energy of ejection, were measured over the 15 degrees-160 degrees range of angles and at electron energies from 1.5 to 130 eV

  5. Preliminary measurements of doubly differential cross sections for ejection of electrons from atomic and molecular hydrogen by 70-keV helium ions

    Energy Technology Data Exchange (ETDEWEB)

    Hsu, Y.Y.; Gealy, M.W.; Kerby, G.W.; Rudd, M.E. [Univ. of Nebraska, Lincoln, NB (United States)

    1993-05-01

    A mixture of atomic and molecular hydrogen, generated by a Slevin hydrogen atom source, was used as the target for 70-keV He{sup +} ions. Procedures were devised to extract the ratio of the cross sections for hydrogen atoms to hydrogen molecules. The cross sections for hydrogen molecules were then measured separately and the cross sections for hydrogen atoms obtained. The cross sections for ejection of electrons, differential in the angle and energy of ejection, were measured over the 15{degrees}-160{degrees} range of angles and at electron energies from 1.5 to 130 eV.

  6. Physical reason for quantum behaviour of the electron and stability of the main state of the hydrogen atom

    International Nuclear Information System (INIS)

    An electron model is proposed explaining the physical reasons for its nonrelativistic quantum-mechanical behaviour, the origin of its own mechanical and magnetic momentum and field energy. As an example the main electron state in hydrogen atom is obtained

  7. Influence of an external field on the decay of coherently excited n = 2 states of the hydrogen atom

    International Nuclear Information System (INIS)

    We analyse the validity of the approximation of neglecting the 22S1/2-22P3/2 coupling in the description of the fluorescence from the n = 2 states of hydrogen atoms decaying in the presence of an external electric field. The results show the inadequacy of such an approach and point to the need for a re-interpretation of some previously reported experimental values of the state multipoles of the collisionally excited n = 2 hydrogen atoms. (Author)

  8. Three-dimensional simulation on explosions of hydrogen atomic clusters irradiated by an intense femtosecond laser pulse

    Institute of Scientific and Technical Information of China (English)

    Xia Yong; Liu Jian-Sheng; Ni Guo-Quan; Xu Zhi-Zhan

    2004-01-01

    Using classic particle dynamics simulations, the interaction process between an intense femtosecond laser pulse and icosahedral hydrogen atomic clusters H13, H55 and H147 has been studied. It is revealed that with increasing number of atoms in the cluster, the kinetic energy of ions generated in the Coulomb explosion of the ionized hydrogen clusters increases. The expansion process of the clusters after laser irradiation has also been examined, showing that the expansion scale decreases with increasing cluster size.

  9. Two-step adsorption on jungle-gym-type porous coordination polymers: dependence on hydrogen-bonding capability of adsorbates, ligand-substituent effect, and temperature.

    Science.gov (United States)

    Uemura, Kazuhiro; Yamasaki, Yukari; Onishi, Fumiaki; Kita, Hidetoshi; Ebihara, Masahiro

    2010-11-01

    A preliminary study of isopropanol (IPA) adsorption/desorption isotherms on a jungle-gym-type porous coordination polymer, [Zn(2)(bdc)(2)(dabco)](n) (1, H(2)bdc = 1,4-benzenedicarboxylic acid, dabco =1,4-diazabicyclo[2.2.2]octane), showed unambiguous two-step profiles via a highly shrunk intermediate framework. The results of adsorption measurements on 1, using probing gas molecules of alcohol (MeOH and EtOH) for the size effect and Me(2)CO for the influence of hydrogen bonding, show that alcohol adsorption isotherms are gradual two-step profiles, whereas the Me(2)CO isotherm is a typical type-I isotherm, indicating that a two-step adsorption/desorption is involved with hydrogen bonds. To further clarify these characteristic adsorption/desorption behaviors, selecting nitroterephthalate (bdc-NO(2)), bromoterephthalate (bdc-Br), and 2,5-dichloroterephthalate (bdc-Cl(2)) as substituted dicarboxylate ligands, isomorphous jungle-gym-type porous coordination polymers, {[Zn(2)(bdc-NO(2))(2)(dabco)]·solvents}(n) (2 ⊃ solvents), {[Zn(2)(bdc-Br)(2)(dabco)]·solvents}(n) (3 ⊃ solvents), and {[Zn(2)(bdc-Cl(2))(2)(dabco)]·solvents}(n) (4 ⊃ solvents), were synthesized and characterized by single-crystal X-ray analyses. Thermal gravimetry, X-ray powder diffraction, and N(2) adsorption at 77 K measurements reveal that [Zn(2)(bdc-NO(2))(2)(dabco)](n) (2), [Zn(2)(bdc-Br)(2)(dabco)](n) (3), and [Zn(2)(bdc-Cl(2))(2)(dabco)](n) (4) maintain their frameworks without guest molecules with Brunauer-Emmett-Teller (BET) surface areas of 1568 (2), 1292 (3), and 1216 (4) m(2) g(-1). As found in results of MeOH, EtOH, IPA, and Me(2)CO adsorption/desorption on 2-4, only MeOH adsorption on 2 shows an obvious two-step profile. Considering the substituent effects and adsorbate sizes, the hydrogen bonds, which are triggers for two-step adsorption, are formed between adsorbates and carboxylate groups at the corners in the pores, inducing wide pores to become narrow pores. Interestingly, such

  10. Selective hydrogenation of 1,3-butadiene on platinum-copper alloys at the single-atom limit.

    Science.gov (United States)

    Lucci, Felicia R; Liu, Jilei; Marcinkowski, Matthew D; Yang, Ming; Allard, Lawrence F; Flytzani-Stephanopoulos, Maria; Sykes, E Charles H

    2015-01-01

    Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One promising approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum-copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C-C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions. PMID:26449766

  11. Hydrogenation of PAH cations : A first step towards H2 formation

    NARCIS (Netherlands)

    Boschman, L.; Reitsma, G.; Cazaux, S.; Schlathölter, Thomas; Hoekstra, R.; Spaans, M.; Gonzalez Magana, Olmo

    2012-01-01

    Molecular hydrogen is the most abundant molecule in the universe. A large fraction of H-2 forms by association of hydrogen atoms adsorbed on polycyclic aromatic hydrocarbons (PAHs), where formation rates depend crucially on the H sticking probability. We have experimentally studied PAH hydrogenation

  12. A Guided-Inquiry Lab for the Analysis of the Balmer Series of the Hydrogen Atomic Spectrum

    Science.gov (United States)

    Bopegedera, A. M. R. P.

    2011-01-01

    A guided-inquiry lab was developed to analyze the Balmer series of the hydrogen atomic spectrum. The emission spectrum of hydrogen was recorded with a homemade benchtop spectrophotometer. By drawing graphs and a trial-and-error approach, students discover the linear relationship presented in the Rydberg formula and connect it with the Bohr model…

  13. Simulation of the Cosmic Evolution of Atomic and Molecular Hydrogen in Galaxies

    CERN Document Server

    Obreschkow, D; De Lucia, G; Khochfar, S; Rawlings, S

    2009-01-01

    We present a simulation of the cosmic evolution of the atomic and molecular phases of the cold hydrogen gas in about 3e7 galaxies, obtained by post-processing the virtual galaxy catalog produced by (De Lucia et al. 2007) on the Millennium Simulation of cosmic structure (Springel et al. 2005). Our method uses a set of physical prescriptions to assign neutral atomic hydrogen (HI) and molecular hydrogen (H2) to galaxies, based on their total cold gas masses and a few additional galaxy properties. These prescriptions are specially designed for large cosmological simulations, where, given current computational limitations, individual galaxies can only be represented by simplistic model-objects with a few global properties. Our recipes allow us to (i) split total cold gas masses between HI, H2, and Helium, (ii) assign realistic sizes to both the HI- and H2-disks, and (iii) evaluate the corresponding velocity profiles and shapes of the characteristic radio emission lines. The results presented in this paper include ...

  14. Analysis of the differential cross section for the hydrogen atom ionization by fast electrons in an uniform electric field

    International Nuclear Information System (INIS)

    Quantitative analysis of the differential cross section for a hydrogen atom ionization by fast electrons in the Born nonrelativistic approximation in the external homogeneous electric field, is carried out. It is shown that the cross section obtained may essentially differ from the similar cross section of an isolated atom ionization by angular distribution of the secondary pulses, oscillation components and magnitude

  15. Physical and chemical nature of the scaling relations between adsorption energies of atoms on metal surfaces

    DEFF Research Database (Denmark)

    Calle-Vallejo, F.; Martínez, J. I.; García Lastra, Juan Maria;

    2012-01-01

    Despite their importance in physics and chemistry, the origin and extent of the scaling relations between the energetics of adsorbed species on surfaces remain elusive. We demonstrate here that scalability is not exclusive to adsorbed atoms and their hydrogenated species but rather a general...

  16. Repulsive tip tilting as the dominant mechanism for hydrogen bond-like features in atomic force microscopy imaging

    Science.gov (United States)

    Lee, Alex J.; Sakai, Yuki; Kim, Minjung; Chelikowsky, James R.

    2016-05-01

    Experimental atomic force microscopy (AFM) studies have reported distinct features in regions with little electron density for various organic systems. These unexpected features have been proposed to be a direct visualization of intermolecular hydrogen bonding. Here, we apply a computational method using ab initio real-space pseudopotentials along with a scheme to account for tip tilting to simulate AFM images of the 8-hydroxyquinoline dimer and related systems to develop an understanding of the imaging mechanism for hydrogen bonds. We find that contrast for the observed "hydrogen bond" feature comes not from the electrostatic character of the bonds themselves but rather from repulsive tip tilting induced by neighboring electron-rich atoms.

  17. Energy levels of hydrogen-like atoms and fundamental constants, pt 1

    CERN Document Server

    Dvoeglazov, V V; Tyukhtyaev, Y N; Dvoeglazov, Valeri V.; Faustov, Rudolf N.; Tyukhtyaev, Yuri N.

    1994-01-01

    The present review includes the description of theoretical methods for the investigations of the spectra of hydrogen-like systems. Various versions of the quasipotential approach and the method of the effective Dirac equation are considered. The new methods, which have been developed in the eighties, are described. These are the method for the investigation of the spectra by means of the quasipotential equation with the relativistic reduced mass and the method for a selection of the logarithmic corrections by means of the renormalization group equation. The special attention is given to the construction of a perturbation theory and the selection of graphs, whereof the contributions of different orders of $\\alpha$, the fine structure constant, to the energy of the fine and hyperfine splitting in a positronium, a muonium and a hydrogen atom could be calculated. In the second part of this article the comparison of the experimental results and the theoretical results concerning the wide range of topics is produce...

  18. Incident angle dependence of reactions between graphene and hydrogen atom by molecular dynamics simulation

    CERN Document Server

    Saito, Seiki; Nakamura, Hiroaki

    2009-01-01

    Incident angle dependence of reactions between graphene and hydrogen atoms are obtained qualitatively by classical molecular dynamics simulation under the NVE condition with modified Brenner reactive empirical bond order (REBO) potential. Chemical reaction depends on two parameters, i.e., polar angle $\\theta$ and azimuthal angle $\\phi$ of the incident hydrogen. From the simulation results, it is found that the reaction rates strongly depend on polar angle $\\theta$. Reflection rate becomes larger with increasing $\\theta$, and the $\\theta$ dependence of adsorption rate is also found. The $\\theta$ dependence is caused by three dimensional structure of the small potential barrier which covers adsorption sites. $\\phi$ dependence of penetration rate is also found for large $\\theta$.

  19. Multiply Confined Nickel Nanocatalysts Produced by Atomic Layer Deposition for Hydrogenation Reactions.

    Science.gov (United States)

    Gao, Zhe; Dong, Mei; Wang, Guizhen; Sheng, Pei; Wu, Zhiwei; Yang, Huimin; Zhang, Bin; Wang, Guofu; Wang, Jianguo; Qin, Yong

    2015-07-27

    To design highly efficient catalysts, new concepts for optimizing the metal-support interactions are desirable. Here we introduce a facile and general template approach assisted by atomic layer deposition (ALD), to fabricate a multiply confined Ni-based nanocatalyst. The Ni nanoparticles are not only confined in Al2 O3 nanotubes, but also embedded in the cavities of Al2 O3 interior wall. The cavities create more Ni-Al2 O3 interfacial sites, which facilitate hydrogenation reactions. The nanotubes inhibit the leaching and detachment of Ni nanoparticles. Compared with the Ni-based catalyst supported on the outer surface of Al2 O3 nanotubes, the multiply confined catalyst shows a striking improvement of catalytic activity and stability in hydrogenation reactions. Our ALD-assisted template method is general and can be extended for other multiply confined nanoreactors, which may have potential applications in many heterogeneous reactions.

  20. Activation of extended red emission photoluminescence in carbon solids by exposure to atomic hydrogen and UV radiation

    Science.gov (United States)

    Furton, Douglas G.; Witt, Adolf N.

    1993-01-01

    We report on new laboratory results which relate directly to the observation of strongly enhanced extended red emission (ERE) by interstellar dust in H2 photodissociation zones. The ERE has been attributed to photoluminescence by hydrogenated amorphous carbon (HAC). We are demonstrating that exposure to thermally dissociated atomic hydrogen will restore the photoluminescence efficiency of previously annealed HAC. Also, pure amorphous carbon (AC), not previously photoluminescent, can be induced to photoluminesce by exposure to atomic hydrogen. This conversion of AC into HAC is greatly enhanced by the presence of UV irradiation. The presence of dense, warm atomic hydrogen and a strong UV radiation field are characteristic environmental properties of H2 dissociation zones. Our results lend strong support to the HAC photoluminescence explanation for ERE.

  1. Hydrogen Gas Sensors Fabricated on Atomically Flat 4H-SiC Webbed Cantilevers

    Science.gov (United States)

    Neudeck, Philip G.; Spry, David J.; Trunek, Andrew J.; Evans, Laura J.; Chen, Liang-Yu; Hunter, Gary W.; Androjna, Drago

    2007-01-01

    This paper reports on initial results from the first device tested of a "second generation" Pt-SiC Schottky diode hydrogen gas sensor that: 1) resides on the top of atomically flat 4H-SiC webbed cantilevers, 2) has integrated heater resistor, and 3) is bonded and packaged. With proper selection of heater resistor and sensor diode biases, rapid detection of H2 down to concentrations of 20 ppm was achieved. A stable sensor current gain of 125 +/- 11 standard deviation was demonstrated during 250 hours of cyclic test exposures to 0.5% H2 and N2/air.

  2. Atomic and ionic spectrum lines below 2000A: hydrogen through argon

    Energy Technology Data Exchange (ETDEWEB)

    Kelly, R.L.

    1982-10-01

    A critical tabulation of observed spectral lines below 2000 angstroms has been prepared from the published literature up to July 1978. It is intended principally as an aid to those physicists and astronomers who deal with the spectra of highly stripped atoms. This report includes the first 18 elements, from hydrogen (including deuterium) through argon. The tabulation is divided into two main sections: the spectrum lines by spectrum, and a finding list. The entries for each element give the ionization species, ground state term, and ionization potential, as well as the best values of vacuum wavelength, intensity, and classification. A list of the pertinent references is appended at the end.

  3. Electron impact ionization of atomic hydrogen from the 1S and 2S states

    Energy Technology Data Exchange (ETDEWEB)

    Bartschat, K.; Bray, I.

    1996-05-01

    We present results from R-Matrix with Pseudo-States (RMPS) and Convergent Close-Coupling (CCC) calculations for electron impact total ionization of the 1S and 2S states of atomic hydrogen in the energy region from threshold to 100 eV. Particular attention is given to the near threshold region. We find the results for energies more than 2 eV above threshold to be in excellent agreement with the available experimental data. (authors). 19 refs., 3 figs.

  4. Interbasis expansion and SO(3) symmetry in the two-dimensional hydrogen atom.

    Energy Technology Data Exchange (ETDEWEB)

    Torres del Castillo, G.F.; Lopez Villanueva, A. [Universidad Autonoma de Puebla, Puebla (Mexico)

    2001-04-01

    Making use of the SO(3) symmetry of the two-dimensional hydrogen atom, each of the bases for the bound states formed by the separable solutions of the Schroedinger equation in polar and parabolic coordinates are expressed in terms of the other. [Spanish] Usando la simetria SO(3) del atomo de hidrogeno en dos dimensiones, cada una de las bases para los estados ligados formadas por las soluciones separables de la ecuacion de Schroedinger en coordenadas polares y parabolicas se expresan en terminos de la otra.

  5. Exposure of epitaxial graphene on SiC(0001) to atomic hydrogen.

    Science.gov (United States)

    Guisinger, Nathan P; Rutter, Gregory M; Crain, Jason N; First, Phillip N; Stroscio, Joseph A

    2009-04-01

    Graphene films on SiC exhibit coherent transport properties that suggest the potential for novel carbon-based nanoelectronics applications. Recent studies suggest that the role of the interface between single layer graphene and silicon-terminated SiC can strongly influence the electronic properties of the graphene overlayer. In this study, we have exposed the graphitized SiC to atomic hydrogen in an effort to passivate dangling bonds at the interface, while investigating the results utilizing room temperature scanning tunneling microscopy.

  6. Traces of Lorentz symmetry breaking in a hydrogen atom at ground state

    Science.gov (United States)

    Borges, L. H. C.; Barone, F. A.

    2016-02-01

    Some traces of a specific Lorentz symmetry breaking scenario in the ground state of the hydrogen atom are investigated. We use standard Rayleigh-Schrödinger perturbation theory in order to obtain the corrections to the ground state energy and the wave function. It is shown that an induced four-pole moment arises, due to the Lorentz symmetry breaking. The model considered is the one studied in Borges et al. (Eur Phys J C 74:2937, 2014), where the Lorentz symmetry is broken in the electromagnetic sector.

  7. Traces of Lorentz symmetry breaking in a hydrogen atom at ground state

    International Nuclear Information System (INIS)

    Some traces of a specific Lorentz symmetry breaking scenario in the ground state of the hydrogen atom are investigated. We use standard Rayleigh-Schroedinger perturbation theory in order to obtain the corrections to the ground state energy and the wave function. It is shown that an induced four-pole moment arises, due to the Lorentz symmetry breaking. The model considered is the one studied in Borges et al. (Eur Phys J C 74:2937, 2014), where the Lorentz symmetry is broken in the electromagnetic sector. (orig.)

  8. Electron capture by impact of highly partially stripped ions on hydrogen atom in low collision energies

    International Nuclear Information System (INIS)

    Based on the reaction windows of electron capture obtained by using the two-state Landau-Zener model, the electron capture processes in collision of bare ions and highly partially stripped ions with hydrogen atoms are analysed. The capture cross sections predicted by multichannel Landau-Zener method are reliable if the cross points between the initial and final diabatic potential energy curves are located in the corresponding reaction windows. The calculations by the multichannel Landau-Zener method show that the present theoretical results are in accord with the analyses for slow C3+ + H and 5+ + H collisions

  9. STEREO Observations of Energetic Neutral Hydrogen Atoms During the 2006 December 5 Solar Flare

    OpenAIRE

    Mewaldt, R A; Leske, R. A.; Stone, E. C.; Barghouty, A. F.; Labrador, A. W.; Cohen, C. M. S.; Cummings, A. C.; Davis, A J; von-Rosenvinge, T. T.; Wiedenbeck, M. E.

    2009-01-01

    We report the discovery of energetic neutral hydrogen atoms (ENAs) emitted during the X9 solar event of 2006 December 5. Beginning ~1 hr following the onset of this E79 flare, the Low Energy Telescopes (LETs) on both the STEREO A and B spacecraft observed a sudden burst of 1.6-15 MeV protons beginning hours before the onset of the main solar energetic particle event at Earth. More than 70% of these particles arrived from a longitude within ±10° of the Sun, consistent with the measurement reso...

