Microplasma discharge vacuum ultraviolet photoionization source for atmospheric pressure ionization mass spectrometry.

Science.gov (United States)

Symonds, Joshua M; Gann, Reuben N; Fernández, Facundo M; Orlando, Thomas M

2014-09-01

In this paper, we demonstrate the first use of an atmospheric pressure microplasma-based vacuum ultraviolet (VUV) photoionization source in atmospheric pressure mass spectrometry applications. The device is a robust, easy-to-operate microhollow cathode discharge (MHCD) that enables generation of VUV photons from Ne and Ne/H(2) gas mixtures. Photons were detected by excitation of a microchannel plate detector and by analysis of diagnostic sample ions using a mass spectrometer. Reactive ions, charged particles, and metastables produced in the discharge were blocked from entering the ionization region by means of a lithium fluoride window, and photoionization was performed in a nitrogen-purged environment. By reducing the output pressure of the MHCD, we observed heightened production of higher-energy photons, making the photoionization source more effective. The initial performance of the MHCD VUV source has been evaluated by ionizing model analytes such as acetone, azulene, benzene, dimethylaniline, and glycine, which were introduced in solid or liquid phase. These molecules represent species with both high and low proton affinities, and ionization energies ranging from 7.12 to 9.7 eV.

Atmospheric pressure chemical ionization studies of non-polar isomeric hydrocarbons using ion mobility spectrometry and mass spectrometry with different ionization techniques

Science.gov (United States)

Borsdorf, H.; Nazarov, E. G.; Eiceman, G. A.

2002-01-01

The ionization pathways were determined for sets of isomeric non-polar hydrocarbons (structural isomers, cis/trans isomers) using ion mobility spectrometry and mass spectrometry with different techniques of atmospheric pressure chemical ionization to assess the influence of structural features on ion formation. Depending on the structural features, different ions were observed using mass spectrometry. Unsaturated hydrocarbons formed mostly [M - 1]+ and [(M - 1)2H]+ ions while mainly [M - 3]+ and [(M - 3)H2O]+ ions were found for saturated cis/trans isomers using photoionization and 63Ni ionization. These ionization methods and corona discharge ionization were used for ion mobility measurements of these compounds. Different ions were detected for compounds with different structural features. 63Ni ionization and photoionization provide comparable ions for every set of isomers. The product ions formed can be clearly attributed to the structures identified. However, differences in relative abundance of product ions were found. Although corona discharge ionization permits the most sensitive detection of non-polar hydrocarbons, the spectra detected are complex and differ from those obtained with 63Ni ionization and photoionization. c. 2002 American Society for Mass Spectrometry.

Study of photoionization and dissociative photoionization of carbon monoxide from ionization threshold to 38 eV by using synchrotron radiation

International Nuclear Information System (INIS)

Zhao, Yujie; Cao, Maoqi; Li, Yuquan; Shan, Xiaobin; Liu, Fuyi; Sheng, Liusi; Li, Li; Liu, Wanfang

2014-01-01

Highlights: • The high resolution photoionization spectrum of carbon monoxide has been investigated using tunable synchrotron radiation. • This work has investigated comprehensively almost all kinds of photo excitation processes of CO in wide photon region. • The mechanisms of photoionization and dissociative photoionization of CO have been researched in detail. - Abstract: The vacuum-ultraviolet photoionization and dissociative photoionization of carbon monoxide in a region 14–38 eV have been investigated with time-of-flight (TOF) photoionization mass spectrometry (PIMS) using tunable synchrotron radiation (SR). The adiabatic ionization energy (IE) of carbon monoxide and appearance energies (AE) for its fragment ions in different states are determined by measurements of photoionization efficiency spectra (PIES). Ab initio calculations have been performed to investigate the reaction mechanism of dissociative photoionization of carbon monoxide. On the basis of experimental and predicted theoretical results, the mechanisms of photoionization and dissociative photoionization of molecular CO are discussed, and sixteen dissociative photoionization processes are proposed. The equilibrium geometries and harmonic vibrational frequencies of CO molecule, and its parent cation were calculated by using MP2 (full) method. The differences of configurations between them are also discussed on the basis of theoretical calculations. According to our results, the experimental IE of CO molecule, and dissociation energies (E d ) of possible dissociative channels are in reasonable agreement with the calculated values of the proposed photodissociation channels

Ionization of EPA contaminants in direct and dopant-assisted atmospheric pressure photoionization and atmospheric pressure laser ionization.

Science.gov (United States)

Kauppila, Tiina J; Kersten, Hendrik; Benter, Thorsten

2015-06-01

Seventy-seven EPA priority environmental pollutants were analyzed using gas chromatography-mass spectrometry (GC-MS) equipped with an optimized atmospheric pressure photoionization (APPI) and an atmospheric pressure laser ionization (APLI) interface with and without dopants. The analyzed compounds included e.g., polycyclic aromatic hydrocarbons (PAHs), nitro compounds, halogenated compounds, aromatic compounds with phenolic, acidic, alcohol, and amino groups, phthalate and adipatic esters, and aliphatic ethers. Toluene, anisole, chlorobenzene, and acetone were tested as dopants. The widest range of analytes was ionized using direct APPI (66/77 compounds). The introduction of dopants decreased the amount of compounds ionized in APPI (e.g., 54/77 with toluene), but in many cases the ionization efficiency increased. While in direct APPI the formation of molecular ions via photoionization was the main ionization reaction, dopant-assisted (DA) APPI promoted ionization reactions, such as charge exchange and proton transfer. Direct APLI ionized a much smaller amount of compounds than APPI (41/77 compounds), showing selectivity towards compounds with low ionization energies (IEs) and long-lived resonantly excited intermediate states. DA-APLI, however, was able to ionize a higher amount of compounds (e.g. 51/77 with toluene), as the ionization took place entirely through dopant-assisted ion/molecule reactions similar to those in DA-APPI. Best ionization efficiency in APPI and APLI (both direct and DA) was obtained for PAHs and aromatics with O- and N-functionalities, whereas nitro compounds and aliphatic ethers were the most difficult to ionize. Halogenated aromatics and esters were (mainly) ionized in APPI, but not in APLI.

Generation of L sub-shell photo-ionization cross-sections for elements 18Z92 at energies .320-115.606 keV (A computer program 'LSPICS')

International Nuclear Information System (INIS)

Sharma, Ajay; Mittal, Raj

2005-01-01

L sub-shell photo-ionization cross-sections, σ Li , for elements 18Z92 at energies .320-115.606 keV have been generated from an empirical relation fitted to Scofield's L sub-shell photo-ionization cross-section values. The excitation energy E for an element is constrained by the condition that only L and higher shell vacancies are produced in the elements. The closeness of generated and existing values of Scofield's L sub-shell data recommends the use of generated values in the fields of atomic and molecular physics and for trace elemental analysis. For this purpose computer software 'LSPICS' has been developed. On personal computer LSPICS generates L sub-shell photo-ionization cross-section values in barns just by entering the atomic number of element and excitation photon energy in keV

On the photo-ionization of impurity centres in semiconductors

International Nuclear Information System (INIS)

Tomak, M.

1982-10-01

The dependence of the photo-ionization cross-section on photon energy is calculated. The impurity potential is assumed to be of the Hulthen potential type and bound state wave function is calculated variationally. The results show that, at least in some cases, the Hulthen potential may describe the impurity better than the hydrogen or delta function potentials. (author)

Optogalvanic photoionization spectroscopy

International Nuclear Information System (INIS)

Levesque, S.; Gagne, J.-M.; Babin, F.

1997-01-01

This paper presents, for the first time, a systematic study of an optogalvanic method for photoionization spectroscopy. The method is particularly attractive for refractory and complex atoms, such as lanthanides and actinides. The relevant characteristics of the hollow cathode discharges used for this study are discussed in detail, along with the experimental protocol for this spectroscopic method. The rapid optogalvanic effect, which results solely from photoionization, is also described. Finally, we present as an example of the application of this method, a table containing some of the recorded uranium photoionization lines in the 16 300-20 500 cm -1 range, along with typical samples of the uranium single-colour photoionization spectrum recorded using the rapid optogalvanic technique. A brief discussion of the sensitivity of the rapid optogalvanic effect is also presented. It appears that the rapid optogalvanic effect is very effective in the detection of highly excited levels. This technique permitted the observation of many new single-colour resonant ionization uranium lines. (Author)

Photoionization of FE3+ Ions

International Nuclear Information System (INIS)

Ovchinnikov, O.; Schlachter, F.

2003-01-01

Photoionization of Fe3+ ions was studied for the first time using synchrotron radiation from the Advanced Light Source (ALS) and the merged-beams technique. Fe3+ ions were successfully produced using ferrocene in an electron cyclotron resonance ion source (ECR). The measured yield of Fe4+ photoions as a function of photon energy revealed the presence of resonances that correspond to excitation of autoionizing states. These resonances are superimposed upon the photoion yield produced by direct photoionization, which is a smooth, slowly decreasing function of energy. The spectra for the photoionization of Fe3+ will be analyzed and compared with theory. The data collected will also serve to test models for the propagation of light through ionized matter.

The photoionization of the diffuse galactic gas

Science.gov (United States)

Mathis, J. S.

1986-01-01

In a study of the diffuse ionized gas (DIG) component of the interstellar medium, it is attempted to see if the general properties of dilute gas ionized by O stars are similar to observations and to what extent the observations of the DIG can be used to determine the nature of the ionizing radiation field at great distances above the plane of the Galaxy. It has been suggested by Reynolds (1985) that either shocks or photoionization might be responsible for the DIG. The photoionization model seems required by the observations.