  10. Multiphoton resonant ionization of hydrogen atom exposed to two-colour laser pulses

    Institute of Scientific and Technical Information of China (English)

    Wang Pei-Jie; Fang Yan

    2008-01-01

    This paper studies the multiphoton resonant ionization by two-colour laser pulses in the hydrogen atom by solving the time-dependent Schr(o)dinger equation.By fixing the parameters of fundamental laser field and scanning the frequency of second laser field,it finds that the ionization probability shows several resonance peaks and is also much larger than the linear superposition of probabilities by applying two lasers separately.The enhancement of the ionization happens when the system is resonantly pumped to the excited states by absorbing two or more colour photons non-sequentially.

  11. Ionisation of hydrogen-like atoms by a multiphoton absorption process

    International Nuclear Information System (INIS)

    The general expression for the amplitude of the probability of ionisation by a multiphoton absorption process is derived. Its non-relativistic limit is taken and the bipolar approximation is used for calculating the ionisation cross-section of hydrogen-like atoms. This latter involves the summation over intermediate virtual states by means of: a) a recursion relationship concerning angular functions, b) a particular technique which when applied to radial functions makes it possible to solve a system of inhomogeneous first-order differential equations. (authors)

  12. Traces of Lorentz symmetry breaking in a hydrogen atom at ground state

    Energy Technology Data Exchange (ETDEWEB)

    Borges, L.H.C. [Universidade Federal do ABC, Centro de Ciencias Naturais e Humanas, Santo Andre, SP (Brazil); Barone, F.A. [IFQ-Universidade Federal de Itajuba, Itajuba, MG (Brazil)

    2016-02-15

    Some traces of a specific Lorentz symmetry breaking scenario in the ground state of the hydrogen atom are investigated. We use standard Rayleigh-Schroedinger perturbation theory in order to obtain the corrections to the ground state energy and the wave function. It is shown that an induced four-pole moment arises, due to the Lorentz symmetry breaking. The model considered is the one studied in Borges et al. (Eur Phys J C 74:2937, 2014), where the Lorentz symmetry is broken in the electromagnetic sector. (orig.)

  13. The Hydrogen Atom: a Review on the Birth of Modern Quantum Mechanics

    CERN Document Server

    Nanni, Luca

    2015-01-01

    The purpose of this work is to retrace the steps that were made by scientists of XIX century, like Bohr, Schrodinger, Heisenberg, Pauli, Dirac, for the formulation of what today represents the modern quantum mechanics and that, within two decades, put in question the classical physics. In this context, the study of the electronic structure of hydrogen atom has been the main starting point for the formulation of the theory and, till now, remains the only real case for which the quantum equation of motion can be solved exactly. The results obtained by each theory will be discussed critically, highlighting limits and potentials that allowed the further development of the quantum theory.

  14. Hydrogen-atom attack on methyl viologen in aqueous solution studied by pulse radiolysis

    International Nuclear Information System (INIS)

    Using hydrogen at high pressures of up to 150 bar as an OH scavenger in aqueous MV2+ solutions (pH 1) it is possible to differentiate between two kinds of transient formed simultaneously by H-atom attack on methyl viologen. One of them is assigned to an H adduct on the N atom, MV+H+, with absorption bands identical to those of the radical cation, MV+. The MV+H+ species deprotonates forming the long-lived radical cation, MV+. The second type of transient produced is attributed to an H-adduct on the ring carbon, MV2+H, decaying by second-order kinetics. The formation of MV+ by electron transfer from the propan-2-ol radical has been reinvestigated (pH 0 to 7); its absorption spectrum does not change in this pH range. Rate constants and molar extinction coefficients are presented. (U.K.)

  15. A unified numerical model of collisional depolarization and broadening rates due to hydrogen atom collisions

    CERN Document Server

    Derouich, M; Barklem, P S

    2015-01-01

    Interpretation of solar polarization spectra accounting for partial or complete frequency redistribution requires data on various collisional processes. Data for depolarization and polarization transfer are needed but often missing, while data for collisional broadening are usually more readily available. Recent work by Sahal-Br\\'echot and Bommier concluded that despite underlying similarities in the physics of collisional broadening and depolarization processes, relationships between them are not possible to derive purely analytically. We aim to derive accurate numerical relationships between the collisional broadening rates and the collisional depolarization and polarization transfer rates due to hydrogen atom collisions. Such relationships would enable accurate and efficient estimation of collisional data for solar applications. Using earlier results for broadening and depolarization processes based on general (i.e. not specific to a given atom), semi-classical calculations employing interaction potentials...

  16. Hidden momentum in a hydrogen atom and the Lorentz force law

    CERN Document Server

    Filho, J S Oliveira

    2015-01-01

    By using perturbation theory, we show that an hydrogen atom with magnetic moment due to the orbital angular momentum of the electron has hidden momentum in the presence of an external electric field. This means that the atomic electronic cloud has a nonzero linear momentum in its center of mass rest frame due to a relativistic effect. This is completely analogous to the hidden momentum that a classical current loop has in the presence of an external electric field. We discuss that this effect is essential for the validity of the Lorentz force law in quantum systems. We also connect our results to the secular Abraham-Minkowski debate about the momentum of light in material media.

  17. Positronium formation and ionization in slow positron-hydrogen atom collisions

    Energy Technology Data Exchange (ETDEWEB)

    Janev, R.K. [International Atomic Energy Agency, PO Box 100, A-1400 Vienna (Austria); Solov' ev, E.A. [Research Centre for Energy and Informatics, Macedonian Academy of Sciences and Arts, PO Box 428, 9100 Skopje (Macedonia, The Former Yugoslav Republic of)

    1999-07-14

    The electron capture and ionization processes in slow collisions of positrons with hydrogen atoms are considered within the advanced adiabatic approach to atomic collisions. The mass asymmetry of the (p,e{sup -},e{sup +}) collision system is properly taken into account. The calculated positronium formation and ionization cross sections compare favourably with the available experimental data in the adiabatic energy region. It is shown that the potential energy curve of the 2p {sigma} molecular state supports a quasi-bound level of the three-particle (p,e{sup +},e{sup -}) system with an energy of -0.3 eV and decay width of 0.15 eV, approximately. (author)

  18. Resonance and interference phenomena in the photoionisation of a hydrogen atom in a uniform electric field

    International Nuclear Information System (INIS)

    The photoionisation cross section for a hydrogen atom placed in a uniform electric field is calculated using separation of the variables in parabolic coordinates and the semiclassical approximation with account for the tunnelling and reflection above the top of the potential barrier. The equations defining the resonance positions and widths are obtained and analysed for energies below and above the potential barrier. The analytical expressions for the parameters of resonances lying above the barrier are obtained for the first time. It is shown that in the vicinity of the resonance the cross section can be well parametrised by Fano's formula. The approximate expressions for the profile index are deduced. The analytical results are compared with numerical calculation data. The recent experiments on the photoionisation of rubidium and sodium atoms are discussed. (author)

  19. On the role of atomic metastability in the production of Balmer line radiation from ‘cold’ atomic hydrogen, deuterium and hydrogenic ion impurities in fusion edge plasmas

    Science.gov (United States)

    Hey, J. D.

    2012-03-01

    Published arguments, which assign an important role to atomic metastability in the production of ‘narrow’ Zeeman component radiation from the boundary region of fusion plasmas, are examined critically in relation to l-redistribution by proton and electron collisions, and mixing of unperturbed atomic states by the ion microfield and microfield gradient. It is concluded that these important processes indeed severely constrain the contribution from ‘metastable’ states to the generation of the hydrogen Balmer spectra, for electron concentrations above 1012 cm-3, as pointed out before by the present author (Hey et al 1999 J. Phys. B: At. Mol. Opt. Phys. 32 3555). The analysis of collision-induced l-redistribution represents an extension of that used previously (Hey et al 1996 Contrib. Plasma Phys. 36 583), applicable up to higher electron densities. For comparison purposes, we also consider the question of metastability of ionized helium in a low-temperature plasma, and that of some common hydrogenic impurities (C5+ and Ne9+) in a hydrogen (deuterium) fusion plasma. While for low nuclear charge Z the metastability of 2s1/2 levels is quenched by the plasma environment, it is much reduced in high-Z ions owing to the rapid increase with Z of the two-photon electric dipole (2E1) and magnetic dipole (M1) spontaneous transition rates to the ground state, whereas the role of the plasma in these cases is less important. The main new principle elaborated in this work is the sensitivity of atomic line strengths, and hence collision strengths, to perturbation by the plasma environment for transitions between fine-structure sublevels of the same principal quantum number. As the plasma microfield strength grows, ‘allowed’ transitions diminish in strength, while ‘forbidden’ transitions grow. However, owing to violation of the parity selection rule, there is an overall loss of collision strength available to transitions, resulting from the appearance of significant

  20. Ab initio study of Ga-GaN system: Transition from adsorbed metal atoms to a metal–semiconductor junction

    Energy Technology Data Exchange (ETDEWEB)

    Witczak, Przemysław; Kempisty, Pawel; Strak, Pawel [Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw (Poland); Krukowski, Stanisław, E-mail: stach@unipress.waw.pl [Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw, Poland and Interdisciplinary Centre for Modelling, University of Warsaw, Pawińskiego 5a, 02-106 Warsaw (Poland)

    2015-11-15

    Ab initio studies of a GaN(0001)-Ga system with various thicknesses of a metallic Ga layer were undertaken. The studied systems extend from a GaN(0001) surface with a fractional coverage of gallium atoms to a Ga-GaN metal–semiconductor (m–s) contact. Electronic properties of the system are simulated using density functional theory calculations for different doping of the bulk semiconductor. It is shown that during transition from a bare GaN(0001) surface to a m–s heterostructure, the Fermi level stays pinned at a Ga-broken bond highly dispersive surface state to Ga–Ga states at the m–s interface. Adsorption of gallium leads to an energy gain of about 4 eV for a clean GaN(0001) surface and the energy decreases to 3.2 eV for a thickly Ga-covered surface. The transition to the m–s interface is observed. For a thick Ga overlayer such interface corresponds to a Schottky contact with a barrier equal to 0.9 and 0.6 eV for n- and p-type, respectively. Bond polarization-related dipole layer occurring due to an electron transfer to the metal leads to a potential energy jump of 1.5 eV, independent on the semiconductor doping. Additionally high electron density in the Ga–Ga bond region leads to an energy barrier about 1.2 eV high and 4 Å wide. This feature may adversely affect the conductivity of the n-type m–s system.

  1. Dynamic nuclear polarization and relaxation of H and D atoms in solid mixtures of hydrogen isotopes

    CERN Document Server

    Sheludiakov, S; Järvinen, J; Vainio, O; Lehtonen, L; Vasiliev, S; Lee, D M; Khmelenko, V V

    2016-01-01

    We report on a study of Dynamic Nuclear Polarization and electron and nuclear spin relaxation of atomic hydrogen and deuterium in solid molecular matrices of H$_{2}$, D$_{2}$, and HD mixtures. The electron and nuclear spin relaxation times ($T_{1e}$ and $T_{1N}$) were measured within the temperature range 0.15-2.5$\\,$K in a magnetic field of 4.6 T, conditions which ensure a high polarization of electron spins. We found that $T_{1e}$ is nearly temperature independent in this temperature range, while $T_{1N}$ decreased by 2 orders of magnitude. Such strong temperature dependence is typical for the nuclear Orbach mechanism of relaxation via the electron spins. We found that the nuclear spins of H atoms in solid D$_{2}$ and D$_{2}:$HD can be efficiently polarized by the Overhauser effect. Pumping the forbidden transitions of H atoms also leads to DNP, with the efficiency strongly dependent on the concentration of D atoms. This behaviour indicates the Cross effect mechanism of the DNP and nuclear relaxation, which...

  2. Two-dimensional quantum hydrogen atom in circularly polarized microwaves: Global properties

    Energy Technology Data Exchange (ETDEWEB)

    Zakrzewski, J.; Gebarowski, R.; Delande, D. [Instytut Fizyki Mariana Smoluchowskiego, Uniwersytet Jagiellonski, ulica Reymonta 4, 30-059 Krakow (Poland)]|[Laboratoire Kastler-Brossel, Universite Pierre et Marie Curie, T12, E1, 4 place Jussieu, 75252 Paris Cedex 05 (France)

    1996-07-01

    The ionization of hydrogen Rydberg atoms by {ital circularly} polarized microwaves is studied quantum mechanically in a model two-dimensional atom. We apply a combination of a transformation to the coordinate frame rotating with the field, with complex rotation approach and representation of the atomic subspace in a Sturmian-type basis. The diagonalization of resulting matrices allows us to treat exactly the ionization of atoms initially prepared in highly excited Rydberg states of principal quantum number {ital n}{sub 0}{approx_equal}60. Similarities and differences between ionization by circularly and linearly polarized microwaves are discussed with a particular emphasis on the high-frequency regime and on the localization phenomenon. The dependence of the ionization character on the initial state (circular, elliptical, or low angular momentum state) as well as on the helicity of the polarization is discussed in detail. It is shown that, in the high-frequency chaotic regime, close encounters with the nucleus do {ital not} play a major role in the ionization process. {copyright} {ital 1996 The American Physical Society.}

  3. Behavior of adsorbed diphenyl-sulfide on the Pd/C catalyst for o-chloronitrobenzene hydrogenation

    Institute of Scientific and Technical Information of China (English)

    Chang Su; Xiao-Nian Li; Qun-Feng Zhang; Lei Ma; Chun-Shan Lu; Feng Feng

    2013-01-01

    A series of diphenyl-sulfide (Ph2S)-immobilized Pd/C catalysts (Pd-Ph2S(x)/C) were prepared using the wetness-impregnation and immobilization method.Pd-Ph2S(x)/C catalysts employed for the hydrogenation of o-chloronitrobenzene showed very high selectivity.The structure of Pd-Ph2S(x)/C with different molar ratio of ligand (x-values) was characterized by XPS and TG-DSC-MS.The results suggest a "saturated" surface ratio of Ph2S/Pd (about 0.3) was formed on the Pd-Ph2S(x)/C catalysts surface.The Ph2S immobilized on the Pd particle is quite stable,and the desorption of Ph2S or dissociative loss of phenyl group was only found at temperatures above 500 K.The possible catalytic mechanism of the Pd-Ph2S(x)/C catalyst was also discussed.

  4. A probable vacuum state containing a large number of hydrogen atom of excited state or ground state K, Rb or Cs atom

    CERN Document Server

    You, Pei-Lin

    2008-01-01

    The linear Stark effect shows that the first excited state of hydrogen atom has large permanent electric dipole moment (EDM), d(H)=3eao (ao is Bohr radius). Using special capacitors our experiments discovered that the ground state K, Rb or Cs atom is polar atom with a large EDM of the order of eao as hydrogen atom of excited state. Their capacitance(C) at different voltage (V) was measured. The C-V curve shows that the saturation polarization of K, Rb or Cs vapor has be observed when the field E more than ten to the fifth power V/m. When the saturation polarization appeared, nearly all K, Rb or Cs atoms(more than 98 percent) turned toward the direction of the field, and C is approximately equal to Co (Co is vacuum capacitance) or their dielectric constant is nearly the same as vacuum! K, Rb or Cs vapor just exist in the lowest energy state, so we see the vacuum state containing a large number of atoms! Due to the saturation polarization of hydrogen vapor of excited state is easily appears, we conjecture that ...

  5. Enhanced binding capacity of boronate affinity adsorbent via surface modification of silica by combination of atom transfer radical polymerization and chain-end functionalization for high-efficiency enrichment of cis-diol molecules

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Wei; He, Maofang; Wang, Chaozhan; Wei, Yinmao, E-mail: ymwei@nwu.edu.cn

    2015-07-30

    Boronate affinity materials have been widely used for specific separation and preconcentration of cis-diol molecules, but most do not have sufficient capacity due to limited binding sites on the material surface. In this work, we prepared a phenylboronic acid-functionalized adsorbent with a high binding capacity via the combination of surface-initiated atom transfer radical polymerization (SI-ATRP) and chain-end functionalization. With this method, the terminal chlorides of the polymer chains were used fully, and the proposed adsorbent contains dense boronic acid polymers chain with boronic acid on the chain end. Consequently, the proposed adsorbent possesses excellent selectivity and a high binding capacity of 513.6 μmol g{sup −1} for catechol and 736.8 μmol g{sup −1} for fructose, which are much higher than those of other reported adsorbents. The dispersed solid-phase extraction (dSPE) based on the prepared adsorbent was used for extraction of three cis-diol drugs (i.e., epinephrine, isoprenaline and caffeic acid isopropyl ester) from plasma; the eluates were analyzed by HPLC-UV. The reduced amount of adsorbent (i.e., 2.0 mg) could still eliminate interferences efficiently and yielded a recovery range of 85.6–101.1% with relative standard deviations ranging from 2.5 to 9.7% (n = 5). The results indicated that the proposed strategy could serve as a promising alternative to increase the density of surface functional groups on the adsorbent; thus, the prepared adsorbent has the potential to effectively enrich cis-diol substances in real samples. - Highlights: • Boronate adsorbent is prepared via ATRP and chain-end functionalization. • The adsorbent has quite high binding capacity for cis-diols. • Binding capacity is easily manipulated by ATRP condition. • Chain-end functionalization can improve binding capacity significantly. • Reduced adsorbent is consumed in dispersed solid-phase extraction of cis-diols.

  6. Laser-Assisted Semi Relativistic Excitation of Atomic Hydrogen by Electronic Impact

    CERN Document Server

    Taj, S; Idrissi, M El; Oufni, L

    2012-01-01

    The excitation of H ($1s-2s$) by electron impact in the presence and in the absence of the laser field is studied in the framework of the first Born approximation. The angular variation of the laser-assisted differential cross section (DCS) for atomic hydrogen by electronic impact is presented at various kinetic energies for the incident electron. The use of Darwin wave function as a semirelativistic state to represent the atomic hydrogen gives interesting results when the condition $z/c\\ll1$ is fulfilled. A comparison with the non relativistic theory and experimental data gives good agreement. It was observed that beyond (2700 $eV$) which represents the limit between the two approaches, the non relativistic theory does not yield close agreement with our theory and that, over certain ranges of energy, it can be in error by several orders of magnitude. The sum rule given by Bunkin and Fedorov and by Kroll and Watson \\cite{22} has been verified in both nonrelativistic and relativistic regimes.

  7. Source of Atomic Hydrogen in the Atmosphere of HD 209458b

    CERN Document Server

    Liang, M C; Lee, A Y T; Yung, Y L; Liang, Mao-Chang; Parkinson, Christopher D.; Lee, Anthony Y.-T.; Yung, Yuk L.

    2003-01-01

    Atomic hydrogen loss at the top of HD 209458b's atmosphere has been recently detected Vidal-Madjar et al. 2003. We have developed a 1-dimensional model to study the chemistry in the upper atmosphere of this extrasolar "hot jupiter". The 3 most abundant elements (other than He), as well as 4 parent molecules are included in this model, viz., H, C, O, H2, CO, H2O, and CH4. The higher temperatures (~ 1000 K) and higher stellar irradiance (~6x10^5 W m^{-2}) strongly enhance and modify the chemical reaction rates in this atmosphere. Our two main results are that (a) the production of atomic hydrogen in the atmosphere is mainly driven by H2O photolysis and reaction of OH with H2, and is not sensitive to the exact abundances of CO, H2O, and CH4, and (b) H2O and CH4 can be produced via the photolysis of CO followed by the reactions with H2.

  8. Three-dimensional atomic mapping of hydrogenated polymorphous silicon solar cells

    Science.gov (United States)

    Chen, Wanghua; Pareige, Philippe; Roca i Cabarrocas, Pere

    2016-06-01

    Hydrogenated polymorphous silicon (pm-Si:H) is a nanostructured material consisting of silicon nanocrystals embedded in an amorphous silicon matrix. Its use as the intrinsic layer in thin film p-i-n solar cells has led to good cell properties in terms of stability and efficiency. Here, we have been able to assess directly the concentration and distribution of nanocrystals and impurities (dopants) in p-i-n solar cells, by using femtosecond laser-assisted atom probe tomography (APT). An effective sample preparation method for APT characterization is developed. Based on the difference in atomic density between hydrogenated amorphous and crystalline silicon, we are able to distinguish the nanocrystals from the amorphous matrix by using APT. Moreover, thanks to the three-dimensional reconstruction, we demonstrate that Si nanocrystals are homogeneously distributed in the entire intrinsic layer of the solar cell. The influence of the process pressure on the incorporation of nanocrystals and their distribution is also investigated. Thanks to APT we could determine crystalline fractions as low as 4.2% in the pm-Si:H films, which is very difficult to determine by standard techniques, such as X-ray diffraction, Raman spectroscopy, and spectroscopic ellipsometry. Moreover, we also demonstrate a sharp p/i interface in our solar cells.

  9. Time-resolved Absorption Spectra of the Laser-dressed Hydrogen Atom

    Science.gov (United States)

    Murakami, Mitsuko; Chu, Shih-I.

    2013-05-01

    A theoretical study of the transient absorption spectra for the laser-dressed hydrogen atom based on the accurate numerical solution of the time-dependent Schrödinger equation is presented. The timing of absorption is controlled by the time delay between an isolated extreme ultraviolet (XUV) pulse and a dressing infrared (IR) field. We identify two different kinds of physical processes in the spectra. One is the formation of dressed states, signified by the appearance of sidebands between the XUV absorption lines separated by one IR-photon energy. We show that their population is maximized when the XUV pulse coincides with the zero-crossing of the IR field, and that their energy can be manipulated by using a chirped IR field. The other process is the dynamical AC Stark shift induced by the IR field and probed by the XUV pulse. Our calculations indicate that the accidental degeneracy of the hydrogen atom leads to the multiple splittings of each XUV absorption line whose separations change in response to a slowly-varying IR envelope. Furthermore, we observe the Autler-Townes doublets for the n=2 and 3 states using the 656 nm dressing field, but their separation does not agree with the prediction by the conventional 3-level model that neglects the dynamical AC Stark effects.

  10. Discovery of a Shell of Neutral Atomic Hydrogen Surrounding the Carbon Star IRC+10216

    CERN Document Server

    Matthews, L D; Bertre, T Le

    2015-01-01

    We have used the Robert C. Byrd Green Bank Telescope to perform the most sensitive search to date for neutral atomic hydrogen (HI) in the circumstellar envelope (CSE) of the carbon star IRC+10216. Our observations have uncovered a low surface brightness HI shell of diameter ~1300" (~0.8 pc), centered on IRC+10216. The HI shell has an angular extent comparable to the far ultraviolet-emitting astrosphere of IRC+10216 previously detected with the GALEX satellite, and its kinematics are consistent with circumstellar matter that has been decelerated by the local interstellar medium. The shell appears to completely surround the star, but the highest HI column densities are measured along the leading edge of the shell, near the location of a previously identified bow shock. We estimate a total mass of atomic hydrogen associated with IRC+10216 CSE of M_HI~3x10e-3 M_sun. This is only a small fraction of the expected total mass of the CSE (<1%) and is consistent with the bulk of the stellar wind originating in molec...

  11. The Transition from Atomic to Molecular Hydrogen in Interstellar Clouds: 21cm Signature of the Evolution of Cold Atomic Hydrogen in Dense Clouds

    CERN Document Server

    Goldsmith, P F; Krco, M; Goldsmith, Paul F.; Li, Di; Krco, Marko

    2006-01-01

    We have investigated the time scale for formation of molecular clouds by examining the conversion of HI to H2 using a time-dependent model. H2 formation on dust grains and cosmic ray and photo destruction are included in one-dimensional model slab clouds which incorporate time-independent density and temperature distributions. We calculate 21cm spectral line profiles seen in absorption against a background provided by general Galactic HI emission, and compare the model spectra with HI Narrow Self-Absorption, or HINSA, profiles absorbed in a number of nearby molecular clouds. The time evolution of the HI and H2 densities is dramatic, with the atomic hydrogen disappearing in a wave propagating from the central, denser regions which have a shorter H2 formation time scale, to the edges, where the density is lower and the time scale for H2 formation longer. The model 21cm spectra are characterized by very strong absorption at early times, when the HI column density through the model clouds is extremely large. The ...

  12. Emission of hydrogen energetic neutral atoms from the Martian subsolar magnetosheath

    Science.gov (United States)

    Wang, X.-D.; Alho, M.; Jarvinen, R.; Kallio, E.; Barabash, S.; Futaana, Y.

    2016-01-01

    We have simulated the hydrogen energetic neutral atom (ENA) emissions from the subsolar magnetosheath of Mars using a hybrid model of the proton plasma charge exchanging with the Martian exosphere to study statistical features revealed from the observations of the Neutral Particle Detectors on Mars Express. The simulations reproduce well the observed enhancement of the hydrogen ENA emissions from the dayside magnetosheath in directions perpendicular to the Sun-Mars line. Our results show that the neutralized protons from the shocked solar wind are the dominant ENA population rather than those originating from the pickup planetary ions. The simulation also suggests that the observed stronger ENA emissions in the direction opposite to the solar wind convective electric field result from a stronger proton flux in the same direction at the lower magnetosheath; i.e., the proton fluxes in the magnetosheath are not cylindrically symmetric. We also confirm the observed increasing of the ENA fluxes with the solar wind dynamical pressure in the simulations. This feature is associated with a low altitude of the induced magnetic boundary when the dynamic pressure is high and the magnetosheath protons can reach to a denser exosphere, and thus, the charge exchange rate becomes higher. Overall, the analysis suggests that kinetic effects play an important and pronounced role in the morphology of the hydrogen ENA distribution and the plasma environment at Mars, in general.

  13. Heterogeneous catalytic processes on cobalt, molybdenum and cobalt-molybdenum catalysts studied by temperature-programmed desorption and temperature-programmed reaction. 27 H-D exchange between adsorbed hydrogen and various coadsorbed molecules on the surface of Co-Mo catalysts

    International Nuclear Information System (INIS)

    The H-D-exchange between hydrogen adsorbed on the surface of reduced catalyst Co-Mo/Al2O3 and molecules of coadsorbates: D2O, benzene C6D6, cyclohexane C6D12 and propanethiol C3H7SH, has been studied under conditions of temperature-programmed reaction. It has been discovered that al the forms of hydrogen adsorbed on the catalyst take part in H-D-exchange. Spillover hydrogen adsorbed on a substrate features a high degree of Y-D-exchange with the coadsorbates mentioned. 2 refs., 6 figs

  14. Massive stars formed in atomic hydrogen reservoirs: HI observations of gamma-ray burst host galaxies

    CERN Document Server

    Michałowski, Michał J; Hjorth, J; Krumholz, M R; Tanvir, N R; Kamphuis, P; Burlon, D; Baes, M; Basa, S; Berta, S; Ceron, J M Castro; Crosby, D; D'Elia, V; Elliott, J; Greiner, J; Hunt, L K; Klose, S; Koprowski, M P; Floc'h, E Le; Malesani, D; Murphy, T; Guelbenzu, A Nicuesa; Palazzi, E; Rasmussen, J; Rossi, A; Savaglio, S; Schady, P; Sollerman, J; Postigo, A de Ugarte; Watson, D; van der Werf, P; Vergani, S D; Xu, D

    2015-01-01

    Long gamma-ray bursts (GRBs), among the most energetic events in the Universe, are explosions of massive and short-lived stars, so they pinpoint locations of recent star formation. However, several GRB host galaxies have recently been found to be deficient in molecular gas (H2), believed to be the fuel of star formation. Moreover, optical spectroscopy of GRB afterglows implies that the molecular phase constitutes only a small fraction of the gas along the GRB line-of-sight. Here we report the first ever 21 cm line observations of GRB host galaxies, using the Australia Telescope Compact Array, implying high levels of atomic hydrogen (HI), which suggests that the connection between atomic gas and star formation is stronger than previously thought, with star formation being potentially directly fuelled by atomic gas (or with very efficient HI-to-H2 conversion and rapid exhaustion of molecular gas), as has been theoretically shown to be possible. This can happen in low metallicity gas near the onset of star forma...

  15. Unified treatment of hadronic annihilation and protonium formation in slow collisions of antiprotons with hydrogen atoms

    Science.gov (United States)

    Sakimoto, Kazuhiro

    2013-07-01

    Antiproton (p¯) collisions with hydrogen atoms, resulting in the hadronic process of particle-antiparticle annihilation and the atomic process of protonium (p¯p) formation (or p¯ capture), are investigated theoretically. As the collision energy decreases, the collision time required for the p¯ capture becomes necessarily longer. Then, there is the possibility that the p¯-p annihilation occurs significantly before the p¯ capture process completes. In such a case, one can no longer consider the annihilation decay separately from the p¯ capture process. The present study develops a rigorous unified quantum-mechanical treatment of the annihilation and p¯ capture processes. For this purpose, an R-matrix approach for atomic collisions is extended to have complex-valued R-matrix elements allowing for the hadronic annihilation. Detailed calculations are carried out at low collision energies ranging from 10-8 to 10-1 eV, and the annihilation and the p¯ capture (total and product-state selected) cross sections are reported. Consideration is given to the difference between the direct annihilation occurring during the collision and the annihilation of p¯p occurring after the p¯ capture. The present annihilation process is also compared with the annihilation in two-body p¯+p collisions.

  16. Atomic transport at charged graphene: why hydrogen and oxygen are so different

    CERN Document Server

    Nguyen, Manh-Thuong

    2015-01-01

    Using density-functional calculations, we show that electron or hole doped graphene can strongly change the mobility of adsorbed atoms H and O. Interestingly, charge doping affects the diffusion of H and O in the opposite way, namely, electron doping increases/reduces while hole doping reduces/increases the diffusion barrier of H/O, respectively. Specifically, on neutral graphene the diffusion barriers of O and H are 0.74 and 1.01 eV, which are, upon a hole doping of $+5.9\\times10^{13}$ cm$^{-2}$, 0.90 and 0.77 eV, and upon an electron doping of $-5.9\\times10^{13}$ cm$^{-2}$, 0.38 and 1.36 eV, respectively. This means, within the harmonic transition state theory, at room temperature, the diffusion rate of O can be decreased or increased by 470 or 2.2$\\times 10^7$ times, and that of H can be increased or decreased by $10^5$ or $7\\times 10^7$ times, by that hole or electron doping level. The difference between the H and O cases is interpreted in terms of the difference in geometric and bonding changes upon char...

  17. State-to-State Kinetics of Molecular and Atomic Hydrogen Plasmas

    International Nuclear Information System (INIS)

    Full text: The activity in the Plasma Chemistry group in Bari is focused on state-to-state kinetic modeling of systems of interest for technological applications ranging from fusion (negative ion sources) to aerospace. Concerning the tools for the derivation of information on the dynamics of elementary processes, recent results include: 1) the implementation of a simplified theoretical approach, the similarity function, for the calculation of cross sections for electron-impact induced vibronic excitation in diatomic molecules with resolution on internal degrees of freedom, giving results that compares well both to theory and experiments in the case of e-H2 excitation and avoiding the high computational load of more accurate methods; 2) new implementation of the code for resonant processes in electron-molecule collisions (resonant vibrational excitation and dissociative attachment) for the investigation of isotopic effects, considering the different role for the three relevant resonances in e-H2 scattering; 3) the inclusion of non-adiabatic effects, due to coupling among different potential energy surface, in the QCT (quasi-classical trajectory) code for the treatment of H++H2 system, representing a new frontier including quantum effects in the dynamics; 4) the implementation of a numerical tool based on the Downhill Simplex Method for the deconvolution of rate coefficients to cross sections, validated in the case of well-known systems as H+H2; and 5) the code for the semi-classical treatment of heterogeneous processes of atom recombination at the surface, has been used for the investigation of isotopic effect in the Eley-Ridael mechanism of deuterium on graphite For the simulation of plasmo-chemical systems, two existing codes have been coupled, the collisional- radiative model, for an atomic hydrogen plasma under shock-wave condition, and the code for calculation of synthetic hydrogen spectrum, deriving plasma optical properties, i.e. emissivity and absorption

  18. Quenching of $para$-H$_2$ with an ultra-cold anti-hydrogen atom $\\bar{H}_{1s}$

    OpenAIRE

    Sultanov, Renat A.; Adhikari, Sadhan K.; Guster, Dennis

    2009-01-01

    In this work we report the results concerning calculations for quantum-mechanical rotational transitions in molecular hydrogen, H$_2$, induced by an ultra-cold ground state anti-hydrogen atom $\\bar{H}_{1s}$. The calculations are accomplished using a non-reactive close-coupling quantum-mechanical approach. The H$_2$ molecule is treated as a rigid rotor. The total elastic scattering cross section $\\sigma_{el}(\\epsilon)$ at energy $\\epsilon$, state-resolved rotational transition cross sections $...

  19. Influence of an external field on the decay of coherently excited n = 2 states of the hydrogen atom

    Energy Technology Data Exchange (ETDEWEB)

    Chwirot, S.; Legowski, S.; Zaremba, J.; Slevin, J.

    1989-05-14

    We analyse the validity of the approximation of neglecting the 2/sup 2/S/sub 1/2/-2/sup 2/P/sub 3/2/ coupling in the description of the fluorescence from the n = 2 states of hydrogen atoms decaying in the presence of an external electric field. The results show the inadequacy of such an approach and point to the need for a re-interpretation of some previously reported experimental values of the state multipoles of the collisionally excited n = 2 hydrogen atoms. (Author).

  20. Role of atomic hydrogen density and energy in low power chemical vapor deposition synthesis of diamond films

    International Nuclear Information System (INIS)

    Polycrystalline diamond films were synthesized on silicon substrates without diamond seeding by a very low power (∼40-80 W) microwave plasma continuous vapor deposition reaction of a mixture of helium-hydrogen-methane (48.2/48.2/3.6%) or argon-hydrogen-methane (17.5/80/2.5%). However, predominantly graphitic carbon films or no films formed when neon, krypton, or xenon was substituted for helium or argon. The films were characterized by time of flight secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and X-ray diffraction. It is proposed that each of He+ and Ar+ served as a catalyst with atomic hydrogen to form an energetic plasma since only plasmas having these ions in the presence of atomic hydrogen showed significantly broadened H α lines corresponding to an average hydrogen atom temperature of >100 eV as reported previously. It was found that not only the energy, but also the H density uniquely increases in He-H2 and Ar-H2 plasmas. Bombardment of the carbon surface by highly energetic hydrogen formed by the catalysis reaction may play a role in the formation of diamond. Then, by this novel pathway, the relevance of the CO tie line is eliminated along with other stringent conditions and complicated and inefficient techniques which limit broad application of the versatility and superiority of diamond thin film technology

  1. Bose-Einstein condensation and heat capacity of two-dimensional spin-polarized atomic hydrogen

    International Nuclear Information System (INIS)

    The static fluctuation approximation (SFA) is used to study the condensate fraction and the specific heat capacity of finite two-dimensional spin-polarized atomic hydrogen. It is found that Bose-Einstein condensation occurs in this system. The transition temperature at different densities decreases as the number of particles of the system increases. At low density, a sharp peak in the specific heat capacity is observed at the transition temperature. On the other hand, as the density of the system increases, the transition temperature becomes no longer well-defined, and a hump is observed in the specific heat capacity around the transition temperature. A qualitative comparison of our results to published results for finite Bose systems shows good agreement.

  2. Kinetic analysis of interstitial atomic hydrogen in a-Si:(H,O,N) and beryllia

    International Nuclear Information System (INIS)

    A method for interpreting thermal decay of interstitial atomic hydrogen Hoi produced by irradiation in a-Si: (H,O,N) and in beryllia was developed. The hypothesis of Hoi were produced from RH type molecules by irradiation effect and trapped in the interstitials of studied elements was considered. The hypothesis of the heating causes the disarming of Hoi, and can be retrapped, recombine with R matrices or react between themselves to form the H2 molecules. The kinetic equations were arranged by a schematic method for each proposed reaction. These equations were solved numerically by RungeKutta method. The adjust parameters show that the Hoi + Hoi -> H2 occurs only for beryllia, because the kinetic occurs at higher temperatures. All the parameters were adjusted to Arrhenius law, allowing to determine the activation energies for each process. (M.C.K.)

  3. Electron capture into the 4s state of atomic hydrogen by H+ impact on noble gases

    International Nuclear Information System (INIS)

    Cross sections for electron capture into the 4s state of hydrogen have been measured for 10--150-keV protons incident upon He, Ne, Ar, Kr, and Xe. The cross-section curves for each gas reach an apparent maximum in this projectile-energy range. The values for Kr and Xe are consistent with an n-3 scaling in previous 3s capture-cross-section measurements in this projectile range. The He, Ne, and Ar values are in excellent agreement with previously reported measurements above 60 keV but give consistently higher values than those measurements at the lower energies. There are no comparable Kr and Xe values in the literature. The shape and magnitude of the excitation functions for these gases indicate that the internal structure of the target atom is an important factor in the charge-transfer process

  4. Atomic layer deposition of aluminum sulfide thin films using trimethylaluminum and hydrogen sulfide

    International Nuclear Information System (INIS)

    Sequential exposures of trimethylaluminum and hydrogen sulfide are used to deposit aluminum sulfide thin films by atomic layer deposition (ALD) in the temperature ranging from 100 to 200 °C. Growth rate of 1.3 Å per ALD cycle is achieved by in-situ quartz crystal microbalance measurements. It is found that the growth rate per ALD cycle is highly dependent on the purging time between the two precursors. Increased purge time results in higher growth rate. Surface limited chemistry during each ALD half cycle is studied by in-situ Fourier transformed infrared vibration spectroscopy. Time of flight secondary ion-mass spectroscopy measurement is used to confirm elemental composition of the deposited films

  5. Rate of reaction of the hydrogen atom with nitrous oxide in ambient water

    Science.gov (United States)

    Kazmierczak, Lukasz; Swiatla-Wojcik, Dorota; Szala-Bilnik, Joanna; Wolszczak, Marian

    2016-08-01

    The reaction of the hydrogen atom with nitrous oxide has been investigated by pulse radiolysis of N2O-saturated 0.1 M HCl solution at room temperature (24±1 °C). The value of (9±2)×104 M-1 s-1 obtained for the reaction rate constant is between the early estimates 1×104 M-1 s-1 by Czapski and Jortner (1960) and 4.3×105 M-1 s-1 by Thomas (1969), and is much lower than 2×106 M-1 s-1 used recently (Janik et al., 2007; Ismail et al., 2013; Liu et al., 2015; Meesungnoen et al., 2015).

  6. Relativistic electronic dressing in laser-assisted ionization of atomic hydrogen by electron impact

    CERN Document Server

    Attaourti, Y

    2004-01-01

    Within the framework of the coplanar binary geometry where it is justified to use plane wave solutions for the study of the $(e,2e)$ reaction and in the presence of a circularly polarized laser field, we introduce as a first step the DVRPWBA1 (Dirac-Volkov Plane Wave Born Approximation1) where we take into account only the relativistic dressing of the incident and scattered electrons. Then, we introduce the DVRPWBA2 (Dirac-Volkov Plane Wave Born Approximation2) where we take totally into account the relativistic dressing of the incident, scattered and ejected electrons. We then compare the corresponding triple differential cross sections for laser-assisted ionization of atomic hydrogen by electron impact both for the non relativistic and the relativistic regime.

  7. Positron-impact ionisation of atomic hydrogen in the presence of a bichromatic laser field

    Institute of Scientific and Technical Information of China (English)

    Lou Jun; Li Shu-Min

    2010-01-01

    The positron impact-ionisation of atomic hydrogen in the presence of a linearly polarised bichromatic field is investigated in the first Born approximation.The field is composed of a fundamental frequency and its second harmonic.The state of positron in the field is described by the Volkov wavefunction,and the continuum state of the ejected electron is described by the Coulomb-Volkov wavefunction.The dressed ground state of target is a first order time-dependent perturbative wavefunction.The triple differential cross sections and their dependencies on laser field parameters are discussed and compared with the results modified by a monochromatic field.Numerical results show that the coherent phase control is significant and the laser-assisted ionisation cross sections caused by positron and electron are different.