Photoionization in the halo of the Galaxy

Science.gov (United States)

Bregman, Joel N.; Harrington, J. Patrick

1986-01-01

The ionizing radiation field in the halo is calculated and found to be dominated in the 13.6-45 eV range by light from O-B stars that escapes the disk, by planetary nebulae at 45-54 eV, by quasars and the Galactic soft X-ray background at 54-2000 eV, and by the extragalactic X-ray background at higher energies. Photoionization models are calculated with this radiation field incident on halo clouds of constant density for a variety of densities, for normal and depleted abundances, and with variations of the incident spectrum. For species at least triply ionized, such as Si IV, C IV, N V, and O VI, the line ratios are determined by intervening gas with the greatest volume, which is not necessarily the greatest mass component. Column densities from doubly ionized species like Si III should be greater than from triply ionized species. The role of photoionized gas in cosmic ray-supported halos and Galactic fountains is discussed. Observational tests of photoionization models are suggested.

Photo-Ionization of Noble Gases: A Demonstration of Hybrid Coupled Channels Approach

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Vinay Pramod Majety

2015-01-01

Full Text Available We present here an application of the recently developed hybrid coupled channels approach to study photo-ionization of noble gas atoms: Neon and Argon. We first compute multi-photon ionization rates and cross-sections for these inert gas atoms with our approach and compare them with reliable data available from R-matrix Floquet theory. The good agreement between coupled channels and R-matrix Floquet theory show that our method treats multi-electron systems on par with the well established R-matrix theory. We then apply the time dependent surface flux (tSURFF method with our approach to compute total and angle resolved photo-electron spectra from Argon with linearly and circularly polarized 12 nm wavelength laser fields, a typical wavelength available from Free Electron Lasers (FELs.

Photoionization by a bichromatic field: Adiabatic theory

International Nuclear Information System (INIS)

Pazdzersky, V.A.; Yurovsky, V.A.

1995-01-01

Atom photoionization by the superposition of a fundamental field and its second harmonic is considered. The finite analytical expressions for the photoionization probability are obtained using the adiabatic approximation. They demonstrate that the photoelectron angular distribution has a polar symmetry when the electrical field strength has a maximal polar asymmetry and the distribution is asymmetrical when the field is symmetrical. A strict proof of the polar symmetry of the photoionization probability in the case of the electrical field with maximal asymmetry is deduced using the Keldysh-Faisal-Reiss theories. The obtained results are in agreement with the experimental data available

Ionization techniques in capillary electrophoresis-mass spectrometry: principles, design, and application.

Science.gov (United States)

Hommerson, Paul; Khan, Amjad M; de Jong, Gerhardus J; Somsen, Govert W

2011-01-01

A major step forward in the development and application of capillary electrophoresis (CE) was its coupling to ESI-MS, first reported in 1987. More than two decades later, ESI has remained the principal ionization technique in CE-MS, but a number of other ionization techniques have also been implemented. In this review the state-of-the-art in the employment of soft ionization techniques for CE-MS is presented. First the fundamentals and general challenges of hyphenating conventional CE and microchip electrophoresis with MS are outlined. After elaborating on the characteristics and role of ESI, emphasis is put on alternative ionization techniques including sonic spray ionization (SSI), thermospray ionization (TSI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), matrix-assisted laser desorption ionization (MALDI) and continuous-flow fast atom bombardment (CF-FAB). The principle of each ionization technique is outlined and the experimental set-ups of the CE-MS couplings are described. The strengths and limitations of each ionization technique with respect to CE-MS are discussed and the applicability of the various systems is illustrated by a number of typical examples. Copyright © 2011 Wiley Periodicals, Inc.

Probing photo-ionization: experiments on positive streamers in pure gases and mixtures

International Nuclear Information System (INIS)

Nijdam, S; Van de Wetering, F M J H; Blanc, R; Van Veldhuizen, E M; Ebert, U

2010-01-01

Positive streamers are thought to propagate by photo-ionization; the parameters of photo-ionization depend on the nitrogen : oxygen ratio. Therefore we study streamers in nitrogen with 20%, 0.2% and 0.01% oxygen and in pure nitrogen as well as in pure oxygen and argon. Our new experimental set-up guarantees contamination of the pure gases to be well below 1 ppm. Streamers in oxygen are difficult to measure as they emit considerably less light in the sensitivity range of our fast ICCD camera than the other gases. Streamers in pure nitrogen and in all nitrogen-oxygen mixtures look generally similar, but become somewhat thinner and branch more with decreasing oxygen content. In pure nitrogen the streamers can branch so much that they resemble feathers. This feature is even more pronounced in pure argon, with approximately 10 2 hair tips cm -3 in the feathers at 200 mbar; this density can be interpreted as the free electron density creating avalanches towards the streamer stem. It is remarkable that the streamer velocity is essentially the same for similar voltage and pressure in all nitrogen-oxygen mixtures as well as in pure nitrogen, while the oxygen concentration and therefore the photo-ionization lengths vary by more than five orders of magnitude. Streamers in argon have essentially the same velocity as well. The physical similarity of streamers at different pressures is confirmed in all gases; the minimal diameters are smaller than in earlier measurements.

Probing photo-ionization: experiments on positive streamers in pure gases and mixtures

Energy Technology Data Exchange (ETDEWEB)

Nijdam, S; Van de Wetering, F M J H; Blanc, R; Van Veldhuizen, E M; Ebert, U, E-mail: s.nijdam@tue.n [Eindhoven University of Technology, Department Applied Physics, PO Box 513, 5600 MB Eindhoven (Netherlands)

2010-04-14

Positive streamers are thought to propagate by photo-ionization; the parameters of photo-ionization depend on the nitrogen : oxygen ratio. Therefore we study streamers in nitrogen with 20%, 0.2% and 0.01% oxygen and in pure nitrogen as well as in pure oxygen and argon. Our new experimental set-up guarantees contamination of the pure gases to be well below 1 ppm. Streamers in oxygen are difficult to measure as they emit considerably less light in the sensitivity range of our fast ICCD camera than the other gases. Streamers in pure nitrogen and in all nitrogen-oxygen mixtures look generally similar, but become somewhat thinner and branch more with decreasing oxygen content. In pure nitrogen the streamers can branch so much that they resemble feathers. This feature is even more pronounced in pure argon, with approximately 10{sup 2} hair tips cm{sup -3} in the feathers at 200 mbar; this density can be interpreted as the free electron density creating avalanches towards the streamer stem. It is remarkable that the streamer velocity is essentially the same for similar voltage and pressure in all nitrogen-oxygen mixtures as well as in pure nitrogen, while the oxygen concentration and therefore the photo-ionization lengths vary by more than five orders of magnitude. Streamers in argon have essentially the same velocity as well. The physical similarity of streamers at different pressures is confirmed in all gases; the minimal diameters are smaller than in earlier measurements.

Comparison of the sensitivity of mass spectrometry atmospheric pressure ionization techniques in the analysis of porphyrinoids.

Science.gov (United States)

Swider, Paweł; Lewtak, Jan P; Gryko, Daniel T; Danikiewicz, Witold

2013-10-01

The porphyrinoids chemistry is greatly dependent on the data obtained in mass spectrometry. For this reason, it is essential to determine the range of applicability of mass spectrometry ionization methods. In this study, the sensitivity of three different atmospheric pressure ionization techniques, electrospray ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization, was tested for several porphyrinods and their metallocomplexes. Electrospray ionization method was shown to be the best ionization technique because of its high sensitivity for derivatives of cyanocobalamin, free-base corroles and porphyrins. In the case of metallocorroles and metalloporphyrins, atmospheric pressure photoionization with dopant proved to be the most sensitive ionization method. It was also shown that for relatively acidic compounds, particularly for corroles, the negative ion mode provides better sensitivity than the positive ion mode. The results supply a lot of relevant information on the methodology of porphyrinoids analysis carried out by mass spectrometry. The information can be useful in designing future MS or liquid chromatography-MS experiments. Copyright © 2013 John Wiley & Sons, Ltd.

Density-matrix formalism for the photoion-electron entanglement in atomic photoionization

International Nuclear Information System (INIS)

Radtke, T.; Fritzsche, S.; Surzhykov, A.

2006-01-01

The density-matrix theory, based on Dirac's relativistic equation, is applied for studying the entanglement between the photoelectron and residual ion in the course of the photoionization of atoms and ions. In particular, emphasis is placed on deriving the final-state density matrix of the overall system 'photoion+electron', including interelectronic effects and the higher multipoles of the radiation field. This final-state density matrix enables one immediately to analyze the change of entanglement as a function of the energy, angle and the polarization of the incoming light. Detailed computations have been carried out for the 5s photoionization of neutral strontium, leading to a photoion in a 5s 2 S J f =1/2 level. It is found that the photoion-electron entanglement decreases significantly near the ionization threshold and that, in general, it depends on both the photon energy and angle. The possibility to extract photoion-electron pairs with a well-defined degree of entanglement may have far-reaching consequences for quantum information and elsewhere

Photoion spectroscopy of atoms using coincidence techniques

International Nuclear Information System (INIS)

Hayaishi, Tatsuji

1990-01-01

Interaction of atoms or molecules with photons causes many effects which are often obscured because of many decay paths from the event. To pick up an effect in the mixed-up ones, it is necessary to observe the decay path arising the effect alone. There is a coincidence technique in one of experimental means for the purpose of observing the decay path. In this article, two coincidence measurements are presented; a photoelectron-photoion coincidence technique and a threshold photoelectron-photoion coincidence technique. Furthermore, experimental facts of rare gases atoms obtained by the techniques are reviewed. (author)