  8. Propagation of light in low pressure ionised and atomic hydrogen. Application to astrophysics

    CERN Document Server

    Moret-Bailly, J

    2003-01-01

    The "Impulsive Stimulated Raman Scattering" (ISRS) performed using ultrashort laser pulses shifts the light frequencies. Tried using ordinary incoherent light, it keeps its qualitative properties except the nonlinearity due to the power of the laser pulses. The relative frequency shifts of the "Coherent Raman Effect on Incoherent Light" (CREIL) which is obtained do not depend on the intensity and, in a first approximation, on the frequency of the light. As CREIL does not blur the images and the spectra, its shifts may be confused with Doppler shifts. ISRS and CREIL are parametric effects which do not excite the matter, transferring energy from hot beams to cold beams; for CREIL, the cold light is thermal radiation which is heated. CREIL requires low pressure gases acting as catalysts. These gases must have Raman transitions in the radiofrequencies range: for instance H2+ or excited atomic hydrogen in a magnetic field. The spectral lines resulting from a simultaneous absorption (or emission) and CREIL have a w...

  9. Laser-assisted multiphoton ionization of a hydrogen atom by electron impact

    CERN Document Server

    Deb, S Ghosh; Sinha, C

    2008-01-01

    The dynamics of the electron impact multiphoton ionization of a hydrogen atom in the presence of an intense laser field has been studied theoretically, with a view to comparing (qualitatively) the results with the recent kinematically complete experiments of Horr et al [ Phys. Rev. Lett., vol. 94, 153201, (2005) ] for the He target. Significant laser modifications are noted in the present doubly (DDCS) and the fully differential cross sections (TDCS). For most of the explored kinematics (chosen in accordance with the experiment), the present binary peak intensity of the laser-assisted TDCS is significantly enhanced with respect to the field free ones, in agreement with the experiment but in contradiction with the existing first order theories. Importance of the multiphoton effects are also studied.

  10. Ionization of atomic hydrogen by protons in the presence of a laser field

    International Nuclear Information System (INIS)

    The ionization of atomic hydrogen by protons in the presence of a laser background is studied. We describe the initial and final states of the proton by plane waves, the state of the target by a dressed wavefunction obtained by time-dependent theory in the soft-photon approximation, and the state of the ejected electron by a two-centre Coulomb function modulated in time by the laser field in the same way as a plane wave. The laser-modified double differential cross sections for a geometry of laser polarization parallel to the incident cross section of the proton are calculated and compared with the laser-free results. For each small electron ejection angle, a critical point is found in the electron energy spectrum, behind which the cross section is notably enhanced. (author)

  11. The Quantum Black Hole as a Hydrogen Atom: Microstates Without Strings Attached

    CERN Document Server

    Hooft, Gerard t

    2016-01-01

    Applying an expansion in spherical harmonics, turns the black hole with its microstates into something about as transparent as the hydrogen atom was in the early days of quantum mechanics. It enables us to present a concise description of the evolution laws of these microstates, linking them to perturbative quantum field theory, in the background of the Schwarzschild metric. Three pieces of insight are obtained: One, we learn how the gravitational back reaction, whose dominant component can be calculated exactly, turns particles entering the hole, into particles leaving it, by exchanging the momentum- and position operators; two, we find out how this effect removes firewalls, both on the future and the past event horizon, and three, we discover that the presence of region II in the Penrose diagram forces a topological twist in the background metric, culminating in antipodal identification. Although a cut-off is required that effectively replaces the transverse coordinates by a lattice, the effect of such a cu...

  12. Phase-space structures and ionization dynamics of the hydrogen atom in elliptically polarized microwaves

    Science.gov (United States)

    Shchekinova, E.; Chandre, C.; Uzer, T.

    2006-10-01

    The multiphoton ionization of hydrogen atoms in a strong elliptically polarized microwave field exhibits complex features that are not observed for ionization in circular and linear polarized fields. Experimental data reveal high sensitivity of ionization dynamics to the small changes of the field polarization. The multidimensional nature of the problem makes widely used diagnostics of dynamics, such as Poincaré surfaces of section, impractical. We analyze the phase-space dynamics using the finite time stability analysis rendered by the fast Lyapunov indicators technique. The concept of zero-velocity surface is used to initialize the calculations and visualize the dynamics. Our analysis provides stability maps calculated for the initial energy at the maximum and below the saddle of the zero-velocity surface. We estimate qualitatively the dependence of ionization thresholds on the parameters of the applied field, such as polarization and scaled amplitude.

  13. Effectiveness of the statistical potential in the description of fermions in a worm-algorithm path-integral Monte Carlo simulation of 3He atoms placed on a 4He layer adsorbed on graphite.

    Science.gov (United States)

    Ghassib, Humam B; Sakhel, Asaad R; Obeidat, Omar; Al-Oqali, Amer; Sakhel, Roger R

    2012-01-01

    We demonstrate the effectiveness of a statistical potential (SP) in the description of fermions in a worm-algorithm path-integral Monte Carlo simulation of a few 3He atoms floating on a 4He layer adsorbed on graphite. The SP in this work yields successful results, as manifested by the clusterization of 3He, and by the observation that the 3He atoms float on the surface of 4He. We display the positions of the particles in 3D coordinate space, which reveal clusterization of the 3He component. The correlation functions are also presented, which give further evidence for the clusterization.

  14. Low temperature removal of surface oxides and hydrocarbons from Ge(100) using atomic hydrogen

    Science.gov (United States)

    Walker, M.; Tedder, M. S.; Palmer, J. D.; Mudd, J. J.; McConville, C. F.

    2016-08-01

    Germanium is a group IV semiconductor with many current and potential applications in the modern semiconductor industry. Key to expanding the use of Ge is a reliable method for the removal of surface contamination, including oxides which are naturally formed during the exposure of Ge thin films to atmospheric conditions. A process for achieving this task at lower temperatures would be highly advantageous, where the underlying device architecture will not diffuse through the Ge film while also avoiding electronic damage induced by ion irradiation. Atomic hydrogen cleaning (AHC) offers a low-temperature, damage-free alternative to the common ion bombardment and annealing (IBA) technique which is widely employed. In this work, we demonstrate with X-ray photoelectron spectroscopy (XPS) that the AHC method is effective in removing surface oxides and hydrocarbons, yielding an almost completely clean surface when the AHC is conducted at a temperature of 250 °C. We compare the post-AHC cleanliness and (2 × 1) low energy electron diffraction (LEED) pattern to that obtained via IBA, where the sample is annealed at 600 °C. We also demonstrate that the combination of a sample temperature of 250 °C and atomic H dosing is required to clean the surface. Lower temperatures prove less effective in removal of the oxide layer and hydrocarbons, whilst annealing in ultra-high vacuum conditions only removes weakly bound hydrocarbons. Finally, we examine the subsequent H-termination of an IBA-cleaned sample using XPS, LEED and ultraviolet photoelectron spectroscopy (UPS) in order to examine changes in the work function of Ge(100) upon hydrogenation.

  15. Structural and atoms-in-molecules analysis of hydrogen-bond network around nitroxides in liquid water

    Science.gov (United States)

    Houriez, Céline; Masella, Michel; Ferré, Nicolas

    2010-09-01

    In this study, we investigated the hydrogen-bond network patterns involving the NO moieties of five small nitroxides in liquid water by analyzing nanosecond scale molecular dynamics trajectories. To this end, we implemented two types of hydrogen-bond definitions, based on electronic structure, using Bader's atoms-in-molecules analysis and based on geometric criteria. In each definition framework, the nitroxide/water hydrogen-bond networks appear very variable from a nitroxide to another. Moreover, each definition clearly leads to a different picture of nitroxide hydration. For instance, the electronic structure-based definition predicts a number of hydrogen bonds around the nitroxide NO moiety usually larger than geometric structure-based ones. One particularly interesting result is that the strength of a nitroxide/water hydrogen bond does not depend on its linearity, leading us to question the relevance of geometric definition based on angular cutoffs to study this type of hydrogen bond. Moreover, none of the hydrogen-bond definitions we consider in the present study is able to quantitatively correlate the strength of nitroxide/water hydrogen-bond networks with the aqueous nitroxide spin properties. This clearly exhibits that the hydrogen-bonding concept is not reliable enough to draw quantitative conclusions concerning such properties.

  16. Substrate-adsorbate coupling in CO-adsorbed copper

    CERN Document Server

    Lewis, S P; Lewis, Steven P.; Rappe, Andrew M.

    1996-01-01

    The vibrational properties of carbon monoxide adsorbed to the copper (100) surface are explored within density functional theory. Atoms of the substrate and adsorbate are treated on an equal footing in order to examine the effect of substrate--adsorbate coupling. This coupling is found to have a significant effect on the vibrational modes, particularly the in-plane frustrated translation, which mixes strongly with substrate phonons and broadens into a resonance. The predicted lifetime due to this harmonic decay mechanism is in excellent quantitative agreement with experiment.

  17. Atomic-scale investigation of point defects and hydrogen-solute atmospheres on the edge dislocation mobility in alpha iron

    Energy Technology Data Exchange (ETDEWEB)

    Bhatia, M. A.; Solanki, K. N., E-mail: kiran.solanki@asu.edu [School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287 (United States); Groh, S. [Institute of Mechanics and Fluid Dynamics, TU Bergakademie Freiberg, Freiberg 09556 (Germany)

    2014-08-14

    In this study, we present atomistic mechanisms of 1/2 [111](11{sup ¯}0) edge dislocation interactions with point defects (hydrogen and vacancies) and hydrogen solute atmospheres in body centered cubic (bcc) iron. In metals such as iron, increases in hydrogen concentration can increase dislocation mobility and/or cleavage-type decohesion. Here, we first investigate the dislocation mobility in the presence of various point defects, i.e., change in the frictional stress as the edge dislocation interacts with (a) vacancy, (b) substitutional hydrogen, (c) one substitutional and one interstitial hydrogen, (d) interstitial hydrogen, (e) vacancy and interstitial hydrogen, and (f) two interstitial hydrogen. Second, we examine the role of a hydrogen-solute atmosphere on the rate of local dislocation velocity. The edge dislocation simulation with a vacancy in the compression side of the dislocation and an interstitial hydrogen atom at the tension side exhibit the strongest mechanical response, suggesting a higher potential barrier and hence, the higher frictional stress (i.e., ∼83% higher than the pure iron Peierls stress). In the case of a dislocation interacting with a vacancy on the compressive side, the vacancy binds with the edge dislocation, resulting in an increase in the friction stress of about 28% when compared with the Peierls stress of an edge dislocation in pure iron. Furthermore, as the applied strain increases, the vacancy migrates through a dislocation transportation mechanism by attaining a velocity of the same order as the dislocation velocity. For the case of the edge dislocation interacting with interstitial hydrogen on the tension side, the hydrogen atom jumps through one layer perpendicular to the glide plane during the pinning-unpinning process. Finally, our simulation of dislocation interactions with hydrogen show first an increase in the local dislocation velocity followed by a pinning of the dislocation core in the atmosphere, resulting in

  18. An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics

    Science.gov (United States)

    Pyzer-Knapp, Edward O.; Thompson, Hugh P. G.; Day, Graeme M.

    2016-01-01

    We present a re-parameterization of a popular intermolecular force field for describing intermolecular interactions in the organic solid state. Specifically we optimize the performance of the exp-6 force field when used in conjunction with atomic multipole electrostatics. We also parameterize force fields that are optimized for use with multipoles derived from polarized molecular electron densities, to account for induction effects in molecular crystals. Parameterization is performed against a set of 186 experimentally determined, low-temperature crystal structures and 53 measured sublimation enthalpies of hydrogen-bonding organic molecules. The resulting force fields are tested on a validation set of 129 crystal structures and show improved reproduction of the structures and lattice energies of a range of organic molecular crystals compared with the original force field with atomic partial charge electrostatics. Unit-cell dimensions of the validation set are typically reproduced to within 3% with the re-parameterized force fields. Lattice energies, which were all included during parameterization, are systematically underestimated when compared with measured sublimation enthalpies, with mean absolute errors of between 7.4 and 9.0%. PMID:27484370

  19. A comprehensive study on atomic layer deposition of molybdenum sulfide for electrochemical hydrogen evolution.

    Science.gov (United States)

    Kwon, Do Hyun; Jin, Zhenyu; Shin, Seokhee; Lee, Wook-Seong; Min, Yo-Sep

    2016-04-01

    Atomic layer deposition (ALD) has emerged as an efficient method to design and prepare catalysts with atomic precision. Here, we report a comprehensive study on ALD of molybdenum sulfide (MoSx) for an electrocatalytic hydrogen evolution reaction. By using molybdenum hexacarbonyl and dimethyldisulfide as the precursors of Mo and S, respectively, the MoSx catalysts are grown at 100 °C on porous carbon fiber papers (CFPs). The ALD process results in the growth of particle-like MoSx on the CFP due to the lack of adsorption sites, and its crystallographic structure is a mixture of amorphous and nano-crystalline phases. In order to unveil the intrinsic activity of the ALD-MoSx, the exchange current densities, Tafel slopes, and turnover frequencies of the catalysts grown under various ALD conditions have been investigated by considering the fractional surface coverage of MoSx on the CFP and catalytically-active surface area. In addition, the ALD-MoSx/CFP catalysts exhibit excellent catalytic stability due to the strong adhesion of MoSx on the CFP and the mixed phase. PMID:26973254

  20. Ionisation of Rydberg hydrogen atom near a metal surface by short pulse laser

    Institute of Scientific and Technical Information of China (English)

    Wang Lei; Yang Hai-Feng; Liu Xiao-Jun; Liu Hong-Ping

    2010-01-01

    In the ionisation of Rydberg hydrogen atoms near a metal surface,the electron will escape from the nucleus and arrive at the detector in a time sequence.This probability flux train relies on the initial electron wave packet irradiated by the laser pulse.For simplicity,the laser pulse is usually simplified to a delta function in energy domain,resulting in a sharp initial arrival time with an exponentially decaying tail at the detector.Actually and semiclassically,the initial outgoing wave should be modeled as an ensemble of trajectories propagating away from the atomic core in all directions with a range of launch times and a range of energies.In this case,each pulse in the pulse train is averaged out rather than a sharp profile.We examine how energy and time averaging of the electron wave packet affects the resolution of escaping electron pulses and study the energy dependence of the arrival time for each pulse in the ionisation train.An optimization condition for the laser pulse shape to generate narrow ionisation electron pulse in the train is obtained.The ionisation rates with various excitation energy are calculated also,which show the excitation to higher N Rydberg states will narrow the electron pulse as well.

  1. An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics.

    Science.gov (United States)

    Pyzer-Knapp, Edward O; Thompson, Hugh P G; Day, Graeme M

    2016-08-01

    We present a re-parameterization of a popular intermolecular force field for describing intermolecular interactions in the organic solid state. Specifically we optimize the performance of the exp-6 force field when used in conjunction with atomic multipole electrostatics. We also parameterize force fields that are optimized for use with multipoles derived from polarized molecular electron densities, to account for induction effects in molecular crystals. Parameterization is performed against a set of 186 experimentally determined, low-temperature crystal structures and 53 measured sublimation enthalpies of hydrogen-bonding organic molecules. The resulting force fields are tested on a validation set of 129 crystal structures and show improved reproduction of the structures and lattice energies of a range of organic molecular crystals compared with the original force field with atomic partial charge electrostatics. Unit-cell dimensions of the validation set are typically reproduced to within 3% with the re-parameterized force fields. Lattice energies, which were all included during parameterization, are systematically underestimated when compared with measured sublimation enthalpies, with mean absolute errors of between 7.4 and 9.0%. PMID:27484370

  2. Solar Wind Charge Exchange Studies Of Highly Charged Ions On Atomic Hydrogen

    International Nuclear Information System (INIS)

    Accurate studies of low-energy charge exchange (CX) are critical to understanding underlying soft X-ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H-like, and He-like ions of C, N, O and Ne, which are the dominant charge states for these heavier elements in the solar wind. Absolute total cross sections for single electron capture by H-like ions of C, N, O and fully-stripped O ions from atomic hydrogen have been measured in an expanded range of relative collision energies (5 eV/u-20 keV/u) and compared to previous H-oven measurements. The present measurements are performed using a merged-beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source installed on a high voltage platform at the Oak Ridge National Laboratory. For the collision energy range of 0.3 keV/u-3.3 keV/u, which corresponds to typical ion velocities in the solar wind, the new measurements are in good agreement with previous H-oven measurements. The experimental results are discussed in detail and compared with theoretical calculations where available.

  3. Electron capture by fully stripped high-Z projectiles from the hydrogen atom

    International Nuclear Information System (INIS)

    A single-channel distorted-wave approximation is used to calculate the one-electron capture cross section into an arbitrary state (nlm) of Ti22+, V23+, and Fe26+ from the ground state of a hydrogen atom. Since the interaction between the heavy projectile and the target electron is stronger, we represent the initial-channel wave function by a continuum distorted wave while the wave function in the final channel is taken to be a traveling atomic orbital. The nth partial cross sections are found to be in qualitative agreement with previous calculations for some other systems. It is found that at high energies the value nmax, where the nth partial cross section is maximum, is larger by a few steps than obtained from the nmax=Z3/4 model. However, for a fixed projectile nmax moves towards the smaller values as the energy increases. The l dependence of the cross sections are also studied at different energies at the corresponding nmax. We have further studied the mth partial cross sections at various energies and at the corresponding nmax for several l values. It is found that the contributions from higher m values are decreasing rapidly for m>5

  4. Ionization and excitation of the excited hydrogen atom in strong circularly polarized laser fields

    CERN Document Server

    Bauer, J H; O'Mahony, Patrick F; Piraux, Bernard; Warda, K

    2014-01-01

    In the recent work of Herath et al. [Phys. Rev. Lett. 109, 043004 (2012)] the first experimental observation of a dependence of strong-field ionization rate on the sign of the magnetic quantum number m (of the initial bound state (n,l.m)) was reported. The experiment with nearly circularly polarized light could not distinguish which sign of m favors faster ionization. We perform ab initio calculations for the hydrogen atom initially in one of the four bound sub states with the principal quantum number n=2 and irradiated by a short circularly polarized laser pulse of 800nm. In the intensity range of 10^12 to 10^13 Watts/cm^2 excited bound states play a very important role, but also up to some 10^15 Watts/cm^2 they can not be neglected in a full description of the laser-atom interaction. We explore the region that with increasing intensity switches from multiphoton to over the barrrier ionization and we find unlike in tunneling-type theories, that the ratio of ionization rates for electrons initially counter-ro...

  5. Status of Charge Exchange Cross Section Measurements for Highly Charged Ions on Atomic Hydrogen

    Science.gov (United States)

    Draganic, I. N.; Havener, C. C.; Schultz, D. R.; Seely, D. G.; Schultz, P. C.

    2011-05-01

    Total cross sections of charge exchange (CX) for C5+, N6+, and O7+ ions on ground state atomic hydrogen are measured in an extended collision energy range of 1 - 20,000 eV/u. Absolute CX measurements are performed using an improved merged-beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source mounted on a high voltage platform. In order to improve the problematic H+ signal collection for these exoergic CX collisions at low relative energies, a new double focusing electrostatic analyzer was installed. Experimental CX data are in good agreement with all previous H-oven relative measurements at higher collision energies. We compare our results with the most recent molecular orbital close-coupling (MOCC) and atomic orbital close-coupling (AOCC) theoretical calculations. Work supported by the NASA Solar & Heliospheric Physics Program NNH07ZDA001N, the Office of Fusion Energy Sciences and the Division of Chemical Sciences, Geosciences, and Biosciences, and the Office of Basic Energy Sciences of the U.S. DoE.

  6. Solar Wind Charge Exchange Studies Of Highly Charged Ions On Atomic Hydrogen

    Science.gov (United States)

    Draganić, I. N.; Seely, D. G.; McCammon, D.; Havener, C. C.