Absolute cross sections for photoionization of Xeq+ ions (1 ⩽ q ⩽ 5) at the 3d ionization threshold

International Nuclear Information System (INIS)

Schippers, S; Ricz, S; Buhr, T; Borovik, A Jr; Hellhund, J; Holste, K; Huber, K; Schäfer, H-J; Schury, D; Klumpp, S; Mertens, K; Martins, M; Flesch, R; Ulrich, G; Rühl, E; Jahnke, T; Lower, J; Metz, D; Schmidt, L P H; Schöffler, M

2014-01-01

The photon-ion merged-beams technique has been employed at the new Photon-Ion spectrometer at PETRA III for measuring multiple photoionization of Xe q+ (q = 1–5) ions. Total ionization cross sections have been obtained on an absolute scale for the dominant ionization reactions of the type hν + Xe q+ → Xe r+ + (q − r)e − with product charge states q + 2 ⩽ r ⩽ q + 5. Prominent ionization features are observed in the photon-energy range 650–750 eV, which are associated with excitation or ionization of an inner-shell 3d electron. Single-configuration Dirac–Fock calculations agree quantitatively with the experimental cross sections for non-resonant photoabsorption, but fail to reproduce all details of the measured ionization resonance structures. (paper)

Photoionization cross-section of thallium 7 2D5/2 state at 1.06 μm radiation

International Nuclear Information System (INIS)

Ko, Kwang Hoon; Jeong, Do Young; Lim, Gwon; Kim, Jae Woo; Kim, Taek Soo; Rho, Si Pyo; Kim, Cheol Jung

2003-01-01

Thallium has two naturally occurring isotopes of T1-203 and T1-205, which have abundances of 30% and 70%, respectively. Development of the isotope separation technique of T1-203 has been attractive due to its industrial demand. T1-203 is raw material for production of T1-201 radioisotopes by proton bombardment in a cyclotron. The final product of 2 01 'T1C1 radiopharmaceuticals is widely used to diagnose heart disease. Electric field ionization has been proposed for isotope selective ionization of thallium atoms but it is not adequate to produce massive thallium ions. We report the result of infra-red (IR) photoionization experiment of thallium atoms. The measures photoionization cross-section of 7 2 D 5/2 state of atoms was at 1.06 μm radiation, which means that ionization efficiency higher than 80% can be achieved with a pulsed Nd:YAG laser of pulse energy density of about. For the accurate determination of the photoionization cross-section, calibration of the linearity of a energy meter should be performed. Density matrix equations were employed for the simulation of the photoionization process and its results were used to determine the photoionization cross-section.

Correlation between photoeletron and photoion in ultrafast multichannel photoionization of Ar

International Nuclear Information System (INIS)

Itakura, R.; Fushitani, M.; Hishikawa, A.; Sako, T.

2015-01-01

We theoretically investigate coherent dynamics of ions created through ultrafast multichannel photoionization from a viewpoint of photoelectron-photoion correlation. The model calculation on single-photon ionization of Ar reveals that the coherent hole dynamics in Ar + associated with a superposition of the spin-orbit states 2 PJ (J = 3/2 and 1/2) can be identified by monitoring only the photoion created by a Fourier-transform limited extreme ultraviolet (EUV) pulse with the fs pulse duration, while the coherence is lost by a chirped EUV pulse. It is demonstrated that by coincidence detection of the photoelectron and photoion the coherent hole dynamics can be extracted even in the case of ionization by a chirped EUV pulse with the sufficiently wide bandwidth

Interference effects at photoionization of Rydberg atoms by a strong electromagnetic field

International Nuclear Information System (INIS)

Movsesyan, A.M.; Fedorov, M.V.

1989-01-01

The photoionization of Rydberg atoms in a strong electromagnetic field is considered. Degeneration of the levels with respect to the orbital moment, their Stark splitting and the possibility of resonant interaction with levels of lower energy are taken into account. The complex quasi-energies of the system, photoelectron spectrum in the limit of an infinite duration of interaction and the time dependence of the total ionization probability are found. It is shown that a narrowing of the quasi-energy levels occurs in a strong field. Against a background of the quasi- continuum the quasi-energy spectrum consists of more or less narrow levels. In this case the photoelectron spectrum acquires a multi-peak form. With increasing field strength the height of the peaks increases, whereas their width decreases. The ionization rate decreases with increasing field strength. The presence of a quasi-continuum is the cause of the partially non-exponential nature of the atomic disintegration

Note: a novel vacuum ultraviolet light source assembly with aluminum-coated electrodes for enhancing the ionization efficiency of photoionization mass spectrometry.

Science.gov (United States)

Zhu, Zhixiang; Wang, Jian; Qiu, Keqing; Liu, Chengyuan; Qi, Fei; Pan, Yang

2014-04-01

A novel vacuum ultraviolet (VUV) light source assembly (VUVLSA) for enhancing the ionization efficiency of photoionization mass spectrometer has been described. The VUVLSA composes of a Krypton lamp and a pair of disk electrodes with circular center cavities. The two interior surfaces that face the photoionization region were aluminum-coated. VUV light can be reflected back and forth in the photoionization region between the electrodes, thus the photoionization efficiency can be greatly enhanced. The performances of two different shaped electrodes, the coated double flat electrodes (DFE), and double conical electrodes, were studied. We showed that the signal amplification of coated DFE is around 4 times higher than that of uncoated electrodes without VUV light reflection. The relationship between the pressure of ionization chamber and mass signal enhancement has also been studied.

Rotationally resolved flurorescence as a probe of molecular photoionization dynamics

International Nuclear Information System (INIS)

Poliakoff, E.D.; Kakar, S.; Choi, H.C.

1993-01-01

We present rotationally resolved data for N 2 (2σ u -1 ) photoionization in the excitation energy range 19 ≤ hν ≤ 35 eV. These are the first rotationally resolved measurements on the photoion over an extended spectral range above the ionization threshold. The requisite resolution is obtained by measuring rotationally resolved fluorescence from electronically excited photoions created by synchrotron radiation. This technique is useful for studying dynamical features embedded deep in the ionization continua and should supplement laser-based methods that are limited to probing near-threshold phenomena. The present study shows that the outgoing photoelectron can alter the rotational motion of the more massive photoion by exchanging angular momentum and this partitioning of angular momentum depends on the ionization dynamics. Thus, our data directly probe electron-molecule interactions and are sensitive probes of scattering dynamics. We are currently investigating dynamical features such as shape resonances and Cooper minima with rotational resolution for deciphering microscopic aspects of molecular scattering and these efforts will be discussed

Laser-enhanced ionization spectroscopy around the ionization limit

International Nuclear Information System (INIS)

Axner, O.; Berglind, T.; Sjoestroem, S.

1986-01-01

Laser-induced photoionization and Laser-Enhanced collision Ionization (LEI) of Na, Tl, and Li in flames are detected by measuring the production of charges following a laser excitation. The ionization signal is investigated for excitations of the atoms from lower lying states both to Rydberg states close to the ionization limit, as well as to continuum states, i.e. the process of collision ionization is compared with that of photoionization. The qualitative behaviour of the ionization signal when scanning across the ionization limit is studied. It is shown that the ionization signal has a smooth behaviour when passing from bound states into continuum states. The laser-induced photoionization signal strength of atoms in flames is both calculated and measured and a good agreement is obtained. A calculation of wavelength dependent photoionization signal strengths for a number of elements is also presented. Photoionization is used to determine flame- and geometry-dependent parameters. An implication of photoionization in connection with LEI spectrometry for trace element analysis is that there will be a significant increase in background noise if the sample contains high concentrations of easily photoionizing elements and short wavelength light is used. (orig.)

Investigating the Fundamentals of Molecular Depth Profiling Using Strong-field Photoionization of Sputtered Neutrals

Science.gov (United States)

Willingham, D.; Brenes, D. A.; Winograd, N.; Wucher, A.

2010-01-01

Molecular depth profiles of model organic thin films were performed using a 40 keV C60+ cluster ion source in concert with TOF-SIMS. Strong-field photoionization of intact neutral molecules sputtered by 40 keV C60+ primary ions was used to analyze changes in the chemical environment of the guanine thin films as a function of ion fluence. Direct comparison of the secondary ion and neutral components of the molecular depth profiles yields valuable information about chemical damage accumulation as well as changes in the molecular ionization probability. An analytical protocol based on the erosion dynamics model is developed and evaluated using guanine and trehalose molecular secondary ion signals with and without comparable laser photoionization data. PMID:26269660

Photoionization and cold collision studies using trapped atoms

International Nuclear Information System (INIS)

Gould, P.L.

1996-01-01

The authors have used laser cooling and trapping techniques to investigate photoionization and cold collisions. With laser-trapped Rb, they have measured the photoionization cross section from the first excited (5P) level by observing the photoionization-induced loss rate of neutral atoms from the trap. This technique has the advantage that it directly measures the photoionization rate per atom. Knowing the ionizing laser intensity and the excited-state fraction, the measured loss rate gives the absolute cross section. Using this technique, the Rb 5P photoionization cross section at ∼400 nm has been determined with an uncertainty of 9%. The authors are currently attempting to extend this method to the 5D level. Using time-ordered pulses of diode-laser light (similar to the STIRAP technique), they have performed very efficient two-photon excitation of trapped Rb atoms to 5D. Finally, they will present results from a recent collaboration which combines measurements form conventional molecular spectroscopy (single photon and double resonance) with photoassociation collisions of ultracold Na atoms to yield a precise (≤1 ppm) value for the dissociation energy of the X Σ g+ ground state of the Na 2 molecule

Streamer head structure: role of ionization and photoionization

International Nuclear Information System (INIS)

Nudnova, M M; Starikovskii, A Yu

2008-01-01

Results from experiments and numerical modelling of streamer propagation are presented. The 2D hydrodynamic numerical description of the pulsed discharge based on the local ionization and photoionization models adequately describes the streamer shape and dynamics over a wide range of pressures and voltages. This work presents a method for imaging the instantaneous emission distribution in the streamer head. A method for restoring the electrodynamic radius of the streamer head was developed on the basis of the streamer head images that were obtained with subnanosecond exposure time. The electrodynamic radius has been determined as the distance between the maxima of the electric field at the position where the streamer head transforms into the streamer channel. The dependence of the electrodynamic radius on voltage and pressure has been determined. We show that a 2D numerical model using hydrodynamic approximation predicts the streamer characteristics with an accuracy of about 15% in the 0.5-1 atmosphere pressure range and up to 40% in the 0.2-0.3 atmosphere pressure range for a voltage of U from 20 kV up to 40 kV in the 30 and 40 mm discharge gap.