    2011-06-01

    Accurate studies of low-energy charge exchange (CX) are critical to understanding underlying soft X-ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H-like, and He-like ions of C, N, O and Ne, which are the dominant charge states for these heavier elements in the solar wind. Absolute total cross sections for single electron capture by H-like ions of C, N, O and fully-stripped O ions from atomic hydrogen have been measured in an expanded range of relative collision energies (5 eV/u-20 keV/u) and compared to previous H-oven measurements. The present measurements are performed using a merged-beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source installed on a high voltage platform at the Oak Ridge National Laboratory. For the collision energy range of 0.3 keV/u-3.3 keV/u, which corresponds to typical ion velocities in the solar wind, the new measurements are in good agreement with previous H-oven measurements. The experimental results are discussed in detail and compared with theoretical calculations where available.

  7. Photoionization microscopy of Rydberg hydrogen atom in a non-uniform electrical field

    Science.gov (United States)

    Shao-Hao, Cheng; De-Hua, Wang; Zhao-Hang, Chen; Qiang, Chen

    2016-06-01

    In this paper, we investigate the photoionization microscopy of the Rydberg hydrogen atom in a gradient electric field for the first time. The observed oscillatory patterns in the photoionization microscopy are explained within the framework of the semiclassical theory, which can be considered as a manifestation of interference between various electron trajectories arriving at a given point on the detector plane. In contrast with the photoionization microscopy in the uniform electric field, the trajectories of the ionized electron in the gradient electric field will become chaotic. An infinite set of different electron trajectories can arrive at a given point on the detector plane, which makes the interference pattern of the electron probability density distribution extremely complicated. Our calculation results suggest that the oscillatory pattern in the electron probability density distribution depends sensitively on the electric field gradient, the scaled energy and the position of the detector plane. Through our research, we predict that the interference pattern in the electron probability density distribution can be observed in an actual photoionization microscopy experiment once the external electric field strength and the position of the electron detector plane are reasonable. This study provides some references for the future experimental research on the photoionization microscopy of the Rydberg atom in the non-uniform external fields. Project supported by the National Natural Science Foundation of China (Grant No. 11374133) and the Project of Shandong Provincial Higher Educational Science and Technology Program, China (Grant No. J13LJ04).

  8. The influence hydrogen atom addition has on charge switching during motion of the metal atom in endohedral Ca@C60H4 isomers.

    Science.gov (United States)

    Raggi, G; Besley, E; Stace, A J

    2016-09-13

    Density functional theory has been applied in a study of charge transfer between an endohedral calcium atom and the fullerene cage in Ca@C60H4 and [Ca@C60H4](+) isomers. Previous calculations on Ca@C60 have shown that the motion of calcium within a fullerene is accompanied by large changes in electron density on the carbon cage. Based on this observation, it has been proposed that a tethered endohedral fullerene might form the bases of a nanoswitch. Through the addition of hydrogen atoms to one hemisphere of the cage it is shown that, when compared with Ca@C60, asymmetric and significantly reduced energy barriers can be generated with respect to motion of the calcium atom. It is proposed that hydrogen atom addition to a fullerene might offer a route for creating a bi-stable nanoswitch that can be fine-tuned through the selection of an appropriate isomer and number of atoms attached to the cage of an endohedral fullerene.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

  9. The influence hydrogen atom addition has on charge switching during motion of the metal atom in endohedral Ca@C60H4 isomers.

    Science.gov (United States)

    Raggi, G; Besley, E; Stace, A J

    2016-09-13

    Density functional theory has been applied in a study of charge transfer between an endohedral calcium atom and the fullerene cage in Ca@C60H4 and [Ca@C60H4](+) isomers. Previous calculations on Ca@C60 have shown that the motion of calcium within a fullerene is accompanied by large changes in electron density on the carbon cage. Based on this observation, it has been proposed that a tethered endohedral fullerene might form the bases of a nanoswitch. Through the addition of hydrogen atoms to one hemisphere of the cage it is shown that, when compared with Ca@C60, asymmetric and significantly reduced energy barriers can be generated with respect to motion of the calcium atom. It is proposed that hydrogen atom addition to a fullerene might offer a route for creating a bi-stable nanoswitch that can be fine-tuned through the selection of an appropriate isomer and number of atoms attached to the cage of an endohedral fullerene.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. PMID:27501967

  10. Coupled-Channel Investigation of the Collision of Protons and Antiprotons with Hydrogen- Like Atoms in the 2s States

    Institute of Scientific and Technical Information of China (English)

    Reda S. Tantawi

    2003-01-01

    The influence of the electric charge of both the projectile and the target nucleus on the cross section of the inelastic collision of protons and antiprotons with atoms is investigated at energies ranging from i to 2500 KeV. The impact parameter method is used to analyse the cross sections of the excitation of the n = 3 states of H atom and He+, Li2+ ions being initially in the excited 2s states. The calculated cross sections for hydrogen atoms are compared with the other theoretical results based on coupled-channels methods.

  11. Preparation of magnetic metal organic frameworks adsorbent modified with mercapto groups for the extraction and analysis of lead in food samples by flame atomic absorption spectrometry.

    Science.gov (United States)

    Wang, Yang; Chen, Huanhuan; Tang, Jie; Ye, Guiqin; Ge, Huali; Hu, Xiaoya

    2015-08-15

    A novel magnetic metal organic frameworks adsorbent modified with mercapto groups was synthesized and developed for extraction and spectrophotometric determination of trace lead. The adsorbent was characterized by Fourier transforms infrared spectrometer, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. The results indicated the adsorbents exhibited high adsorption capacities for lead due to the chelation mechanism between metal cations and mercapto groups. Meanwhile, the lead sorption onto the adsorbents could be easily separated from aqueous solution using a magnetic separation method. Under the optimal conditions, a linear calibration curve in the range from 1 to 20 μg L(-1) was achieved with an enrichment factor of 100. The limits of detection and quantitation for lead were found to be 0.29 and 0.97 μg L(-1), respectively. The developed method was successfully applied to the determination of trace amounts of lead in food samples and certified reference material with satisfactory results.

  12. Bifurcations in the hydrogen atom in the presence of a circularly polarized microwave field and a static magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Lanchares, V. [Departamento de Matematicas y Computacion, Universidad de La Rioja, 26004 Logrono (Spain); Inarrea, M.; Salas, J.P. [Area de Fisica Aplicada, Universidad de La Rioja, 26004 Logrono (Spain)

    1997-09-01

    In a classical model, the dynamics of the hydrogen atom subjected to a circularly polarized microwave field and a magnetic field is shown to belong to the family of so-called biparametric quadratic Hamiltonians. The energy-level structure is studied in terms of the parametric bifurcations. {copyright} {ital 1997} {ital The American Physical Society}

  13. Visualization of a Large Set of Hydrogen Atomic Orbital Contours Using New and Expanded Sets of Parametric Equations

    Science.gov (United States)

    Rhile, Ian J.

    2014-01-01

    Atomic orbitals are a theme throughout the undergraduate chemistry curriculum, and visualizing them has been a theme in this journal. Contour plots as isosurfaces or contour lines in a plane are the most familiar representations of the hydrogen wave functions. In these representations, a surface of a fixed value of the wave function ? is plotted…

  14. Use of a PhET Interactive Simulation in General Chemistry Laboratory: Models of the Hydrogen Atom

    Science.gov (United States)

    Clark, Ted M.; Chamberlain, Julia M.

    2014-01-01

    An activity supporting the PhET interactive simulation, Models of the Hydrogen Atom, has been designed and used in the laboratory portion of a general chemistry course. This article describes the framework used to successfully accomplish implementation on a large scale. The activity guides students through a comparison and analysis of the six…

  15. Interaction de l'atome d'hydrogene avec un champ laser intense et bref a derive de frequence

    Science.gov (United States)

    Ba, Harouna Sileye

    Nous presentons dans ce document une etude theorique de l'interaction entre l'atome d'hydrogene et un champ laser intense et bref a derive de frequence. Dans un premier temps, nous etablissons une methode basee sur les fonctions B-splines qui permet de decrire avec precision l'ensemble de la structure energetique du systeme atomique. Dans le second temps, nous developpons une approche non perturbative de type spectrale, basee sur la resolution exacte de l'equation de Schrodinger dependante du temps, pour decrire l'atome d'hydrogene en interaction avec un champ laser. Nous proposons particulierement une representation realiste d'une impulsion laser a derive de frequence. Finalement, nous etudions le processus d'ionisation au dessus du seuil de l'atome d'hydrogene soumis a une impulsion a derive de frequence. Nos resultats montrent que la derive de frequence laser permet de controler et d'optimiser le transfert de population de l'etat fondamental vers les etats electroniques intermediaires impliques dans le processus d'ionisation. Mots-cles : Atome d'hydrogene Fonctions B-splines Methode non perturbative spectrale Impulsion laser intense et breve Parametre de derive de frequence laser lonisation multiphotonique

  16. Corrigendum: "Extracting Closed Classical Orbits from Quantum Recurrence Spectra of a Non-Hydrogenic Atom in Parallel Electric and Magnetic Fields"

    Institute of Scientific and Technical Information of China (English)

    WANG De-Hua

    2010-01-01

    @@ In a paper published by us,[1] we studied how to extract the closed orbit of the non-hydrogenic atom in parallel electric and magnetic fields. However, there was another paper published in 1996 by Courtney,[2] which studied the initial conditions of closed classical orbits from quantum spectra of hydrogen atom in magnetic field.

  17. Measurement of intensity-dependent rates of above-threshold ionization (ATI) of atomic hydrogen at 248 nm

    International Nuclear Information System (INIS)

    Measured rates of multiphoton ionization (MPI) from the ground state of atomic hydrogen by a linearly polarized, subpicosecond KrF laser pulse at 248 nm wavelength are compared to predictions of lowest-order perturbation theory, Floquet theory, and Keldysh-Faisal-Reiss (KFR) theory with and without Coulomb correction for peak irradiance of 3 x 1012W/cm2 to 2 x 1014W/cm2. The Coulomb-corrected Keldysh model falls closest to the measured rates, the others being much higher or much lower. At 5 x 1013W/cm2, the number of ATI electrons decreased by a factor of approximately 40 with each additional photon absorbed. ATI of the molecular hydrogen background and of atoms from photodissociation of the molecules were also observed. The experiment employed a crossed-beam technique at ultrahigh vacuum with an rf-discharge atomic hydrogen source and a magnetic-bottle type electron time-of-flight spectrometer to count the electrons in the different ATI channels separately. The apparatus was calibrated to allow comparison of absolute as well as relative ionization rates to the theoretical predictions. This calibration involved measuring the distribution of irradiance in a focal volume that moved randomly and changed its size from time to time. A data collection system under computer control divided the time-of-flight spectra into bins according to the energy of each laser pulse. This is the first measurement of absolute rates of ATI in atomic hydrogen, and the first measurement of absolute test of MPI in atomic hydrogen without a large factor to account for multiple modes in the laser field. As such, the results of this work are important to the development of ATI theories, which presently differ by orders of magnitude in their prediction of the ionization rates. They are also important to recent calculations of temperatures in laser-heated plasmas, many of which incorporate KFR theory

  18. Photoexcitation and ionization of a hydrogen atom confined by a combined effect of a spherical box and Debye plasma

    International Nuclear Information System (INIS)

    The spectrum of the hydrogen atom confined by a relatively large radius spherical box and Debye plasma environment is obtained by solving the Schrödinger equation by using Bernstein-polynomials (B-polynomials). Response of such confined atoms to laser field is studied using non-perturbative Floquet method. Photoexcitation and ionization are found to depend on the confining parameters, such as radius of the confining spherical box and the screening parameter of Debye plasma. - Highlights: • Spherically confined hydrogen atom embedded in plasma environment is studied. • Response to continuous wave laser field is investigated using Floquet method. • Energy spectrum and oscillator strengths depend on confinement parameters. • Dressing of energy states leads to characteristic changes in system behavior

  19. NMR study of the FH⋯F hydrogen bond. Relation between hydrogen atom position and FH⋯F bond length

    Science.gov (United States)

    Panich, A. M.

    1995-07-01

    1H and 19F NMR study of (NH 4) 3BiBr 6NH 4Br·2NH 4HF 2 shows the bifluoride ion in this compound to be asymmetric with distances r( HF) = 1.042 ± 0.002 and R( FF) = 2.373 ± 0.008 Å. Existing NMR and neutron diffraction data for the FH⋯F hydrogen bond in solids have been studied to find a relation between the position of the hydrogen atom and FH⋯F bond length. Such a relation has been established and explained in the framework of the two-dimensional dynamic model of the hydrogen bond. The dependencies of r(AH) on R(AB) for the OH⋯O and FH⋯F bonds are shown to be similar.

  20. Path integral Monte Carlo simulations of H{sub 2} adsorbed to lithium-doped benzene: A model for hydrogen storage materials

    Energy Technology Data Exchange (ETDEWEB)

    Lindoy, Lachlan P.; Kolmann, Stephen J.; D’Arcy, Jordan H.; Jordan, Meredith J. T., E-mail: m.jordan@chem.usyd.edu.au [School of Chemistry, The University of Sydney, Sydney (Australia); Crittenden, Deborah L. [Department of Chemistry, University of Canterbury, Christchurch (New Zealand)

    2015-11-21

    Finite temperature quantum and anharmonic effects are studied in H{sub 2}–Li{sup +}-benzene, a model hydrogen storage material, using path integral Monte Carlo (PIMC) simulations on an interpolated potential energy surface refined over the eight intermolecular degrees of freedom based upon M05-2X/6-311+G(2df,p) density functional theory calculations. Rigid-body PIMC simulations are performed at temperatures ranging from 77 K to 150 K, producing both quantum and classical probability density histograms describing the adsorbed H{sub 2}. Quantum effects broaden the histograms with respect to their classical analogues and increase the expectation values of the radial and angular polar coordinates describing the location of the center-of-mass of the H{sub 2} molecule. The rigid-body PIMC simulations also provide estimates of the change in internal energy, ΔU{sub ads}, and enthalpy, ΔH{sub ads}, for H{sub 2} adsorption onto Li{sup +}-benzene, as a function of temperature. These estimates indicate that quantum effects are important even at room temperature and classical results should be interpreted with caution. Our results also show that anharmonicity is more important in the calculation of U and H than coupling—coupling between the intermolecular degrees of freedom becomes less important as temperature increases whereas anharmonicity becomes more important. The most anharmonic motions in H{sub 2}–Li{sup +}-benzene are the “helicopter” and “ferris wheel” H{sub 2} rotations. Treating these motions as one-dimensional free and hindered rotors, respectively, provides simple corrections to standard harmonic oscillator, rigid rotor thermochemical expressions for internal energy and enthalpy that encapsulate the majority of the anharmonicity. At 150 K, our best rigid-body PIMC estimates for ΔU{sub ads} and ΔH{sub ads} are −13.3 ± 0.1 and −14.5 ± 0.1 kJ mol{sup −1}, respectively.

  1. Muonium in Stishovite: Implications for the Possible Existence of Neutral Atomic Hydrogen in the Earth's Deep Mantle

    Science.gov (United States)

    Funamori, Nobumasa; Kojima, Kenji M.; Wakabayashi, Daisuke; Sato, Tomoko; Taniguchi, Takashi; Nishiyama, Norimasa; Irifune, Tetsuo; Tomono, Dai; Matsuzaki, Teiichiro; Miyazaki, Masanori; Hiraishi, Masatoshi; Koda, Akihiro; Kadono, Ryosuke

    2015-02-01

    Hydrogen in the Earth's deep interior has been thought to exist as a hydroxyl group in high-pressure minerals. We present Muon Spin Rotation experiments on SiO2 stishovite, which is an archetypal high-pressure mineral. Positive muon (which can be considered as a light isotope of proton) implanted in stishovite was found to capture electron to form muonium (corresponding to neutral hydrogen). The hyperfine-coupling parameter and the relaxation rate of spin polarization of muonium in stishovite were measured to be very large, suggesting that muonium is squeezed in small and anisotropic interstitial voids without binding to silicon or oxygen. These results imply that hydrogen may also exist in the form of neutral atomic hydrogen in the deep mantle.

  2. 原子氢推进剂研究进展%Research Progress of Atomic Hydrogen Propellant

    Institute of Scientific and Technical Information of China (English)

    齐琳琳; 孟洪波; 岳广涛

    2013-01-01

      Compared with the usual hydrogen-oxygen engine, the atomic propellant engine can improve specific impulse for hundreds of seconds. In this article, the prospect of launch vehicle with atomic hydrogen propellant was analyzed, the take-off mass and dry weight of atomic propellant launch vehicle were estimated,and an optimal solution of the atomic propellant hydrogen rocket was put forward. Also, the rocket engine performance was estimated in a wide range of mixing ratio, atomic state content of solid hydrogen particles, and content of liquid helium carrier. As a monopropellant, atomic hydrogen propellant can realize a lowest rocket take-off mass when the mixing ratio is zero. Atomic hydrogen propellants may bring a revolutionary leap to launch vehicle, but issue the challenge in cryogenic technology.%  与通常的氢氧发动机相比,采用原子氢推进剂可以使比冲提高几百秒。通过介绍运载火箭采用原子氢推进剂的发展前景、原子氢推进剂火箭的起飞质量和干重,以及原子氢推进剂火箭设计的最佳方案,在比较宽的混合比范围、固氢颗粒中原子态含量范围、液氦载体含量范围估算火箭发动机性能,可以得到混合比为0时,作为单元推进剂的火箭起飞质量最低。原子氢推进剂以其优良的比冲性能给航天运载器带来质的飞跃,但对低温技术提出挑战。

  3. Study of the anti-hydrogen atom and ion formation in the collisions antiproton-positronium

    International Nuclear Information System (INIS)

    The future CERN experiment called GBAR intends to measure the gravitational acceleration of antimatter on Earth using cold (neV) anti-hydrogen atoms undergoing a free fall. The experiment scheme first needs to cool anti-hydrogen positive ions, obtained thanks to two consecutive reactions occurring when an antiproton beam collides with a dense positronium cloud.The present thesis studies these two reactions in order to optimise the production of the anti-ions. The total cross sections of both reactions have been computed in the framework of a perturbation theory model (Continuum Distorted Wave - Final State), in the range 0 to 30 keV antiproton kinetic energy; several excited states of positronium have been investigated. These cross sections have then been integrated to a simulation of the interaction zone where antiprotons collide with positronium; the aim is to find the optimal experimental parameters for GBAR. The results suggest that the 2P, 3D or, to a lower extend, 1S states of positronium should be used, respectively with 2, less than 1 or 6 keV antiprotons. The importance of using short pulses of antiprotons has been underlined; the positronium will have to be confined in a tube of 20 mm length and 1 mm diameter. In the prospect of exciting the 1S-3D two-photon transition in positronium at 410 nm, a pulsed laser system had already been designed. It consists in the frequency doubling of an 820 nm pulsed titanium-sapphire laser. The last part of the thesis has been dedicated to the realisation of this laser system, which delivers short pulses (9 ns) of 4 mJ energy at 820 nm. (author)

  4. Multiphoton ionization of a metastable hydrogen atom by electron and positron impact and charge asymmetry

    International Nuclear Information System (INIS)

    Charge asymmetry is studied theoretically for multiphoton ionization (nγ e±, e e±) of a hydrogen atom from its metastable (2S) state using coplanar geometry. The external laser field is chosen to be single-mode, spatially homogeneous, linearly polarized with laser intensity that is quite high by laboratory standards. The continuum states of the impinging electron (e) or positron (e+) are represented by plane wave Volkov states, while the wavefunctions for the ejected electron and the scattered electron/positron are chosen to be of Coulomb-Volkov type. The dressed wavefunction for the metastable (2S) hydrogen is constructed in the framework of degenerate perturbation theory. Charge asymmetry is noted in the triple differential cross sections (TDCS) of the two projectiles both in the field-free (FF) and laser-assisted situations. The positron binary peak intensity is much higher than that of the electron, while the reverse is true for the recoil peak. As for the laser modifications, the single-photon TDCS exhibits a distinct four lobed structure in contrast to the FF (two lobed) and is highly suppressed w.r.t. the latter, while the multiphoton TDCS usually tends to approach the FF (with some exceptions), obeying the famous Kroll-Watson (KW) sum rule for both projectiles. For e+ impact, the electron capture to the continuum (ECC) effect is also studied (for the symmetric geometry), where enhancement is noted in both the single and multiphoton ECC peaks thereby deviating from the KW sum rules.