The updated bottom up solution applied to atmospheric pressure photoionization and electrospray ionization mass spectrometry

Science.gov (United States)

The Updated Bottom Up Solution (UBUS) was recently applied to atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) of triacylglycerols (TAGs). This report demonstrates that the UBUS applies equally well to atmospheric pressure photoionization (APPI) MS and to electrospray ionizatio...

Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization.

Science.gov (United States)

Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

2016-08-01

The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M(+.) decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques. Graphical Abstract ᅟ.

LARGE-SCALE SHOCK-IONIZED AND PHOTOIONIZED GAS IN M83: THE IMPACT OF STAR FORMATION

International Nuclear Information System (INIS)

Hong, Sungryong; Calzetti, Daniela; Dopita, Michael A.; Blair, William P.; Whitmore, Bradley C.; Bond, Howard E.; Balick, Bruce; Carollo, Marcella; Disney, Michael J.; Frogel, Jay A.; Hall, Donald; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Paresce, Francesco; Saha, Abhijit; Silk, Joseph I.; Trauger, John T.; Walker, Alistair R.

2011-01-01

We investigate the ionization structure of the nebular gas in M83 using the line diagnostic diagram, [O III](5007 A)/Hβ versus [S II](6716 A+6731 A)/Hα, with the newly available narrowband images from the Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the diagnostic diagram on a pixel-by-pixel (0.''2 x 0.''2) basis and compare it with several photo- and shock-ionization models. We select four regions from the center to the outer spiral arm and compare them in the diagnostic diagram. For the photoionized gas, we observe a gradual increase of the log ([O III]/Hβ) ratios from the center to the spiral arm, consistent with the metallicity gradient, as the H II regions go from super-solar abundance to roughly solar abundance from the center out. Using the diagnostic diagram, we separate the photoionized from the shock-ionized component of the gas. We find that the shock-ionized Hα emission ranges from ∼2% to about 15%-33% of the total, depending on the separation criteria used. An interesting feature in the diagnostic diagram is a horizontal distribution around log ([O III]/Hβ) ∼ 0. This feature is well fit by a shock-ionization model with 2.0 Z sun metallicity and shock velocities in the range of 250-350 km s -1 . A low-velocity shock component, -1 , is also detected and is spatially located at the boundary between the outer ring and the spiral arm. The low-velocity shock component can be due to (1) supernova remnants located nearby, (2) dynamical interaction between the outer ring and the spiral arm, and (3) abnormal line ratios from extreme local dust extinction. The current data do not enable us to distinguish among those three possible interpretations. Our main conclusion is that, even at the HST resolution, the shocked gas represents a small fraction of the total ionized gas emission at less than 33% of the total. However, it accounts for virtually all of the mechanical energy produced by the central starburst in M83.

Combined corona discharge and UV photoionization source for ion mobility spectrometry.

Science.gov (United States)

Bahrami, Hamed; Tabrizchi, Mahmoud

2012-08-15

An ion mobility spectrometer is described which is equipped with two non-radioactive ion sources, namely an atmospheric pressure photoionization and a corona discharge ionization source. The two sources cannot only run individually but are additionally capable of operating simultaneously. For photoionization, a UV lamp was mounted parallel to the axis of the ion mobility cell. The corona discharge electrode was mounted perpendicular to the UV radiation. The total ion current from the photoionization source was verified as a function of lamp current, sample flow rate, and drift field. Simultaneous operation of the two ionization sources was investigated by recording ion mobility spectra of selected samples. The design allows one to observe peaks from either the corona discharge or photoionization individually or simultaneously. This makes it possible to accurately compare peaks in the ion mobility spectra from each individual source. Finally, the instrument's capability for discriminating two peaks appearing in approximately identical drift times using each individual ionization source is demonstrated. Copyright © 2012 Elsevier B.V. All rights reserved.

Inner-shell photoionization in weak and strong radiation fields

International Nuclear Information System (INIS)

Southworth, S.H.; Dunford, R.W.; Ederer, D.L.; Kanter, E.P.; Kraessig, B.; Young, L.

2004-01-01

The X-ray beams presently produced at synchrotron-radiation facilities interact weakly with matter, and the observation of double photoionization is due to electron-electron interactions. The intensities of future X-ray free-electron lasers are expected to produce double photoionization by absorption of two photons. The example of double K-shell photoionization of neon is discussed in the one- and two-photon cases. We also describe an experiment in which X rays photoionize the K shell of krypton in the presence of a strong AC field imposed by an optical laser

The ionization mechanisms in direct and dopant-assisted atmospheric pressure photoionization and atmospheric pressure laser ionization.

Science.gov (United States)

Kauppila, Tiina J; Kersten, Hendrik; Benter, Thorsten

2014-11-01

A novel, gas-tight API interface for gas chromatography-mass spectrometry was used to study the ionization mechanism in direct and dopant-assisted atmospheric pressure photoionization (APPI) and atmospheric pressure laser ionization (APLI). Eight analytes (ethylbenzene, bromobenzene, naphthalene, anthracene, benzaldehyde, pyridine, quinolone, and acridine) with varying ionization energies (IEs) and proton affinities (PAs), and four common APPI dopants (toluene, acetone, anisole, and chlorobenzene) were chosen. All the studied compounds were ionized by direct APPI, forming mainly molecular ions. Addition of dopants suppressed the signal of the analytes with IEs above the IE of the dopant. For compounds with suitable IEs or Pas, the dopants increased the ionization efficiency as the analytes could be ionized through dopant-mediated gas-phase reactions, such as charge exchange, proton transfer, and other rather unexpected reactions, such as formation of [M + 77](+) in the presence of chlorobenzene. Experiments with deuterated toluene as the dopant verified that in case of proton transfer, the proton originated from the dopant instead of proton-bound solvent clusters, as in conventional open or non-tight APPI sources. In direct APLI using a 266 nm laser, a narrower range of compounds was ionized than in direct APPI, because of exceedingly high IEs or unfavorable two-photon absorption cross-sections. Introduction of dopants in the APLI system changed the ionization mechanism to similar dopant-mediated gas-phase reactions with the dopant as in APPI, which produced mainly ions of the same form as in APPI, and ionized a wider range of analytes than direct APLI.

A VUV photoionization measurement and ab-initio calculation of the ionization energy of gas phase SiO2

Energy Technology Data Exchange (ETDEWEB)

Kostko, Oleg; Ahmed, Musahid; Metz, Ricardo B.

2008-12-05

In this work we report on the detection and vacuum-ultraviolet (VUV) photoionization of gas phase SiO2 generated in situ via laser ablation of silicon in a CO2 molecular beam. The resulting species are investigated by single photon ionization with tunable VUV synchrotron radiation and mass analyzed using reflectron mass spectrometry. Photoionization efficiency (PIE) curves are recorded for SiO and SiO2 and ionization energy estimates are revealed from such measurements. A state-to-state ionizationenergy of 12.60 (+-0.05) eV is recorded by fitting two prominent peaks in the PIE curve for the following process: 1SUM O-Si-O --> 2PRODg [O-Si-O]+. Electronic structure calculations aid in the interpretation of the photoionization process and allow for identification of the symmetric stretch of 2PRODg [O-Si-O]+ which is observed in the PIE spectrum to be 0.11 eV (890 cm-1) above the ground state of the cation and agrees with the 892 cm-1 symmetric stretch frequency calculated at the CCSD(T)/aug-cc-pVTZ level.

Dynamics of photoionization from molecular electronic wavepacket states in intense pulse laser fields: A nonadiabatic electron wavepacket study.

Science.gov (United States)

Matsuoka, Takahide; Takatsuka, Kazuo

2017-04-07

A theory for dynamics of molecular photoionization from nonadiabatic electron wavepackets driven by intense pulse lasers is proposed. Time evolution of photoelectron distribution is evaluated in terms of out-going electron flux (current of the probability density of electrons) that has kinetic energy high enough to recede from the molecular system. The relevant electron flux is in turn evaluated with the complex-valued electronic wavefunctions that are time evolved in nonadiabatic electron wavepacket dynamics in laser fields. To uniquely rebuild such wavefunctions with its electronic population being lost by ionization, we adopt the complex-valued natural orbitals emerging from the electron density as building blocks of the total wavefunction. The method has been implemented into a quantum chemistry code, which is based on configuration state mixing for polyatomic molecules. Some of the practical aspects needed for its application will be presented. As a first illustrative example, we show the results of hydrogen molecule and its isotope substitutes (HD and DD), which are photoionized by a two-cycle pulse laser. Photon emission spectrum associated with above threshold ionization is also shown. Another example is taken from photoionization dynamics from an excited state of a water molecule. Qualitatively significant effects of nonadiabatic interaction on the photoelectron spectrum are demonstrated.