  5. Facile Isolation of Adsorbent-Free Long and Highly-Pure Chirality-Selected Semiconducting Single-Walled Carbon Nanotubes Using A Hydrogen-bonding Supramolecular Polymer

    Science.gov (United States)

    Toshimitsu, Fumiyuki; Nakashima, Naotoshi

    2015-12-01

    The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only the chiral- or chemically-purity while sacrificing the sem-SWNT intrinsic structural identities by applying strong ultra-sonication and/or chemical modifications. Toward the ultimate purification of the sem-SWNTs, here we report a mild-conditioned extraction of the sem-SWNTs using removable supramolecular hydrogen-bonding polymers (HBPs) that are composed of dicarboxylic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selective extraction. Replacing conventional strong sonication techniques by a simple shaking using HPBs was found to provide long sem-SWNTs (>2.0 μm) with a very high D/G ratio, which was determined by atomic force microscopy observations. The HBPs were readily removed from the nanotube surfaces by an outer stimulus, such as a change in the solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to propose possible structures for the HBP-wrapped sem-SWNTs, furthermore, the mechanism of the chiral selectivity for the sorted sem-SWNTs is well explained by the relationship between the molecular surface area and mass of the HBP/SWNT composites.

  6. Calculations of hydrogen atom multiphoton energy level shifts, transition amplitudes and ionization probabilities

    International Nuclear Information System (INIS)

    Analyses of the resonant multiphoton ionization of atoms require knowledge of ac Stark energy shifts and of multiphoton, bound-to-bound state, transition amplitudes. In this paper, we consider the three-photon photoionization of hydrogen atoms at frequencies that are at and surrounding the two-photon 1s to 2s resonance. AC energy shift sums of both the 1s and 2s states are calculated as a function of the laser frequency along with two-photon 1s → 2s resonant transition amplitude sums. These quantities are calculated using an extended version of a method, which has often been employed in a variety of ways, of calculating these sums by expressing them in terms of solutions to a variety of differential equations that are derived from the different sums being evaluated. We demonstrate how exact solutions are obtained to these differential equations, which lead to exact evaluations of the corresponding sums. A variety of different cases are analysed, some involving analytic continuation, some involving real number analysis and some involving complex number analysis. A dc Stark sum calculation of the 2s state is carried out to illustrate the case where analytic continuation, pole isolation and pole subtraction are required and where the calculation can be carried out analytically; the 2s state, ac Stark shift sum calculations involve a case where no analytic continuation is required, but where the solution to the differential equation produces complex numbers owing to the finite photoionization lifetime of the 2s state. Results from these calculations are then used to calculate three-photon ionization probabilities of relevance to an analysis of the multiphoton ionization data published by Kyrala and Nichols (1991 Phys. Rev. A 44, R1450)

  7. Atoms

    Institute of Scientific and Technical Information of China (English)

    刘洪毓

    2007-01-01

    Atoms(原子)are all around us.They are something like the bricks (砖块)of which everything is made. The size of an atom is very,very small.In just one grain of salt are held millions of atoms. Atoms are very important.The way one object acts depends on what

  8. X-Ray photoelectron spectroscopic investigation of phenosafranine adsorbed onto micro and mesoporous materials

    Indian Academy of Sciences (India)

    S Easwaramoorthi; K Ananthanarayanan; B Sreedhar; P Natarajan

    2009-09-01

    The phenosafranine adsorbed onto the micro and mesoporous materials prepared by ion exchange method and interaction of the dye with host materials were studied by X-ray photoelectron spectroscopy to elucidate the influence of the host matrix on the binding energy of N 1s orbital. Core level N 1s X-ray photoelectron spectroscopy reveals the interaction between the dye and the solid surface through the hydrogen bonding between the hydrogen atoms of primary amino groups in dye molecule and the oxygen atom of surface hydroxyl groups. The strength of the hydrogen bonding depends on the nature of the solid surface. In the dye adsorbed onto the micro and mesoporous materials the interaction between adsorbed phenosafranine and the surfaces of the porous materials are found to modify the optical spectra and the excited state dynamics of the confined phenosafranine molecules. The change in photophysical properties of phenosafranine adsorbed on to the host materials on dehydration at elevated temperatures is attributed to the modification of host surface during dehydration process.

  9. Methane formation from the reactions of hydroxyl radicals and hydrogen atoms with dimethyl sulfoxide (DMSO)

    International Nuclear Information System (INIS)

    Acidic, aqueous, deaerated solutions of pure DMSO, of DMSO-KBr and of DMSO-EtOH in completely filled glass ampoules were irradiated with a 60Co γ source. The gases formed were extracted under vacuum and analysed by gas chromatography. Argon and helium were used as carrier gases and the principal gaseous products were CH4, H2, C2H6: traces of CO2 and C2H4 were also detected. It was shown that both hydrogen atoms and hydroxyl radicals react with dimethylsulfoxide in aqueous acid solution to produce methane. In both cases however only a fraction of the radicals captured gives rise to this product. Thus methane formed in the reaction of DMSO with biological systems is not unequivocal proof of the presence of OH radicals; nor is the yield of methane a direct measure of an OH yield. The rate constants k(H+DMSO)=2.6x107M-1s-1 and k(OH+DMSO)=2.1x1010M-1s-1 were determined in the presence of 5x10-1M sulfuric acid

  10. Superior visible light hydrogen evolution of Janus bilayer junctions via atomic-level charge flow steering

    Science.gov (United States)

    Li, Jie; Zhan, Guangming; Yu, Ying; Zhang, Lizhi

    2016-05-01

    Although photocatalytic hydrogen evolution (PHE) is ideal for solar-to-fuel conversion, it remains challenging to construct a highly efficient PHE system by steering the charge flow in a precise manner. Here we tackle this challenge by assembling 1T MoS2 monolayers selectively and chemically onto (Bi12O17) end-faces of Bi12O17Cl2 monolayers to craft two-dimensional (2D) Janus (Cl2)-(Bi12O17)-(MoS2) bilayer junctions, a new 2D motif different from van der Waals heterostructure. Electrons and holes from visible light-irradiated Bi12O17Cl2 are directionally separated by the internal electric field to (Bi12O17) and (Cl2) end-faces, respectively. The separated electrons can further migrate to MoS2 via Bi-S bonds formed between (Bi12O17) and MoS2 monolayers. This atomic-level directional charge separation endows the Janus bilayers with ultralong carrier lifetime of 3,446 ns and hence a superior visible-light PHE rate of 33 mmol h-1 g-1. Our delineated Janus bilayer junctions on the basis of the oriented assembly of monolayers presents a new design concept to effectively steer the charge flow for PHE.

  11. Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms

    Science.gov (United States)

    Song, Lei; Balakrishnan, N.; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C.

    2015-05-01

    We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 - 30 to v' = 0, j' are calculated using the close coupling method for collision energies between 0.1 and 15 000 cm-1 based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ≥ 3 to v' = 0, j' are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H-CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H-CO collisions in astrophysical models.

  12. Spatial and Kinematical Lopsidedness of Atomic Hydrogen in the Ursa Major Group of Galaxies

    CERN Document Server

    Angiras, R A; Dwarakanath, K S; Verheijen, M A W

    2007-01-01

    We have carried out the harmonic analysis of the atomic hydrogen (HI) surface density maps and the velocity fields for 11 galaxies belonging to the Ursa Major group, over a radial range of 4-6 disc scalelengths in each galaxy. This analysis gives the radial variation of spatial lopsidedness, quantified by the Fourier amplitude A$_1$ of the m=1 component normalised to the average value. The kinematical analysis gives a value for the elongation of the potential to be $\\sim 10 % $. The mean amplitude of spatial lopsidedness is found to be $\\sim 0.14$ in the inner disc, similar to the field galaxies, and is smaller by a factor of $\\sim 2$ compared to the Eridanus group galaxies. It is also shown that the the average value of A$_1$ does not increase with the Hubble type, contrary to what is seen in field galaxies. We argue that the physical origin of lopsidedness in the Ursa Major group of galaxies is tidal interactions, albeit weaker and less frequent than in Eridanus. Thus systematic studies of lopsidedness in g...

  13. Massive stars formed in atomic hydrogen reservoirs: H i observations of gamma-ray burst host galaxies

    DEFF Research Database (Denmark)

    Michałowski, M. J.; Gentile, G.; Hjorth, J.;

    2015-01-01

    Long gamma-ray bursts (GRBs), among the most energetic events in the Universe, are explosions of massive and short-lived stars, so they pinpoint locations of recent star formation. However, several GRB host galaxies have recently been found to be deficient in molecular gas (H2), believed......, implying high levels of atomic hydrogen (HI), which suggests that the connection between atomic gas and star formation is stronger than previously thought. In this case, it is possible that star formation is directly fuelled by atomic gas (or that the H1-to-H2 conversion is very efficient, which rapidly...... exhaust molecular gas), as has been theoretically shown to be possible. This can happen in low-metallicity gas near the onset of star formation because cooling of gas (necessary for star formation) is faster than the H1-to-H2 conversion. Indeed, large atomic gas reservoirs, together with low molecular gas...

  14. The inter-adsorbate interaction mediated by Shockley-type surface state electrons and dipole moment: Cs and Ba atoms absorbed on Ag (1 1 1) films

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Shuyuan [College of Physical Science and Technology, Sichuan University, Chengdu 610065 (China); Zhang, Hong, E-mail: hongzhang@scu.edu.cn [College of Physical Science and Technology, Sichuan University, Chengdu 610065 (China); Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Miyamoto, Yoshiyuki [Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba 305-8568 (Japan)

    2014-01-15

    Through first-principles investigation, we display the formation process of Shockley-type surface states which emerges on silver thin films along Ag (1 1 1) orientation with increasing thicknesses from 6 to 21 layers. We look at the surface state band for various adatoms adsorbed on 6, 12, 18 layers strained Ag (1 1 1) films with different coverage, and discuss the long range interaction mediated by surface state electrons. We discovered that film's thickness can modulate the surface state mediated interaction drastically, but the dipole–dipole repulsive interaction is not affected by slab thickness. This factor had never been discussed in detail. Therefore, adatoms adsorbed on thin films have strong attractive interaction which leads to small adsorption separation and the tendency of island formation. For different coverage or different adsorbate types, both surface states and dipole moment are modulated. The three factors, film's thickness, adsorbate coverage and adatoms types, could help us learn more about the interactions between adatoms and exploit advanced ways to control surface geometry structures of self-assembly.

  15. Bibliography of electron and photon cross sections with atoms and molecules published in the 20th century. Hydrogen halide molecules

    International Nuclear Information System (INIS)

    Bibliographies of original and review reports of experiments or theories of electron and photon cross sections and also electron swarm data are presented for atomic or molecular species with specified targets. These works covered 17 atoms and 51 molecules. The present bibliography is only for hydrogen halide molecules (HF, HCL, HBr, HI). About 330 (HF), 420 (HCl) 220 (HBr) and 150 (HI) papers were compiled respectively. Comprehensive author indexes for each molecule are included. The bibliography covers the period 1903 through 2000 for HF-HI. Finally, author's comments for HBr electron collision cross sections are given. (author)

  16. Resonant multiphoton ionization of the 1s state of a hydrogen atom in a strong laser field

    International Nuclear Information System (INIS)

    The process of resonant multiphoton ionization of hydrogen atom in the main state 1s is studied by the method of direct numerical integration of the Schroedinger nonstationary equation for quantum system in the field of an electromagnetic wave. A nonmonotonous dependence of photoionization probability on radiation intensity is found. It is ascertained that multiphoton resonances between the main and one of excited (Rydberg) atomic states induced by laser radiation field correspond to ionization minima. It is shown that ionization suppression occurs as a result of the Rydberg states restructuring in a strong field, being accompanied by effective Raman transitions binding the totality of the close-by Rydberg states

  17. Bibliography of electron and photon cross sections with atoms and molecules published in the 20th century. Hydrogen molecules

    International Nuclear Information System (INIS)

    Bibliographies of original and review reports of experiments or theories of electron and photon cross sections and also electron swarm data are presented for atomic or molecular species with specified targets. These works covered 17 atoms and 51 molecules. The present bibliography is only for hydrogen molecules (H2, HD, HT, D2, DT, T2). About 2200 papers were compiled. A comprehensive author index is included. The bibliography covers the period 1901 through 2000 for H2. Finally, author's comments for H2 electron collision cross sections are given. (author)

  18. Temperature dependence of the formation rates of hydrogen-helium mesic molecules in collisions of slow hydrogen atoms with helium

    International Nuclear Information System (INIS)

    Muon transfer from the ground state of the muonic hydrogen to helium is of special interest, since it is connected with problem of muon-catalyzed fusion in the deuterium-tritium mixture. The muon transfer rates are calculated at low energy collisions of hydrogen isotopes with helium isotopes. The calculations are carried out in an improved adiabatic approximation. The particular attention is given to the construction of the effective potential. The level energies ε00 and ε10 of the hydrogen-helium muonic molecules are presented. For collision energies ε ≤ 0.1 eV rate of the direct muon transfer does not depend on energy and amounts to λ pHe ∼ 0.06 x 108 s-1. The theoretical results λ obtained by various temperatures are compared with the available experimental data

  19. The closed-orbit and the photoabsorption spectra of the Rydberg hydrogen atom between two parallel metallic surfaces

    Institute of Scientific and Technical Information of China (English)

    Wang De-Hua

    2007-01-01

    Using the closed orbit theory,we study the classical motion and calculate the photoabsorption spectra of Rydberg hydrogen atom between two parallel metallic surfaces.The results show that the metallic surfaces have a significant effect on the photoabsorption process.When the distances between the hydrogen atom and the two metallic surfaces are close to a critical value dc,the number of the closed orbits is the greatest.When the distance larger or smaller than dc,the number of the closed orbits decreases and the absorption spectra are shown to exhibit a damping oscillation.This work is an interesting new application of closed-orbit theory and is of potential experimental interest.

  20. Analysis of mechanism of carbon removal from GaAs(1 0 0) surface by atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Tomkiewicz, P. [Department of Electron Technology, Silesian University of Technology, 44-100 Gliwice (Poland)], E-mail: ptomkiewicz@polsl.pl; Winkler, A. [Institute of Solid State Physics, Graz University of Technology, A-8010 Graz (Austria); Krzywiecki, M. [Department of Electron Technology, Silesian University of Technology, 44-100 Gliwice (Poland); Chasse, Th. [Institute of Physical and Theoretical Chemistry, University Tuebingen, 72076 Tuebingen (Germany); Szuber, J. [Department of Electron Technology, Silesian University of Technology, 44-100 Gliwice (Poland)

    2008-10-15

    Etching of carbon contaminations from the GaAs(1 0 0) surface by irradiating with atomic hydrogen, which is one of the key reactions to promote high-quality thin films growth by molecular beam epitaxy (MBE), has been investigated by mass spectrometry (MS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). It is shown that during the cleaning process at room temperature a total reduction of the Auger carbon signal, accompanied by desorption of methane as major reaction product, can be observed. The reaction pathways as well as the processes responsible for the observed carbon removal are discussed in detail to give a support for etching and growth quality enhancement not only in thin films epitaxy but in all atomic hydrogen promoted gas-phase III-V semiconductor processes.

  1. Hydrogen atom in a quantum plasma environment under the influence of Aharonov-Bohm flux and electric and magnetic fields

    CERN Document Server

    Falaye, Babatunde James; Silva-Ortigoza, Ramón; Dong, Shi-Hai

    2016-01-01

    This study presents the confinement influences of Aharonov-Bohm-flux (AB-flux), electric and magnetic fields directed along $z$-axis and encircled by quantum plasmas, on the hydrogen atom. The all-inclusive effects result to a strongly attractive system while the localizations of quantum levels change and the eigenvalues decrease. We find that, the combined effect of the fields is stronger than solitary effect and consequently, there is a substantial shift in the bound state energy of the system. We also find that to perpetuate a low-energy medium for hydrogen atom in quantum plasmas, strong electric field and weak magnetic field are required, where AB-flux field can be used as a regulator. The application of perturbation technique utilized in this paper is not restricted to plasma physics, it can also be applied in molecular physics.

  2. Resonant charge transfer of hydrogen Rydberg atoms incident at a Cu(100) projected band-gap surface

    CERN Document Server

    Gibbard, J A; Kohlhoff, M; Rennick, C J; So, E; Ford, M; Softley, T P

    2015-01-01

    The charge transfer (ionization) of hydrogen Rydberg atoms (principal quantum number $n=25-34$) incident at a Cu(100) surface is investigated. Unlike fully metallic surfaces, where the Rydberg electron energy is degenerate with the conduction band of the metal, the Cu(100) surface has a projected bandgap at these energies, and only discrete image states are available through which charge transfer can take place. Resonant enhancement of charge transfer is observed at hydrogen principal quantum numbers for which the Rydberg energy matches the energy of one of the image states. The integrated surface ionization signals show clear periodicity as the energies of states with increasing $n$ come in and out of resonance with the image states. The velocity dependence of the surface ionization dynamics is also investigated. Decreased velocity of the incident H atom leads to a greater mean distance of ionization and a lower field required to extract the ion. The surface-ionization profiles (signal versus applied field) ...

  3. Hydrogen atom in a quantum plasma environment under the influence of Aharonov-Bohm flux and electric and magnetic fields

    Science.gov (United States)

    Falaye, Babatunde James; Sun, Guo-Hua; Silva-Ortigoza, Ramón; Dong, Shi-Hai

    2016-05-01

    This study presents the confinement influences of Aharonov-Bohm (AB) flux and electric and magnetic fields directed along the z axis and encircled by quantum plasmas on the hydrogen atom. The all-inclusive effects result in a strongly attractive system while the localizations of quantum levels change and the eigenvalues decrease. We find that the combined effect of the fields is stronger than a solitary effect and consequently there is a substantial shift in the bound state energy of the system. We also find that to perpetuate a low-energy medium for the hydrogen atom in quantum plasmas, a strong electric field and weak magnetic field are required, whereas the AB flux field can be used as a regulator. The application of the perturbation technique utilized in this paper is not restricted to plasma physics; it can also be applied in molecular physics.

  4. Angular correlation measurements for electron impact excitation of the 32Psub(j) states of atomic hydrogen

    International Nuclear Information System (INIS)

    Angular correlation measurements have been made of the Lsub(β) fluorescence arising from the excitation of the 32Psub(j) states of atomic hydrogen detected in coincidence with electrons scattered with n = 3 energy loss. Data are presented for incident energies of 54.4 and 100 eV and electron scattering angles 20 and 25 deg, and compared with the predictions of the first Born approximation. (author)

  5. Angular correlation measurements for electron impact excitation of the 3/sup 2/P/sub j/ states of atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Chwirot, S.; Slevin, J.

    1987-11-28

    Angular correlation measurements have been made of the L/sub ..beta../ fluorescence arising from the excitation of the 3/sup 2/P/sub j/ states of atomic hydrogen detected in coincidence with electrons scattered with n = 3 energy loss. Data are presented for incident energies of 54.4 and 100 eV and electron scattering angles 20 and 25 deg, and compared with the predictions of the first Born approximation.

  6. Relativistic theory of the above-threshold multiphoton ionization of hydrogen-like atoms in the ultrastrong laser fields

    OpenAIRE

    Avetissian, H. K.; Markossian, A. G.; Mkrtchian, G. F.

    1999-01-01

    The relativistic theory of above-threshold ionization (ATI) of hydrogen-like atoms in ultrastrong radiation fields, taking into account the photoelectron induced rescattering in the continuum spectrum is developed. It is shown that the contribution of the latter in the multiphoton ionization probability even in the Born approximation by Coulomb field is of the order of ATI probability in the scope of Keldysh-Faisal-Reiss ansatz.

  7. Measuring laser carrier-envelope phase effects in the noble gases with an atomic hydrogen calibration standard

    CERN Document Server

    Khurmi, Champak; U, Satya Sainadh; Ivanov, I A; Kheifets, A S; Tong, X M; Litvinyuk, I V; Sang, R T; Kielpinski, D

    2016-01-01

    We present accurate measurements of carrier-envelope phase effects on ionisation of the noble gases with few-cycle laser pulses. The experimental apparatus is calibrated by using atomic hydrogen data to remove any systematic offsets and thereby obtain accurate CEP data on other generally used noble gases such as Ar, Kr and Xe. Experimental results for H are well supported by exact TDSE theoretical simulations however significant differences are observed in case of noble gases.

  8. Lamb Shift of n = 1 and n = 2 States of Hydrogen-like Atoms, 1 ≤ Z ≤ 110

    Energy Technology Data Exchange (ETDEWEB)

    Yerokhin, V. A. [Center for Advanced Studies, Peter the Great St. Petersburg Polytechnic University, Polytekhnicheskaya 29, St. Petersburg 195251 (Russian Federation); Shabaev, V. M. [Department of Physics, St. Petersburg State University, Ulianovskaya 1, Petrodvorets, St. Petersburg 198504 (Russian Federation)

    2015-09-15

    Theoretical energy levels of the n = 1 and n = 2 states of hydrogen-like atoms with the nuclear charge numbers 1 ≤ Z ≤ 110 are tabulated. The tabulation is based on ab initio quantum electrodynamics calculations performed to all orders in the nuclear binding strength parameter Zα, where α is the fine structure constant. Theoretical errors due to various effects are critically examined and estimated.

  9. Excitation and ionization of hydrogen and helium atoms by femtosecond laser pulses: theoretical approach by Coulomb-Volkov states

    International Nuclear Information System (INIS)

    We present a theoretical approach using Coulomb-Volkov states that appears useful for the study of atomic multi-photonic processes induced by intense XUV femtosecond laser pulses. It predicts hydrogen ionization spectra when it is irradiated by laser pulses in perturbations conditions. Three ways have been investigated. Extension to strong fields when ℎω > Ip: it requires to include the hydrogen ground state population, introducing it in standard Coulomb-Volkov amplitude leads to saturated multi-photonic ionization. Extension to multi-photonic transitions with ℎω p: new quantum paths are open by the possibility to excite the lower hydrogen bound states. Multiphoton excitation of these states is investigated using a Coulomb-Volkov approach. Extension to helium: two-photon double ionization study shows the influence of electronic correlations in both ground and final state. Huge quantity of information such as angular and energetic distributions as well as total cross sections is available. (author)

  10. Wave-function Visualization of Core-induced Interaction of Non-hydrogenic Rydberg Atom in Electric Field

    CERN Document Server

    Gao, W; Cheng, H; Zhang, S S; Liu, H P

    2015-01-01

    We have investigated the wave-function feature of Rydberg sodium in a uniform electric field and found that the core-induced interaction of non-hydrogenic atom in electric field can be directly visualized in the wave-function. As is well known, the hydrogen atom in electric field can be separated in parabolic coordinates (\\eta, \\xi), whose eigen-function can show a clear pattern towards negative and positive directions corresponding to the so-called red and blue states without ambiguity, respectively. It can be served as a complete orthogonal basis set to study the core-induced interaction of non-hydrogenic atom in electric field. Owing to complete different patterns of the probability distribution for red and blue states, the interaction can be visualized in the wave-function directly via superposition. Moreover, the constructive and destructive interferences between red and blue states are also observed in the wave-function, explicitly explaining the experimental measurement for the spectral oscillator stre...

  11. Novel atmospheric pressure plasma device releasing atomic hydrogen: reduction of microbial-contaminants and OH radicals in the air

    Science.gov (United States)

    Nojima, Hideo; Park, Rae-Eun; Kwon, Jun-Hyoun; Suh, Inseon; Jeon, Junsang; Ha, Eunju; On, Hyeon-Ki; Kim, Hye-Ryung; Choi, Kyoung Hui; Lee, Kwang-Hee; Seong, Baik-Lin; Jung, Hoon; Kang, Shin Jung; Namba, Shinichi; Takiyama, Ken

    2007-01-01

    A novel atmospheric pressure plasma device releasing atomic hydrogen has been developed. This device has specific properties such as (1) deactivation of airborne microbial-contaminants, (2) neutralization of indoor OH radicals and (3) being harmless to the human body. It consists of a ceramic plate as a positive ion generation electrode and a needle-shaped electrode as an electron emission electrode. Release of atomic hydrogen from the device has been investigated by the spectroscopic method. Optical emission of atomic hydrogen probably due to recombination of positive ions, H+(H2O)n, generated from the ceramic plate electrode and electrons emitted from the needle-shaped electrode have been clearly observed in the He gas (including water vapour) environment. The efficacy of the device to reduce airborne concentrations of influenza virus, bacteria, mould fungi and allergens has been evaluated. 99.6% of airborne influenza virus has been deactivated with the operation of the device compared with the control test in a 1 m3 chamber after 60 min. The neutralization of the OH radical has been investigated by spectroscopic and biological methods. A remarkable reduction of the OH radical in the air by operation of the device has been observed by laser-induced fluorescence spectroscopy. The cell protection effects of the device against OH radicals in the air have been observed. Furthermore, the side effects have been checked by animal experiments. The harmlessness of the device has been confirmed.

  12. Chemical Reactivity Dynamics and Quantum Chaos in Highly Excited Hydrogen Atoms in an External Field: A Quantum Potential Approach

    Directory of Open Access Journals (Sweden)

    B. Maiti

    2002-04-01

    Full Text Available Abstract: Dynamical behavior of chemical reactivity indices like electronegativity, hardness, polarizability, electrophilicity and nucleophilicity indices is studied within a quantum fluid density functional framework for the interactions of a hydrogen atom in its ground electronic state (n = 1 and an excited electronic state (n = 20 with monochromatic and bichromatic laser pulses. Time dependent analogues of various electronic structure principles like the principles of electronegativity equalization, maximum hardness, minimum polarizability and maximum entropy have been found to be operative. Insights into the variation of intensities of the generated higher order harmonics on the color of the external laser field are obtained. The quantum signature of chaos in hydrogen atom has been studied using a quantum theory of motion and quantum fluid dynamics. A hydrogen atom in the electronic ground state (n = 1 and in an excited electronic state ( n = 20 behaves differently when placed in external oscillating monochromatic and bichromatic electric fields. Temporal evolutions of Shannon entropy, quantum Lyapunov exponent and Kolmogorov – Sinai entropy defined in terms of the distance between two initially close Bohmian trajectories for these two cases show marked differences. It appears that a larger uncertainty product and a smaller hardness value signal a chaotic behavior.

  13. Thermodynamics of various F420 coenzyme models as sources of electrons, hydride ions, hydrogen atoms and protons in acetonitrile.

    Science.gov (United States)

    Xia, Ke; Shen, Guang-Bin; Zhu, Xiao-Qing

    2015-06-14

    32 F420 coenzyme models with alkylation of the three different N atoms (N1, N3 and N10) in the core structure (XFH(-)) were designed and synthesized and the thermodynamic driving forces (defined in terms of the molar enthalpy changes or the standard redox potentials in this work) of the 32 XFH(-) releasing hydride ions, hydrogen atoms and electrons, the thermodynamic driving forces of the 32 XFH˙ releasing protons and hydrogen atoms and the thermodynamic driving forces of XF(-)˙ releasing electrons in acetonitrile were determined using titration calorimetry and electrochemical methods. The effects of the methyl group at N1, N3 and N10 and a negative charge on N1 and N10 atoms on the six thermodynamic driving forces of the F420 coenzyme models and their related reaction intermediates were examined; the results show that seating arrangements of the methyl group and the negative charge have remarkably different effects on the thermodynamic properties of the F420 coenzyme models and their related reaction intermediates. The effects of the substituents at C7 and C8 on the six thermodynamic driving forces of the F420 coenzyme models and their related reaction intermediates were also examined; the results show that the substituents at C7 and C8 have good Hammett linear free energy relationships with the six thermodynamic parameters. Meanwhile, a reasonable determination of possible reactions between members of the F420 family and NADH family in vivo was given according to a thermodynamic analysis platform constructed using the elementary step thermodynamic parameter of F420 coenzyme model 2FH(-) and NADH model MNAH releasing hydride ions in acetonitrile. The information disclosed in this work can not only fill a gap in the chemical thermodynamics of F420 coenzyme models as a class of very important organic sources of electrons, hydride ions, hydrogen atoms and protons, but also strongly promote the fast development of the chemistry and applications of F420 coenzyme.

  14. On the energy spectrum of the hydrogen atom in a photon field. I

    International Nuclear Information System (INIS)

    In 1930 Weisskopf and Wigner gave an account, based on the Maxwell endash Schroedinger equations, of the natural spectral line broadening of radiation emitted by a hydrogen atom. Their calculations were based on an approximation involving certain single-photon transitions in the perturbation series for the solutions of these equations. In Part I of this series of papers the exact expressions for both the line shift and the line broadening are obtained from the Maxwell endash Dirac equations in such a way that the Weisskopf endash Wigner results appear as a second order approximation. The Maxwell endash Dirac Hamiltonian for the coupled fields is first shown to admit a complex analytic dilation in the energy variables. The Fredholm endash Born series for the resolvent is shown to converge uniformly when certain high-energy cutoff factors are included in the interaction and the photons are given a small mass. The series is then rearranged to show that the spectrum of the modified dilated Hamiltonian, which consists of a complete set of complex eigenvalues, thresholds, and branch cuts, is only a slight perturbation of the known spectrum of the dilated Hamiltonian for the uncoupled fields. The real part of the shift of each complex eigenvalue then accounts for the spectral line shift, and the complex part accounts for the associated line broadening. Finally, the implications for the scattering matrix and the various phenomena of resonance scattering are discussed. In Part II of this series these results are shown to remain valid when the cutoff factors and the photon mass are removed. copyright 1998 American Institute of Physics

  15. A theoretical study of adsorbate-adsorbate interactions on Ru(0001)

    DEFF Research Database (Denmark)

    Mortensen, Jens Jørgen; Hammer, Bjørk; Nørskov, Jens Kehlet

    1998-01-01

    Using density functional theory we study the effect of pre-adsorbed atoms on the dissociation of N(2) and the adsorption of N, N(2), and CO on Ru(0001). We have done calculations for pre-adsorbed Na, Cs, and S, and find that alkali atoms adsorbed close to a dissociating N(2) molecule will lower...... the barrier for dissociation, whereas S will increase it. The interaction with alkali atoms is mainly of an electrostatic nature. The poisoning by S is due to two kinds of repulsive interactions: a Pauli repulsion and a reduced covalent bond strength between the adsorbate and the surface d-electrons. In order...... to investigate these different interactions in more detail, we look at three different species (N atoms, and terminally bonded N(2) and CO) and use them as probes to study their interaction with two modifier atoms (Na and S). The two modifier atoms have very different properties, which allows us to decouple...

  16. Possibility of significant heating of H atoms in high-density, helicon-wave excited hydrogen plasmas

    Science.gov (United States)

    Sasaki, K.; Nakamoto, M.; Kadota, K.

    2001-10-01

    In the present work, we measured the distribution of H atom density in high-density hydrogen plasmas excited by helicon-wave discharges. The measurement was carried out in a linear machine with a uniform magnetic field of 1 kG along the cylindrical axis of the vacuum chamber. Plasmas were produced in a glass tube of 3 cm diameter by applying various rf powers to a helical antenna wound around the glass tube. The hydrogen gas pressure was 30--100 mTorr. Since the plasma was confined radially by the external magnetic field, we obtained a slender plasma column of 3 cm diameter at the center of the vacuum chamber. The distribution of the H atom density was measured by (2+1)-photon laser-induced fluorescence spectroscopy. As a result, it was found that the distribution of the H atom density had a deep dip in the high-density operation. The location of the dip corresponded to the high-density plasma column. A possible explanation for the deep dip in the plasma column is significant heating of H atoms. In general, it is known that temperatures of neutral species in low-pressure plasmas are not so far from room temperature. However, the present experimental result suggests the possibility of significant heating of neutral radicals in low-pressure, high-density plasmas. The high temperature may influence the transport and kinetics of reactive species in plasmas.

  17. ESR study of atomic hydrogen and tritium in solid T$_{2}$ and T$_{2}$:H$_{2}$ matrices below 1K

    CERN Document Server

    Sheludiakov, S; Järvinen, J; Vainio, O; Lehtonen, L; Zvezdov, D; Vasiliev, S; Lee, D M; Khmelenko, V V

    2016-01-01

    We report on the first ESR study of atomic hydrogen and tritium stabilized in a solid T$_{2}$ and T$_{2}$:H$_{2}$ matrices down to 70$\\,$mK. The concentrations of T atoms in pure T$_{2}$ approached $2\\times10^{20}$cm$^{-3}$ and record-high concentrations of H atoms $\\sim1\\times10^{20}$cm$^{-3}$ were reached in T$_{2}$:H$_{2}$ solid mixtures where a fraction of T atoms became converted into H due to the isotopic exchange reaction T+H$_2\\rightarrow$TH+H. The maximum concentrations of unpaired T and H atoms was limited by their recombination which becomes enforced by efficient atomic diffusion due to a presence of a large number of vacancies and phonons generated in the matrices by $\\beta$-particles. Recombination also appeared in an explosive manner both being stimulated and spontaneously in thick films where sample cooling was insufficient. We suggest that the main mechanism for H and T migration is physical diffusion related to tunneling or hopping to vacant sites in contrast to isotopic chemical reactions wh...

  18. Measurement of intensity-dependent rates of above-threshold ionization (ATI) of atomic hydrogen at 248 nm

    Energy Technology Data Exchange (ETDEWEB)

    Nichols, T.D.

    1991-04-01

    Measured rates of multiphoton ionization (MPI) from the ground state of atomic hydrogen by a linearly polarized, subpicosecond KrF laser pulse at 248 nm wavelength are compared to predictions of lowest-order perturbation theory, Floquet theory, and Keldysh-Faisal-Reiss (KFR) theory with and without Coulomb correction for peak irradiance of 3 {times} 10{sup 12}W/cm{sup 2} to 2 {times} 10{sup 14}W/cm{sup 2}. The Coulomb-corrected Keldysh model falls closest to the measured rates, the others being much higher or much lower. At 5 {times} 10{sup 13}W/cm{sup 2}, the number of ATI electrons decreased by a factor of approximately 40 with each additional photon absorbed. ATI of the molecular hydrogen background and of atoms from photodissociation of the molecules were also observed. The experiment employed a crossed-beam technique at ultrahigh vacuum with an rf-discharge atomic hydrogen source and a magnetic-bottle type electron time-of-flight spectrometer to count the electrons in the different ATI channels separately. The apparatus was calibrated to allow comparison of absolute as well as relative ionization rates to the theoretical predictions. This calibration involved measuring the distribution of irradiance in a focal volume that moved randomly and changed its size from time to time. A data collection system under computer control divided the time-of-flight spectra into bins according to the energy of each laser pulse. This is the first measurement of absolute rates of ATI in atomic hydrogen, and the first measurement of absolute test of MPI in atomic hydrogen without a large factor to account for multiple modes in the laser field. As such, the results of this work are important to the development of ATI theories, which presently differ by orders of magnitude in their prediction of the ionization rates. They are also important to recent calculations of temperatures in laser-heated plasmas, many of which incorporate KFR theory.

  19. Modelling Hydrogen Reduction and Hydrodeoxygenation of Oxygenates

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Y.; Xu, Q.; Cheah, S.

    2013-01-01

    Based on Density Functional Theory (DFT) simulations, we have studied the reduction of nickel oxide and biomass derived oxygenates (catechol, guaiacol, etc.) in hydrogen. Both the kinetic barrier and thermodynamic favorability are calculated with respect to the modeled reaction pathways. In early-stage reduction of the NiO(100) surface by hydrogen, the pull-off of the surface oxygen atom and simultaneous activation of the nearby Ni atoms coordinately dissociate the hydrogen molecules so that a water molecule can be formed, leaving an oxygen vacancy on the surface. In hydrogen reaction with oxygenates catalyzed by transition metals, hydrogenation of the aromatic carbon ring normally dominates. However, selective deoxygenation is of particular interest for practical application such as biofuel conversion. Our modeling shows that doping of the transition metal catalysts can change the orientation of oxygenates adsorbed on metal surfaces. The correlation between the selectivity of reaction and the orientation of adsorption are discussed.

  20. Distribution of Atomic Hydrogen in the Upper Atmosphere: Assessment of Absolute Densities and Variations in the light of Recent Observations

    Science.gov (United States)

    Bishop, J.

    2002-12-01

    Knowledge of atomic hydrogen densities ([H](z)) in the upper atmosphere is important both for understanding mesospheric-lower thermospheric (MLT) chemistry and for realistic modeling of geocoronal interactions with ionized populations (e.g., plasmasphere, ring current). Work culminating in the 1970's failed to achieve consistent determinations of the distribution of atomic hydrogen; because of this, the relevance of [H](z) determinations in other areas of aeronomic research has remained unacknowledged. Extensive independent sets of optical data, coupled with improved solar Lyman line series irradiances and corrections of assumptions used in the earlier data analyses, however, now enable us to resolve the older inconsistencies and pursue determination of quantities of genuine interest: thermospheric atomic hydrogen vertical fluxes, characteristics of the satellite atom component in the geocorona, etc. These data sets include: Wisconsin Hα\\ Mapper (WHAM) Fabry-Perot data from Kitt Peak Observatory, providing ~ \\ 40,000\\ spectra of geocoronal and galactic Balmer~α intensities beginning in 1997; very high resolution Fabry-Perot data from Pine Bluff Observatory (Wisconsin) of both Balmer~α\\ and Balmer~β\\ intensities and line profiles from 2000-2001; FUSE EUV measurements of Lyman line series intensities from 1999 and 2000 (excluding Lyman~α); MiniSat1/EURD EUV spectrometer measurements of Lyman line series intensities (excluding Lyman~α) from 1997 to 2001; and IMAGE/GEO Lyman~α\\ intensity data from geocoronal positions (satellite apogees ~ 7~R E). In this presentation, modeling analyses of representative data subsets will be discussed, focusing on results relevant to broader aeronomy topics.

  1. Collisions of electrons with hydrogen atoms I. Package outline and high energy code

    Science.gov (United States)

    Benda, Jakub; Houfek, Karel

    2014-11-01

    Being motivated by the applied researchers’ persisting need for accurate scattering data for the collisions of electrons with hydrogen atoms, we developed a computer package-Hex-that is designed to provide trustworthy results for all basic discrete and continuous processes within non-relativistic framework. The package consists of several computational modules that implement different methods, valid for specific energy regimes. Results of the modules are kept in a common database in the unified form of low-level scattering data (partial-wave T-matrices) and accessed by an interface program which is able to produce various derived quantities like e.g. differential and integral cross sections. This article is the first one of a series of articles that are concerned with the implementation and testing of the modules. Here we give an overview of their structure and present (a) the command-line interface program hex-db that can be also easily compiled into a derived code or used as a backend for a web-page form and (b) simple illustrative module specialized for high energies, hex-dwba, that implements distorted and plane wave Born approximation. Catalogue identifier: AETH_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AETH_v1_0.html Program obtainable from: CPC Program library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data etc.: 30367 No. of bytes in distributed program, including test data etc.: 232032 Distribution format: tar.gz Programming language: C++11 Operating system: Any system with a C++11 compiler (e.g. GCC 4.8.1; tested on OpenSUSE 13.1 and Windows 8). RAM: Test run 3 MiB. CPC Library Classification: 2.4 Electron scattering External libraries:GSL [49], FFTW3[52], SQLite3 [46]. All of the libraries are open-source and maintained. Nature of problem: Extraction of derived (observable) quantities from partial

  2. Hydrogen-induced mitigation of O on Ru(1010): a density-functional study.

    Science.gov (United States)

    Yakovkin, I N

    2009-07-21

    The reaction of hydrogen with oxygen adsorbed on an Ru(1010) surface has been studied by density-functional calculations and kinetic Monte Carlo simulations. In agreement with experiment, it has been found that molecular hydrogen does not react with adsorbed O. In contrast, the hydrogenation of oxygen by an atomic H beam occurs spontaneously and results in the formation of adsorbed OH molecules. Subsequent impinging H-atoms can either initiate the formation of water, which readily desorbs at room temperature thus removing the O from the surface, or lead to formation and desorption of H2. It is the latter channel that hinders, at 300 K, a complete removal of O from Ru capping layers on Si/Mo mirrors for extreme ultraviolet radiation. The estimated height of the barrier for the Langmuir-Hinshelwood reaction between adsorbed H and OH, 0.92 eV, and related position of the H2O peak in model desorption spectra (approximately 320 K) are consistent with recent experiments. The H2 desorption peak appears at higher temperature, approximately 350 K, so that in the range from 320 to 330 K adsorbed hydrogen atoms will react predominantly with OH. Hence, the present simulations predict that an efficient removal of the chemisorbed O from Ru capping layers can be achieved by heating the surface to 320-330 K in a molecular hydrogen atmosphere.