Fine- and hyperfine-structure effects in molecular photoionization. II. Resonance-enhanced multiphoton ionization and hyperfine-selective generation of molecular cations

Energy Technology Data Exchange (ETDEWEB)

Germann, Matthias; Willitsch, Stefan, E-mail: stefan.willitsch@unibas.ch [Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel (Switzerland)

2016-07-28

Resonance-enhanced multiphoton ionization (REMPI) is a widely used technique for studying molecular photoionization and producing molecular cations for spectroscopy and dynamics studies. Here, we present a model for describing hyperfine-structure effects in the REMPI process and for predicting hyperfine populations in molecular ions produced by this method. This model is a generalization of our model for fine- and hyperfine-structure effects in one-photon ionization of molecules presented in Paper I [M. Germann and S. Willitsch, J. Chem. Phys. 145, 044314 (2016)]. This generalization is achieved by covering two main aspects: (1) treatment of the neutral bound-bound transition including the hyperfine structure that makes up the first step of the REMPI process and (2) modification of our ionization model to account for anisotropic populations resulting from this first excitation step. Our findings may be used for analyzing results from experiments with molecular ions produced by REMPI and may serve as a theoretical background for hyperfine-selective ionization experiments.

Investigation of optimal photoionization schemes for Sm by multi-step resonance ionization

International Nuclear Information System (INIS)

Cha, H.; Song, K.; Lee, J.

1997-01-01

Excited states of Sm atoms are investigated by using multi-color resonance enhanced multiphoton ionization spectroscopy. Among the ionization signals one observed at 577.86 nm is regarded as the most efficient excited state if an 1-color 3-photon scheme is applied. Meanwhile an observed level located at 587.42 nm is regarded as the most efficient state if one uses a 2-color scheme. For 2-color scheme a level located at 573.50 nm from this first excited state is one of the best second excited state for the optimal photoionization scheme. Based on this ionization scheme various concentrations of standard solutions for samarium are determined. The minimum amount of sample which can be detected by a 2-color scheme is determined as 200 fg. The detection sensitivity is limited mainly due to the pollution of the graphite atomizer. copyright 1997 American Institute of Physics

Attosecond delay in the molecular photoionization of asymmetric molecules.

Science.gov (United States)

Chacón, Alexis; Ruiz, Camilo

2018-02-19

We report theoretical calculations of the delay in photoemission from CO with particular emphasis on the role of the ultrafast electronic bound dynamics. We study the delays in photoionization in the HOMO and HOMO-1 orbitals of the CO molecule by looking into the stereo Wigner time delay technique. That compares the delay in photoemission from electrons emitted to the left and right to extract structural and dynamical information of the ionization process. For this we apply two techniques: The attosecond streak camera and the time of flight technique. Although they should provide the same results we have found large discrepancies of up to 36 in the case of HOMO, while for the HOMO-1 we obtain the same results with the two techniques. We have found that the large time delays observed in the HOMO orbital with the streaking technique are a consequence of the resonant transition triggered by the streaking field. This resonant transition produces a bound electron wavepacket that modifies the measurements of delay in photoionization. As a result of this observation, our technique allows us to reconstruct the bound wavepacket dynamics induced by the streaking field. By measuring the expected value of the electron momentum along the polarization direction after the streaking field has finished, we can recover the relative phase between the complex amplitudes of the HOMO and LUMO orbitals. These theoretical calculations pave the way for the measurement of ultrafast bound-bound electron transitionsand its crucial role for the delay in photoemission observation.

Molecular Frame Reconstruction Using Time-Domain Photoionization Interferometry.

Science.gov (United States)

Marceau, Claude; Makhija, Varun; Platzer, Dominique; Naumov, A Yu; Corkum, P B; Stolow, Albert; Villeneuve, D M; Hockett, Paul

2017-08-25

Photoionization of molecular species is, essentially, a multipath interferometer with both experimentally controllable and intrinsic molecular characteristics. In this work, XUV photoionization of impulsively aligned molecular targets (N_{2}) is used to provide a time-domain route to "complete" photoionization experiments, in which the rotational wave packet controls the geometric part of the photoionization interferometer. The data obtained is sufficient to determine the magnitudes and phases of the ionization matrix elements for all observed channels, and to reconstruct molecular frame interferograms from lab frame measurements. In principle, this methodology provides a time-domain route to complete photoionization experiments and the molecular frame, which is generally applicable to any molecule (no prerequisites), for all energies and ionization channels.

Multiphoton ionization of atomic cesium

International Nuclear Information System (INIS)

Compton, R.N.; Klots, C.E.; Stockdale, J.A.D.; Cooper, C.D.

1984-01-01

We describe experimental studies of resonantly enhanced multi-photon ionization (MPI) of cesium atoms in the presence and absence of an external electric field. In the zero-field studies, photo-electron angular distributions for one- and two-photon resonantly enhanced MPI are compared with the theory of Tang and Lambropoulos. Deviations of experiment from theory are attributed to hyperfine coupling effects in the resonant intermediate state. The agreement between theory and experiment is excellent. In the absence of an external electric field, signal due to two-photon resonant three-photon ionization of cesium via np states is undetectable. Application of an electric field mixes nearby nd and ns levels, thereby inducing excitation and subsequent ionization. Signal due to two-photon excitation of ns levels in field-free experiments is weak due to their small photoionization cross section. An electric field mixes nearby np levels which again allows detectable photo-ionization signal. For both ns and np states the ''field induced'' MPI signal increases as the square of the electric field for a given principal quantum number and increases rapidly with n for a given field strength

Photoionization cross section of atomic and molecular oxygen

International Nuclear Information System (INIS)

Pareek, P.N.

1983-01-01

Photoionization cross sections of atomic oxygen and dissociative photoionization cross sections of molecular oxygen were measured from their respective thresholds to 120 angstrom by use of a photoionization mass spectrometer in conjunction with a spark light source. The photoionization cross sections O 2 + parent ion and O + fragment ion from neutral O 2 were obtained by a technique that eliminated the serious problem of identifying the true abundances of O + ions. These ions are generally formed with considerable kinetic energy and, because most mass spectrometers discriminate against energetic ions, true O + abundances are difficult to obtain. In the present work the relative cross sections for producing O + ions are obtained and normalized against the total cross sections in a spectral region where dissociative ionization is not possible. The fragmentation cross sections for O + were then obtained by subtraction of O 2 + cross sections from the known total photoionization cross sections. The results are compared with the previously published measurements. The absolute photoionization cross section of atomic oxygen sigma 8 /sub +/ was measured at 304 A. The actual number density of oxygen atoms within the ionization region was obtained by measuring the fraction of 0 2 molecules dissociated. This sigma/sub +/ at 304 angstrom was used to convert the relative photoinization cross sections, measured as a function of wavelength using a calibrated photodiode, to absolute cross sections. The results are compared with previous measurements and calculated cross sections. angstrom Rydberg series converging to the OII 4 P state was observed

On the absolute photoionization cross section and dissociative photoionization of cyclopropenylidene.

Science.gov (United States)

Holzmeier, Fabian; Fischer, Ingo; Kiendl, Benjamin; Krueger, Anke; Bodi, Andras; Hemberger, Patrick

2016-04-07

We report the determination of the absolute photoionization cross section of cyclopropenylidene, c-C3H2, and the heat of formation of the C3H radical and ion derived by the dissociative ionization of the carbene. Vacuum ultraviolet (VUV) synchrotron radiation as provided by the Swiss Light Source and imaging photoelectron photoion coincidence (iPEPICO) were employed. Cyclopropenylidene was generated by pyrolysis of a quadricyclane precursor in a 1 : 1 ratio with benzene, which enabled us to derive the carbene's near threshold absolute photoionization cross section from the photoionization yield of the two pyrolysis products and the known cross section of benzene. The cross section at 9.5 eV, for example, was determined to be 4.5 ± 1.4 Mb. Upon dissociative ionization the carbene decomposes by hydrogen atom loss to the linear isomer of C3H(+). The appearance energy for this process was determined to be AE(0K)(c-C3H2; l-C3H(+)) = 13.67 ± 0.10 eV. The heat of formation of neutral and cationic C3H was derived from this value via a thermochemical cycle as Δ(f)H(0K)(C3H) = 725 ± 25 kJ mol(-1) and Δ(f)H(0K)(C3H(+)) = 1604 ± 19 kJ mol(-1), using a previously reported ionization energy of C3H.

Photoionization of three isomers of the C9H7 radical.

Science.gov (United States)

Hemberger, Patrick; Steinbauer, Michael; Schneider, Michael; Fischer, Ingo; Johnson, Melanie; Bodi, Andras; Gerber, Thomas

2010-04-15

Three resonance-stabilized radicals, 1-indenyl (Ind), 1-phenylpropargyl (1PPR), and 3-phenylpropargyl (3PPR), all isomers of the composition C(9)H(7), were generated by jet flash pyrolysis. Their photoionization was examined by VUV synchrotron radiation. The mass spectra show a clean and efficient radical generation when the pyrolysis is turned on. To study the photoionization, photoion yield measurements and threshold photoionization spectroscopy techniques were applied. We determined adiabatic ionization energies (IE(ad)) of 7.53 eV for Ind, 7.20 eV for 3PPR, and 7.4 eV for 1PPR. Ab initio calculations show no major change in geometry upon ionization, in agreement with ionization from a nonbonding molecular orbital. The IEs were also computed and are in agreement with the measured ones. The difference in the IE might allow a distinction of the three isomers in flames. In the indenyl spectrum, an excited a(+) (3)B(2) state of the cation was identified at 8.10 eV, which shows a low-energy vibrational progression of 61 meV. Furthermore, we have examined the dissociative photoionization of the precursors. The indenyl precursor, 1-indenyl bromide, undergoes dissociative photoionization to Ind(+). An appearance energy (AE(0K)) of 10.2 eV was obtained from fitting the experimental breakdown diagram. A binding energy of 1.8 eV can thus be determined for the C-Br bond in 1-indenyl bromide. The phenylpropargyl precursors 1PPBr (1-phenylpropargyl bromide/3-phenyl-3-bromopropyne) and 3PPBr (3-phenylpropargyl bromide/1-phenyl-3-bromopropyne) also lose a bromine atom upon dissociative photoionization. Approximate appearance energies of 9.8 eV for 3PPBr and 9.3 eV for 1PPBr have been determined.

Highly Resolved Studies of Vacuum Ultraviolet Photoionization Dynamics

Science.gov (United States)

Kakar, Sandeep

molecular aspects, such as the vibration and rotation, of photoionization dynamics over an extended spectral range when used in conjunction with synchrotron radiation as the exciting source. Furthermore, the high resolution made possible by this technique provides high selectivity for accessing weaker ionization channels which are the ones strongly affected by resonant activity, and the present study repeatedly stresses the importance of this capability in discovering and deciphering new trends in resonant molecular ionization dynamics.

Two-color photoionization and photoelectron studies by combining infrared and vacuum ultraviolet

International Nuclear Information System (INIS)

Ng, C.Y.

2005-01-01

Recent developments of two-color infrared (IR)-vacuum ultraviolet (VUV) and VUV-IR photoionization and photoelectron detection schemes for spectroscopic studies are described. By preparing molecules in selected rovibrational states by IR excitation prior to VUV-photoionization, state-selected and state-to-state photoionization cross sections can be obtained by IR-VUV-photoionization efficiency (IR-VUV-PIE) and IR-VUV-pulsed field ionization-photoelectron (IR-VUV-PFI-PE) measurements, respectively. Rotationally resolved autoionizing Rydberg states converging to excited ionic states, which cannot be observed by single-photon VUV-PIE measurements, can be examined by the IR-VUV-PIE scheme. By monitoring the photoion and the PFI-PE intensities at a fixed VUV energy as a function of IR frequency, the respective IR photoion and IR absorption spectra of the corresponding neutral molecule can be measured. Two-color VUV-IR photo-induced Rydberg ionization (PIRI) experiment, in which high-n Rydberg states are prepared by VUV-photoexcitation followed by IR-induced autoionization, has also been demonstrated. Since the IR-VUV-PIE, IR-VUV-PFI-PE, and VUV-IR-PIRI methods do not require the existence of a bound intermediate electronic state in the UV and are generally applicable to all molecules, the development of these two-color photoionization and photoelectron schemes is expected to significantly enhance the scope of VUV spectroscopy and chemistry

Inner-shell photo-ionized X-ray laser schemes for low-Z elements

International Nuclear Information System (INIS)

Moon, S.J.; Strobel, G.L.

1994-01-01

Gain calculations for inner-shell photo-ionized lasing in C at 45 angstrom are performed. An incident x-ray source represented by a 150 eV blackbody with a rise time of 50 fsec gives a gain of order 10 cm -1 . The x-ray source and thus the driving optical laser requirements are significantly reduced as compared to what is needed for Ne at 15 angstrom. The authors expect that existing ultra-short pulse lasers can produce the required x-ray source and thus produce a table-top x-ray laser at 45 angstrom

PHOTOIONIZATION IN THE SOLAR WIND

Energy Technology Data Exchange (ETDEWEB)

Landi, E.; Lepri, S. T., E-mail: elandi@umich.edu [Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109 (United States)

2015-10-20

In this work we investigate the effects of photoionization on the charge state composition of the solar wind. Using measured solar EUV and X-ray irradiance, the Michigan Ionization Code and a model for the fast and slow solar wind, we calculate the evolution of the charge state distribution of He, C, N, O, Ne, Mg, Si, S, and Fe with and without including photoionization for both types of wind. We find that the solar radiation has significant effects on the charge state distribution of C, N, and O, causing the ionization levels of these elements to be higher than without photoionization; differences are largest for oxygen. The ions commonly observed for elements heavier than O are much less affected, except in ICMEs where Fe ions more ionized than 16+ can also be affected by the solar radiation. We also show that the commonly used O{sup 7+}/O{sup 6+} density ratio is the most sensitive to photoionization; this sensitivity also causes the value of this ratio to depend on the phase of the solar cycle. We show that the O{sup 7+}/O{sup 6+} ratio needs to be used with caution for solar wind classification and coronal temperature estimates, and recommend the C{sup 6+}/C{sup 4+} ratio for these purposes.

Photoionization and molecular structure

International Nuclear Information System (INIS)

Palma, A.

1983-01-01

A presentation is here given of the theoretical work on photoionization and molecular structure carried out by the author and coworkers. The implications of the photoionization process on the molecular geometry are emphasized. In particular, the ionization effect on deep orbitals is considered and it is shown that, contrary to traditional thinking, these orbitals have relevant effects on the molecular geometry. The problem of calculating photoionization relative intensities for the full spectrum is also considered, and the results of the present model are compared with experimental and other theoretical results. (author)

PHOTOIONIZATION OF HIGH-ALTITUDE GAS IN A SUPERNOVA-DRIVEN TURBULENT INTERSTELLAR MEDIUM

International Nuclear Information System (INIS)

Wood, Kenneth; Hill, Alex S.; Haffner, L. Matthew; Reynolds, R. J.; Joung, M. Ryan; Mac Low, Mordecai-Mark; Benjamin, Robert A.; Madsen, G. J.

2010-01-01

We investigate models for the photoionization of the widespread diffuse ionized gas (DIG) in galaxies. In particular, we address the long standing question of the penetration of Lyman continuum photons from sources close to the galactic midplane to large heights in the galactic halo. We find that recent hydrodynamical simulations of a supernova-driven interstellar medium (ISM) have low-density paths and voids that allow for ionizing photons from midplane OB stars to reach and ionize gas many kiloparsecs above the midplane. We find that ionizing fluxes throughout our simulation grids are larger than predicted by one-dimensional slab models, thus allowing for photoionization by O stars of low altitude neutral clouds in the Galaxy that are also detected in Hα. In previous studies of such clouds, the photoionization scenario had been rejected and the Hα had been attributed to enhanced cosmic ray ionization or scattered light from midplane H II regions. We do find that the emission measure distributions in our simulations are wider than those derived from Hα observations in the Milky Way. In addition, the horizontally averaged height dependence of the gas density in the hydrodynamical models is lower than inferred in the Galaxy. These discrepancies are likely due to the absence of magnetic fields in the hydrodynamic simulations and we discuss how magnetohydrodynamic effects may reconcile models and observations. Nevertheless, we anticipate that the inclusion of magnetic fields in the dynamical simulations will not alter our primary finding that midplane OB stars are capable of producing high-altitude DIG in a realistic three-dimensional ISM.

Simulation of self-focusing of laser beam through medium with multi-step photo-ionization

International Nuclear Information System (INIS)

Akaoka, Katsuaki; Wakaida, Ikuo; Arisawa, Takashi

1995-01-01

We built a computation code for the coupled nonlinear Maxwell-Density Matrix equations of multi-level atomic systems including transverse and time-dependent variations. Numerical solutions for two-level atomic systems shown as a function of laser detuning in Na and U are in good agreement with the experimental result. Applying this code to the laser beam propagation through medium with two-step photo-ionization, it is concluded that the group velocity in the spatial edge of a laser pulse is slower than that in the center, and the self-focusing and the temporal reshaping of the laser pulse used for the first-excitation are more distinguished than that used for ionization. (author)

Revealing isomerism in sodium-water clusters: Photoionization spectra of Na(H2O)n (n = 2-90)

Science.gov (United States)

Dierking, Christoph W.; Zurheide, Florian; Zeuch, Thomas; Med, Jakub; Parez, Stanislav; Slavíček, Petr

2017-06-01

Soft ionization of sodium tagged polar clusters is increasingly used as a powerful technique for sizing and characterization of small aerosols with possible application, e.g., in atmospheric chemistry or combustion science. Understanding the structure and photoionization of the sodium doped clusters is critical for such applications. In this work, we report on measurements of photoionization spectra for sodium doped water clusters containing 2-90 water molecules. While most of the previous studies focused on the ionization threshold of the Na(H2O)n clusters, we provide for the first time full photoionization spectra, including the high-energy region, which are used as reference for a comparison with theory. As reported in previous work, we have seen an initial drop of the appearance ionization energy with cluster size to values of about 3.2 eV for n electron cloud. The appearance ionization energy is determined by isomers with fully solvated sodium and a highly delocalized electron cloud, while both fully and incompletely solvated isomers with localized electron clouds can contribute to the high energy part of the photoionization spectrum. Simulations at elevated temperatures show an increased abundance of isomers with low ionization energies, an entropic effect enabling size selective infrared action spectroscopy, based on near threshold photoionization of Na(H2O)n clusters. In addition, simulations of the sodium pick-up process were carried out to study the gradual formation of the hydrated electron which is the basis of the sodium-tagging sizing.

Multiphoton ionization of atomic cesium

International Nuclear Information System (INIS)

Compton, R.N.; Klots, C.E.; Stockdale, J.A.D.; Cooper, C.D.