  3. Electrical and mechanical controlling of the kinetic and magnetic properties of hydrogen atoms on free-standing silicene

    Science.gov (United States)

    Podsiadły-Paszkowska, Agata; Krawiec, Mariusz

    2016-07-01

    Effects of strain, charge doping and external electric field on kinetic and magnetic properties of hydrogen atoms on a free-standing silicene layer are investigated by first-principles density functional theory. It was found that the charge doping and strain are the most effective ways of changing the hydrogen-silicene binding energy, but they can only raise its value. The perpendicular external electric field can also lower it albeit in a narrower range. The strain has also the strongest impact on diffusion processes, and the diffusion barrier can be modified up to 50% of its unstrained value. The adsorption of hydrogen atoms results in a locally antiferromagnetic ground state with the effective exchange constant of approximately 1 eV. The system can easily be driven into a nonmagnetic phase by the charge doping and strain. The obtained results are very promising in view of the silicene functionalization and potential applications of silicene in fields of modern nanoelectronics and spintronics.

  4. Determination of the 1s-2s two-photon excitation cross-section in atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Bickel, G.A.; McRae, G.A

    2000-07-01

    Hydrogen atoms are ablated from zirconium alloys into the gas phase by a pulsed Nd:YAG laser and photo-ionized with three photons at 243 nm via the two-photon 1s {sup 2}S{sub 1/2}-2s {sup 2}S{sub 1/2} resonant transition. A determination of the effective 1s-2s two-photon excitation cross-section is necessary to quantify the hydrogen atom density in the ablation plume. A measurement of the ion signal vs photo-ionization beam energy is fitted to an expression derived from the rate equations. The temporal and spatial properties of the photo-ionization laser beam, transit of the H atoms through the beam, and detector geometry are taken into account. The effective two-photon cross-section for this experimental configuration, derived with the rate equation formalism, is 3.3 {+-} 0.8 X 10{sup -28} cm{sup 4} W{sup -1}. This compares well with the ab initio prediction of 5 {+-} 1 X 10{sup -28} cm{sup 4} W{sup -1} under these experimental conditions. (author)

  5. Absolute Doubly Differential Cross Sections for Ejection of Electrons in - and Five-Body Collisions of 20 TO 114-KEV Protons on Atomic and Molecular Hydrogen.

    Science.gov (United States)

    Kerby, George W., III

    A crossed-beam experiment was performed to detect ejected electrons from ground-state atomic and molecular hydrogen after collisions with 20- to 114-keV protons. Because a pure atomic hydrogen target is not readily attainable, a method has been devised which yields atomic to molecular hydrogen doubly differential cross section (DDCS) ratios. Since the molecular hydrogen DDCS's were independently measured, the atomic cross sections could be directly calculated. Absolute cross sections differential in electron energy and angle were measured for electron energies ranging from 1.5 to 400 eV and scattering angles from 15^circ to 165^circ with respect to the fast beam. Electrons and ions were energy analyzed by an electrostatic hemispherical analyzer, which has an energy resolution of 5% and is rotatable in the scattering plane about the collision center. Atomic hydrogen is produced by a radio-frequency discharge of the type devised by J. Slevin. Hydrogen gas effuses from a 1 mm diameter nozzle in a nearly cos theta distribution. The projectile beam intersects the thermal gas targets 4 mm below the tip of the nozzle. Dissociation fractions of 74% and atomic hydrogen densities of 7 times 10 ^{11} cm^ {-3} were typical. The fraction of dissociated hydrogen was measured by detecting the reduced 9-eV ion signal from the molecular target when the RF is on. This characteristic ion signal originates from the coulomb breakup of the molecule and dissociative channels of excited H _sp{2}{+}. An auxiliary experiment was performed to determine the target densities with the aid of a low-resolution magnetic mass spectrometer after the slow recoil ions were extracted from the collision volume by a weak electric field. Comparisons of the atomic cross sections are made with theories such as the classical-trajectory Monte Carlo (CTMC) method, the plane-wave Born approximation (PWBA) and the continuum-distorted-wave eikonal-initial-state (CDW-EIS) approximation.

  6. Repulsive van der Waals forces due to hydrogen exposure on bilayer Graphene

    OpenAIRE

    Boström, Mathias; Sernelius, Bo

    2012-01-01

    We consider the effect of atomic hydrogen exposure to a system of two undoped sheets of graphene grown near a silica surface (the first adsorbed to the surface and the second freestanding near the surface). In the absence of atomic hydrogen, the van der Waals force between the sheets is attractive at all separations, causing the sheets to come closer together. However, with the addition of atomic hydrogen between the sheets, the long-range van der Waals interaction turns repulsive at a critic...

  7. Study on the GaAs(110) surface using emitted atom spectrometry

    International Nuclear Information System (INIS)

    The facilities implemented at Bariloche for the ion scattering spectrometry is described, and recent examples of the technique application to determine the atomic structure and the composition of metallic and semiconductor surfaces, pure and with different adsorbates. The surface analysis technique using emitted atom spectrometry is discussed. The sensitivity to the GaAs(110) surface atomic relaxation is presented, and the kinetic of hydrogen adsorption by the mentioned surface is studied

  8. Hydrogen intercalation under graphene on Ir(111)

    Science.gov (United States)

    Grånäs, Elin; Gerber, Timm; Schröder, Ulrike A.; Schulte, Karina; Andersen, Jesper N.; Michely, Thomas; Knudsen, Jan

    2016-09-01

    Using high resolution X-ray photoelectron spectroscopy and scanning tunneling microscopy we study the intercalation of hydrogen under graphene/Ir(111). The hydrogen intercalated graphene is characterized by a component in C 1s that is shifted -0.10 to -0.18 eV with respect to pristine graphene and a component in Ir 4f at 60.54 eV. The position of this Ir 4f component is identical to that of the Ir(111) surface layer with hydrogen atoms adsorbed, indicating that the atomic hydrogen adsorption site on bare Ir(111) and beneath graphene is the same. Based on co-existence of fully- and non-intercalated graphene, and the inability to intercalate a closed graphene film covering the entire Ir(111) surface, we conclude that hydrogen dissociatively adsorbs at bare Ir(111) patches, and subsequently diffuses rapidly under graphene. A likely entry point for the intercalating hydrogen atoms is identified to be where graphene crosses an underlying Ir(111) step.

  9. Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111)

    Science.gov (United States)

    Mahapatra, Mausumi; Burkholder, Luke; Garvey, Michael; Bai, Yun; Saldin, Dilano K.; Tysoe, Wilfred T.

    2016-08-01

    Unmodified racemic sites on heterogeneous chiral catalysts reduce their overall enantioselectivity, but this effect is mitigated in the Orito reaction (methyl pyruvate (MP) hydrogenation to methyl lactate) by an increased hydrogenation reactivity. Here, this effect is explored on a R-1-(1-naphthyl)ethylamine (NEA)-modified Pd(111) model catalyst where temperature-programmed desorption experiments reveal that NEA accelerates the rates of both MP hydrogenation and H/D exchange. NEA+MP docking complexes are imaged using scanning tunnelling microscopy supplemented by density functional theory calculations to allow the most stable docking complexes to be identified. The results show that diastereomeric interactions between NEA and MP occur predominantly by binding of the C=C of the enol tautomer of MP to the surface, while simultaneously optimizing C=O....H2N hydrogen-bonding interactions. The combination of chiral-NEA driven diastereomeric docking with a tautomeric preference enhances the hydrogenation activity since C=C bonds hydrogenate more easily than C=O bonds thus providing a rationale for the catalytic observations.

  10. Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111).

    Science.gov (United States)

    Mahapatra, Mausumi; Burkholder, Luke; Garvey, Michael; Bai, Yun; Saldin, Dilano K; Tysoe, Wilfred T

    2016-01-01

    Unmodified racemic sites on heterogeneous chiral catalysts reduce their overall enantioselectivity, but this effect is mitigated in the Orito reaction (methyl pyruvate (MP) hydrogenation to methyl lactate) by an increased hydrogenation reactivity. Here, this effect is explored on a R-1-(1-naphthyl)ethylamine (NEA)-modified Pd(111) model catalyst where temperature-programmed desorption experiments reveal that NEA accelerates the rates of both MP hydrogenation and H/D exchange. NEA+MP docking complexes are imaged using scanning tunnelling microscopy supplemented by density functional theory calculations to allow the most stable docking complexes to be identified. The results show that diastereomeric interactions between NEA and MP occur predominantly by binding of the C=C of the enol tautomer of MP to the surface, while simultaneously optimizing C=O····H2N hydrogen-bonding interactions. The combination of chiral-NEA driven diastereomeric docking with a tautomeric preference enhances the hydrogenation activity since C=C bonds hydrogenate more easily than C=O bonds thus providing a rationale for the catalytic observations. PMID:27488075

  11. Investigation of hydrogen atom addition to vinyl monomers by time resolved ESR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Beckert, D.; Mehler, K.

    1983-07-01

    By means of time resolved ESR spectroscopy in the microsecond time scale the H atom addition to different vinyl monomers was investigated. The H atoms produced by pulse radiolysis of aqueous solutions show a strong recombination CIDEP effect which also allows the recombination rate constant of H atoms to be determined. By analysis of ESR time profiles with the modified Bloch equations the relaxation times T/sub 1/, T/sub 2/, the polarization factors and the chemical rate constants with scavengers were obtained. Besides the H atom addition rate constants to different vinyl monomers the structure of the monomer radical was determined for acrylic acid.

  12. Atomic structure of the hydrogen saturated a-planes of 4H-SiC

    International Nuclear Information System (INIS)

    Full text: We have investigated the hydrogenation of the non-polar 4H-SiC(112-bar0) and (11-bar00) surfaces. Surface hydrogenation was carried out by thermal treatment in ultra-pure hydrogen. The surfaces were characterized by low-energy electron diffraction (LEED), surface sensitive photoelectron spectroscopy using synchrotron radiation (SXPS) and Fourier-transform infrared absorption spectroscopy (FTIR) in attenuated total reflection mode (ATR). The hydrogen saturated surfaces exhibit a (1x1) periodicity and are stoichiometric. C1s core level spectra taken using synchrotron radiation show a hydrogen induced chemically shifted (0.42 eV) surface component in good agreement with 6H-SiC(0001-bar)-(lxl):H surface indicating the presence of Si3C-H entities at the surface. Corresponding Si2p spectra indicate a chemically shifted surface component due to hydrogen-silicon bonds. On 4H-SiC(11-bar00) C-3Si-H entities were also dentified by absorption bands due to Si-H stretch modes. Structural models for the hydrogen saturated a-planes of 4H-SiC are derived from the spectroscopic observations

  13. Algebraic tools for dealing with the atomic shell model. I. Wavefunctions and integrals for hydrogen-like ions

    Science.gov (United States)

    Surzhykov, Andrey; Koval, Peter; Fritzsche, Stephan

    2005-01-01

    Today, the 'hydrogen atom model' is known to play its role not only in teaching the basic elements of quantum mechanics but also for building up effective theories in atomic and molecular physics, quantum optics, plasma physics, or even in the design of semiconductor devices. Therefore, the analytical as well as numerical solutions of the hydrogen-like ions are frequently required both, for analyzing experimental data and for carrying out quite advanced theoretical studies. In order to support a fast and consistent access to these (Coulomb-field) solutions, here we present the DIRAC program which has been developed originally for studying the properties and dynamical behavior of the (hydrogen-like) ions. In the present version, a set of MAPLE procedures is provided for the Coulomb wave and Green's functions by applying the (wave) equations from both, the nonrelativistic and relativistic theory. Apart from the interactive access to these functions, moreover, a number of radial integrals are also implemented in the DIRAC program which may help the user to construct transition amplitudes and cross sections as they occur frequently in the theory of ion-atom and ion-photon collisions. Program summaryTitle of program:DIRAC Catalogue number: ADUQ Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADUQ Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: None Computer for which the program is designed and has been tested: All computers with a license of the computer algebra package MAPLE [1] Program language used: Maple 8 and 9 No. of lines in distributed program, including test data, etc.:2186 No. of bytes in distributed program, including test data, etc.: 162 591 Distribution format: tar gzip file CPC Program Library subprograms required: None Nature of the physical problem: Analytical solutions of the hydrogen atom are widely used in very different fields of physics [2,3]. Despite of the rather simple structure

  14. The Synergic Effect of Atomic Hydrogen Adsorption and Catalyst Spreading on Ge Nanowire Growth Orientation and Kinking.

    Science.gov (United States)

    Kolíbal, Miroslav; Pejchal, Tomáš; Vystavěl, Tomáš; Šikola, Tomáš

    2016-08-10

    Hydride precursors are commonly used for semiconductor nanowire growth from the vapor phase and hydrogen is quite often used as a carrier gas. Here, we used in situ scanning electron microscopy and spatially resolved Auger spectroscopy to reveal the essential role of atomic hydrogen in determining the growth direction of Ge nanowires with an Au catalyst. With hydrogen passivating nanowire sidewalls the formation of inclined facets is suppressed, which stabilizes the growth in the ⟨111⟩ direction. By contrast, without hydrogen gold diffuses out of the catalyst and decorates the nanowire sidewalls, which strongly affects the surface free energy of the system and results in the ⟨110⟩ oriented growth. The experiments with intentional nanowire kinking reveal the existence of an energetic barrier, which originates from the kinetic force needed to drive the droplet out of its optimum configuration on top of a nanowire. Our results stress the role of the catalyst material and surface chemistry in determining the nanowire growth direction and provide additional insights into a kinking mechanism, thus allowing to inhibit or to intentionally initiate spontaneous kinking. PMID:27458789

  15. Investigating the effect of electric field on ionization cross sections in antiproton–hydrogen/deuterium atoms collisions

    International Nuclear Information System (INIS)

    The Classical Trajectory Monte Carlo (CTMC) method has been used to investigate the effects of aligned electric field on the ionization cross sections in antiproton and hydrogen atoms collisions. The cross sections for the ionization of hydrogen/deuterium collision with antiproton in the energy range 10–500 keV/amu have been calculated and compared with the available experiment and theoretical results. The ionization cross sections are in reasonable agreement with the recently reported experimental and theoretical results. Isotope effect in the ionization cross section is reported to be negligible. The effects of the external electric field are seen to be quite prominent. Differential cross sections for ionization at the scattering angle up to 0.1° are also reported in this paper.

  16. CHEMISORPTIONS OF ATOMIC OXYGEN AND ITS REPLACEMENT BY HYDROGEN ON THE DIAMOND (100) SURFACE STUDIED BY FIRST PRINCIPLES

    OpenAIRE

    Wang, Z. G.; X. T. ZU; J. L. NIE; H. Y. XIAO

    2006-01-01

    The initial oxidation process of a clean diamond (100) surface was studied by first-principles calculations. The O-bridge with C–O–C bond chemisorption, O-on-dimer chemisorption with epoxy structure, and O-on-top chemisorption with C=O bond structure are found to be stable on the diamond (100) surfaces. The epoxy structure is more stable than the O-bridge structure. The calculation also shows that the oxygen atom can be replaced by hydrogen in the oxidized diamond (100) surface.

  17. Theoretical and kinetic study of the hydrogen atom abstraction reactions of unsaturated C6 methyl esters with hydroxyl radical

    Science.gov (United States)

    Wang, Quan-De; Ni, Zhong-Hai

    2016-04-01

    This work reports a systematic ab initio and chemical kinetic study of the rate constants for hydrogen atom abstraction reactions by hydroxyl radical (OH) on typical isomers of unsaturated C6 methyl esters at the CBS/QB3 level of theory. The high-pressure limit rate constants at different reaction sites for all the methyl esters in the temperature range from 500 to 2000 K are calculated via transition-state theory with the Wigner method for quantum tunneling effect and fitted to the modified three parameters Arrhenius expression using least-squares regression. Further, a branching ratio analysis for each reaction site has been performed.

  18. Ac Stark splitting in multiphoton excitation of atomic hydrogen in flames: Abnormal peak asymmetry due to pressure broadening

    International Nuclear Information System (INIS)

    A theory of ac Stark (or Autler-Townes) splitting occurring in double optical resonances, one of which is a two-photon transition is developed. Both laser bandwidth and collisional broadening effects are included. Theoretical results are in excellent agreement with Goldsmith's observation of two-peaked structures in the multiphoton excitation spectra of atomic hydrogen in atmospheric-pressure flames. This is believed to be the first study demonstrating that the peak asymmetry in an ac Stark doublet can be reversed due to pressure broadening

  19. Transverse momentum asymmetry of the extracted electron in field ionization of a Hydrogen Atom with angular momentum

    CERN Document Server

    Artru, Xavier

    2014-01-01

    The tunneling ionization of a hydrogen atom excited in the presence of a static electric field is investigated for the case where, before being extracted, the electron has an orbital angular momentum L perpendicular to the field E. The escaping electron has a nonzero mean transverse velocity in the direction of E cross . This asymmetry is similar to the Collins effect in the fragmentation into hadrons of a transversely polarized quark. In addition, the linear Stark effect make and oscillate in time. The degree of asymmetry is calculated at leading order in E for an initial state of maximum transverse . The conditions for the observation of this asymmetry are discussed.

  20. Intramolecular resonance-assisted hydrogen bonds: A theoretical description by means of atomic charges and charge fluxes

    Science.gov (United States)

    Baranović, Goran

    2014-01-01

    The characterization of intramolecular H-bonds in terms of atomic charges and charge fluxes (at the B3LYP/cc-pVTZ level of theory) has been extended to the case of the so called resonance-assisted (RA) H-bonds. A quadratic correlation between the charge fluxes ϕH and the molecular IR absorption coefficients E that includes the entire family of the studied systems (31 of them) containing both intra- and intermolecular hydrogen bonds (O-H⋯O/N) confirmed the critical importance of the charge fluxes on the IR intensity enhancements. Since they reflect changing of the atomic charge distribution during the normal modes of vibrations, the dynamic nature of hydrogen bonding properties has been re-emphasized. The changes of the charge flux of the hydroxyl hydrogen in an RA intramolecular H-bond are between those for “free” OH bonds and the values calculated for intermolecular H-bonds. The transition “free” → intramolecular → intermolecular is gradual and therefore the hydrogen charge flux can be considered as practically sufficient to give quantitative measure to the intuitively obvious statement that “intramolecular H-bonding is somehow in between no H-bonding situation and intermolecular H-bonding” and thus provide a quantitative and yet simple parameterization of H-bond strength. In strictly planar molecules, the difference of the sums of charges of atoms participating in the 6-membered H-bond ring ΔΣ can serve as a measure of the charge delocalization after the H-bond is formed. The electronic charge is withdrawn from the group of six atoms when the H-bond is formed in nitrophenol (ΔΣ = -0.07), while the opposite is true (ΔΣ = +0.03) for 2-hydroxy benzylidene amine. The corresponding values of the geometrical resonance parameter Δ are 0.39 and 0.37, respectively, similar to those found for 2-hydroxy acetophenone and 2-hydroxy benzaldehyde. The extent of the π-electron delocalization as measured by the resonance parameter Δ does not follow