1984-01-01

We describe experimental studies of resonantly enhanced multiphoton ionization (MPI) of cesium atoms in the presence and absence of an external electric field. In the zero-field studies, photoelectron angular distributions for one- and two-photon resonantly enhanced MPI are compared with the theory of Tang and Lambropoulos. Deviations of experiment from theory are attributed to hyperfine coupling effects in the resonant intermediate state. The agreement between theory and experiment is excellent. In the absence of an external electric field, signal due to two-photon resonant three-photon ionization of cesium via np states is undetectable. Application of an electric field mixes nearby nd and ns levels, thereby inducing excitation and subsequent ionization. Signal due to two-photon excitation of ns levels in field-free experiments is weak due to their small photoionization cross section. An electric field mixes nearby np levels which again allows detectable photoionization signal. For both ns and np states the field induced MPI signal increases as the square of the electric field for a given principal quantum number and increases rapidly with n for a given field strength. Finally, we note that the classical two-photon field-ionization threshold is lower for the case in which the laser polarization and the electric field are parallel than it is when they are perpendicular. 22 references, 11 figures

Photoionization cross-section of shallow donors impurities at all magnetic fields

International Nuclear Information System (INIS)

Zorkani, I.; Filali, L.

1998-09-01

The dependence of the photoionization cross-section for shallow donors on photon energy is calculated. The effects of strong and weak magnetic fields are considered by means of a variational wave function which is a linear combination of the cylindrical wave function and the oscillator one. Simple analytical expressions, valid for all magnetic fields, are obtained. It has been found that the photoionization cross-section is affected by the magnetic field. We give some results of Germanium. (author)

Photoionization studies with molecular beams

International Nuclear Information System (INIS)

Ng, C.Y.

1976-09-01

A molecular beam photoionization apparatus which combines the advantages of both the molecular beam method with photoionization mass spectrometry has been designed and constructed for carrying out some unique photoionization experiments. Rotational cooling during the supersonic expansion has resulted in high resolution photoionization efficiency curves for NO, ICl, C 2 H 2 and CH 3 I. The analysis of these spectra has yielded ionization potentials for these molecules to an accuracy of +- 3 MeV. Detailed autoionization structures were also resolved. This allows the investigation of the selection rules for autoionization, and the identification of the Rydberg series which converge to the excited states of the molecular ions. The degree of relaxation for thermally populated excited states has been examined using NO and ICl as examples. As a result of adiabatic cooling, a small percentage of dimers is also formed during the expansion. The photoionization efficiency curves for (NO) 2 , ArICl, Ar 2 , Kr 2 and Xe 2 have been obtained near the thresholds. Using the known dissociation energies of the (NO) 2 , Ar 2 , Kr 2 and Xe 2 van der Waals molecules, the corresponding dissociation energies for NO-NO + , Ar 2 + , Kr 2 + , and Xe 2 + have been determined. The ionization mechanisms for this class of molecules are examined and discussed

Determination of ionization energies of CnN (n=4-12): Vacuum-ultraviolet (VUV) photoionization experiments and theoretical calculations

International Nuclear Information System (INIS)

Kostko, Oleg; Zhou, Jia; Sun, Bian Jian; Lie, Jie Shiuan; Chang, Agnes H.H.; Kaiser, Ralf I.; Ahmed, Musahid

2010-01-01

Results from single photon vacuum ultraviolet photoionization of astrophysically relevant CnN clusters, n = 4 - 12, in the photon energy range of 8.0 eV to 12.8 eV are presented. The experimental photoionization efficiency curves, combined with electronic structure calculations, provide improved ionization energies of the CnN species. A search through numerous nitrogen-terminated CnN isomers for n=4-9 indicates that the linear isomer has the lowest energy, and therefore should be the most abundant isomer in the molecular beam. Comparison with calculated results also shed light on the energetics of the linear CnN clusters, particularly in the trends of the even-carbon and the odd-carbon series. These results can help guide the search of potential astronomical observations of these neutral molecules together with their cations in highly ionized regions or regions with a high UV/VUV photon flux (ranging from the visible to VUV with flux maxima in the Lyman-a region) in the interstellar medium.

Photoionization and dissociative photoionization study of HFC-152a using synchrotron radiation

International Nuclear Information System (INIS)

Huang Chaoqun; Wei Lixia; Yang Bin; Yang Rui; Wang Sisheng; Shan Xiaobin; Qi Fei; Zhang Yunwu; Sheng Liusi; Hao Liqing; Zhou Shikang; Wang Zhenya

2006-01-01

Photoionization and dissociative photoionization of HFC-152a have been studied using synchrotron radiation and a reflection time-of-flight mass spectrometry (RTOF-MS). The ionization energy of parent molecule (11.94 ± 0.04 eV) and appearance potentials of various fragment ions have been determined by measuring their photoionization efficiency curves. Energies, symmetry point groups and ground electronic states of neutrals and cations of parent and its fragments have been calculated using GAUSSIAN-03 program with the G3 method. According to the theoretical and experimental results, some dissociation channels and their dissociation energies of CH 3 CHF 2 + have been analyzed. (authors)

2008 Photoions, Photoionization & Photodetachment Gordon Research Conference January 27-February 1, 2008

Energy Technology Data Exchange (ETDEWEB)

Klaus Muller-Dethefs

2009-03-31

This conference brings together scientists interested in a range of basic phenomena linked to the ejection and scattering of electrons from atoms, molecules, clusters, liquids and solids by absorption of light. Photoionization, a highly sensitive probe of both structure and dynamics, can range from perturbative single-photon processes to strong-field highly non-perturbative interactions. It is responsible for the formation and destruction of molecules in astrophysical and plasma environments and successfully used in advanced analytical techniques. Positive ions, which can be produced and studied most effectively using photoionization, are the major components of all plasmas, vital constituents of flames and important intermediates in many chemical reactions. Negative ions are significant as transient species and, when photodetached, the corresponding neutral species often undergoes remarkable, otherwise non-observable, dynamics. The scope of the meeting spans from novel observations in atomic and molecular physics, such as Coulomb Crystals, highly excited states and cold Rydberg plasmas, to novel energy resolved or ultrafast time-resolved experiments, photoionization in strong laser fields, theoretical method development for electron scattering, photoionization and photodetachment and more complex phenomena such as charge transfer and DNA and protein conductivity, important for biological and analytical applications.

On possible structures of transverse ionizing shock waves

International Nuclear Information System (INIS)

Liberman, M.A.; Velikovich, A.L.

1978-01-01

The possible structures of ionizing shock waves propagating in gases across the magnetic field are investigated taking account of both ionization kinetics and the non-isothermality of the plasma which is formed within the shock front. It is shown that a definite factor in shaping the structure of the transverse ionizing shock wave is photo-ionization of the neutral gas across the front. The paper includes a study of the evolution of the transverse ionizing shock front with regard to photo-ionization, disclosing that a stable stationary shock structure emerges only in boundary conditions which are close to magnetohydrodynamic ones, i.e. upsilon 1 H 1 = upsilon 2 H 2 . In the case of strong transverse ionizing shock waves, when the flux of ionizing radiation across the front is great, the shock structure is obviously magnetohydrodynamic. (author)

Revealing isomerism in sodium-water clusters: Photoionization spectra of Na(H2O)n (n = 2-90).

Science.gov (United States)

Dierking, Christoph W; Zurheide, Florian; Zeuch, Thomas; Med, Jakub; Parez, Stanislav; Slavíček, Petr

2017-06-28

Soft ionization of sodium tagged polar clusters is increasingly used as a powerful technique for sizing and characterization of small aerosols with possible application, e.g., in atmospheric chemistry or combustion science. Understanding the structure and photoionization of the sodium doped clusters is critical for such applications. In this work, we report on measurements of photoionization spectra for sodium doped water clusters containing 2-90 water molecules. While most of the previous studies focused on the ionization threshold of the Na(H 2 O) n clusters, we provide for the first time full photoionization spectra, including the high-energy region, which are used as reference for a comparison with theory. As reported in previous work, we have seen an initial drop of the appearance ionization energy with cluster size to values of about 3.2 eV for nphotoionization spectrum. Simulations at elevated temperatures show an increased abundance of isomers with low ionization energies, an entropic effect enabling size selective infrared action spectroscopy, based on near threshold photoionization of Na(H 2 O) n clusters. In addition, simulations of the sodium pick-up process were carried out to study the gradual formation of the hydrated electron which is the basis of the sodium-tagging sizing.

Photoionization at relativistic energies

International Nuclear Information System (INIS)

Ionescu, D.C.; Technische Univ. Dresden; Soerensen, A.H.; Belkacem, A.

2000-11-01

At MeV energies and beyond the inner-shell vacancy production cross section associated with the photoelectric and Compton effect decrease with increasing photon energy. However, when the photon energy exceeds twice the rest energy of the electron, ionization of a bound electron may be catalyzed by the creation of an electron-positron pair. Distinctly different from all other known mechanisms for inner-shell vacancy production by photons, we show that the cross section for this ''vacuum-assisted photoionization'' increases with increasing photon energy and then saturates. As a main result, we predict that vacuum-assisted photoionization will dominate the other known photoionization mechanisms in the highly relativistic energy regime. (orig.)

DISSOCIATIVE PHOTOIONIZATION OF POLYCYCLIC AROMATIC HYDROCARBON MOLECULES CARRYING AN ETHYNYL GROUP

Energy Technology Data Exchange (ETDEWEB)

Rouillé, G.; Krasnokutski, S. A.; Fulvio, D.; Jäger, C. [Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena (Germany); Henning, Th. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Garcia, G. A.; Tang, X.-F.; Nahon, L., E-mail: cornelia.jaeger@uni-jena.de [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin BP 48, F-91192 Gif-sur-Yvette Cedex (France)

2015-09-10

The life cycle of the population of interstellar polycyclic aromatic hydrocarbon (PAH) molecules depends partly on the photostability of the individual species. We have studied the dissociative photoionization of two ethynyl-substituted PAH species, namely, 9-ethynylphenanthrene and 1-ethynylpyrene. Their adiabatic ionization energy and the appearance energy of fragment ions have been measured with the photoelectron photoion coincidence spectroscopy technique. The adiabatic ionization energy has been found at 7.84 ± 0.02 eV for 9-ethynylphenanthrene and at 7.41 ± 0.02 eV for 1-ethynylpyrene. These values are similar to those determined for the corresponding non-substituted PAH molecules phenanthrene and pyrene. The appearance energy of the fragment ion indicative of the loss of a H atom following photoionization is also similar for either ethynyl-substituted PAH molecule and its non-substituted counterpart. The measurements are used to estimate the critical energy for the loss of a H atom by the PAH cations and the stability of ethynyl-substituted PAH molecules upon photoionization. We conclude that these PAH derivatives are as photostable as the non-substituted species in H i regions. If present in the interstellar medium, they may play an important role in the growth of interstellar PAH molecules.

Photoionization cross-section of donor impurity in spherical quantum dots under electric and intense laser fields

International Nuclear Information System (INIS)

Burileanu, L.M.

2014-01-01

Using a perturbative method we have investigated the behavior of the binding energy and photoionization cross-section of a donor impurity in spherical GaAs–GaAlAs quantum dots under the influence of electric and intense high-frequency laser fields. The dependencies of the binding energy and photoionization cross-section on electric and laser field strength, dot radius and impurity position were investigated. Our results show that the amplitude of photoionization cross-section grows with the dot radius increase and the peak of the cross-section blue shifts with the laser intensity increment. We have found that the binding energy is not a monotonically function of laser intensity: it decreases or increases depending on electric field regime. The studied effects are even more pronounced as the quantum dot radius is smaller. -- Highlights: • A photoionization cross-section study in quantum dots under laser and electric fields. • The photoionization cross-section peaks are red shifted by the electric field. • The photoionization cross-section peaks are blue shifted by the laser field. • The combined effects of applied fields strongly affect the binding energy

Dissociative photoionization of the NO molecule studied by photoelectron-photon coincidence technique

International Nuclear Information System (INIS)

Kivimaeki, A.; Alvarez-Ruiz, J.; Coreno, M.; Simone, M. de; Moise, A.; Partanen, L.; Richter, R.; Stankiewicz, M.

2010-01-01

Low-energy photoelectron-vacuum ultraviolet (VUV) photon coincidences have been measured using synchrotron radiation excitation in the inner-valence region of the nitric oxide molecule. The capabilities of the coincidence set-up were demonstrated by detecting the 2s -1 → 2p -1 radiative transitions in coincidence with the 2s photoelectron emission in Ne. In NO, the observed coincidence events are attributed to dissociative photoionization with excitation, whereby photoelectron emission is followed by fragmentation of excited NO + ions into O + + N* or N + + O* and VUV emission from an excited neutral fragment. The highest coincidence rate occurs with the opening of ionization channels which are due to correlation satellites of the 3σ photoionization. The decay time of VUV photon emission was also measured, implying that specific excited states of N atoms contribute significantly to observed VUV emission.

Investigation of the ionization mechanism of polycyclic aromatic hydrocarbons using an ethanol/bromobenzene/chlorobenzene/anisole mixture as a dopant in liquid chromatography/atmospheric pressure photoionization mass spectrometry

KAUST Repository

Amad, Maan H.

2012-09-23

RATIONALE An ethanol-based multicomponent dopant consisting of ethanol/chlorobenzene/bromobenzene/anisole (98.975:0.1:0.9:0.025, v/v/v/v) has been used as a dopant for atmospheric pressure photoionization (APPI) of polycyclic aromatic hydrocarbons (PAHs). In this study the mechanism of ionization of PAHs assisted by the ethanol-based multicomponent dopant is investigated. METHODS The reactant background cluster ions of the ethanol-based multicomponent dopant observed in the positive ion APPI were studied. These studies were performed to investigate the mechanism behind the generation of a molecular radical cation (M +•) for PAHs by APPI assisted by the ethanol-based multicomponent dopant. Full scan and MS/MS analyses were conducted using an LTQ Orbitrap mass spectrometer. The effect of acidification of the mobile phase on the dopant cluster ion formation was also investigated. RESULTS With the ethanol-based multicomponent dopant, a single type of molecular radical cation M +• was observed for the studied PAHs. The characteristic ion signal of the multicomponent dopant mixture consisted of mainly anisole photoions at m/z 108.05697 and its adduct ions at m/z 124.05188 and 164.07061. The anisole ion response at m/z 108.05697 was stable in the presence of acetonitrile, methanol, water and 0.1% formic acid mobile phase composition. CONCLUSIONS The abundance formation of anisole photoions shows the universality of this multicomponent dopant in ionizing compounds with ionization energy ranging from 7.1-8.2 eV. Since the ionization energy of anisole is 8.2 eV and is lower than those of chlorobenzene (9.07 eV) and bromobenzene (9.0 eV), the mechanism of formation of anisole photoions even with its very minute amounts was not only governed by its photoionization by the krypton lamp photon energy (10.0 eV and 10.6 eV), but also by charge transfer from bromobenzene and chlorobenzene radical cations. PAH molecules were mainly ionized by charge transfer reaction from

Investigation of the ionization mechanism of polycyclic aromatic hydrocarbons using an ethanol/bromobenzene/chlorobenzene/anisole mixture as a dopant in liquid chromatography/atmospheric pressure photoionization mass spectrometry

KAUST Repository

Amad, Maan H.; Sioud, Salim

2012-01-01

RATIONALE An ethanol-based multicomponent dopant consisting of ethanol/chlorobenzene/bromobenzene/anisole (98.975:0.1:0.9:0.025, v/v/v/v) has been used as a dopant for atmospheric pressure photoionization (APPI) of polycyclic aromatic hydrocarbons (PAHs). In this study the mechanism of ionization of PAHs assisted by the ethanol-based multicomponent dopant is investigated. METHODS The reactant background cluster ions of the ethanol-based multicomponent dopant observed in the positive ion APPI were studied. These studies were performed to investigate the mechanism behind the generation of a molecular radical cation (M +•) for PAHs by APPI assisted by the ethanol-based multicomponent dopant. Full scan and MS/MS analyses were conducted using an LTQ Orbitrap mass spectrometer. The effect of acidification of the mobile phase on the dopant cluster ion formation was also investigated. RESULTS With the ethanol-based multicomponent dopant, a single type of molecular radical cation M +• was observed for the studied PAHs. The characteristic ion signal of the multicomponent dopant mixture consisted of mainly anisole photoions at m/z 108.05697 and its adduct ions at m/z 124.05188 and 164.07061. The anisole ion response at m/z 108.05697 was stable in the presence of acetonitrile, methanol, water and 0.1% formic acid mobile phase composition. CONCLUSIONS The abundance formation of anisole photoions shows the universality of this multicomponent dopant in ionizing compounds with ionization energy ranging from 7.1-8.2 eV. Since the ionization energy of anisole is 8.2 eV and is lower than those of chlorobenzene (9.07 eV) and bromobenzene (9.0 eV), the mechanism of formation of anisole photoions even with its very minute amounts was not only governed by its photoionization by the krypton lamp photon energy (10.0 eV and 10.6 eV), but also by charge transfer from bromobenzene and chlorobenzene radical cations. PAH molecules were mainly ionized by charge transfer reaction from

Photoionization spectroscopy of deep defects responsible for current collapse in nitride-based field effect transistors

International Nuclear Information System (INIS)

Klein, P B; Binari, S C

2003-01-01

This review is concerned with the characterization and identification of the deep centres that cause current collapse in nitride-based field effect transistors. Photoionization spectroscopy is an optical technique that has been developed to probe the characteristics of these defects. Measured spectral dependences provide information on trap depth, lattice coupling and on the location of the defects in the device structure. The spectrum of an individual trap may also be regarded as a 'fingerprint' of the defect, allowing the trap to be followed in response to the variation of external parameters. The basis for these measurements is derived through a modelling procedure that accounts quantitatively for the light-induced drain current increase in the collapsed device. Applying the model to fit the measured variation of drain current increase with light illumination provides an estimate of the concentrations and photoionization cross-sections of the deep defects. The results of photoionization studies of GaN metal-semiconductor field effect transistors and AlGaN/GaN high electron mobility transistors (HEMTs) grown by metal-organic chemical vapour deposition (MOCVD) are presented and the conclusions regarding the nature of the deep traps responsible are discussed. Finally, recent photoionization studies of current collapse induced by short-term (several hours) bias stress in AlGaN/GaN HEMTs are described and analysed for devices grown by both MOCVD and molecular beam epitaxy. (topical review)

Collective effects in isolated atoms (many-body aspects of photoionization process)

International Nuclear Information System (INIS)

Amusia, M.Y.

1983-01-01

This chapter examines outer and intermediate many-electron shells and demonstrates that photoionization is of collective nature because in the atomic reaction to the external electromagnetic field at least all electrons of the ionized subshell take part. Performs the calculation of complex atom photoionization using random phase approximation with exchange (RPAE). Explains that in RPAE the ionization amplitude is presented as a sum of two terms, describing the direct knock-out and the induced one which is connected with a variation of the self-consistent field, caused by polarization of atomic shells under the action of the external field. Discusses collective effects in outer shells; deviation from RPAE prediction in outer shells; excitations ''two electrons-two holes'' and autoionizing states; collective effects in inner shells; and bremsstrahlung. Observes a large number of many-particle effects which manifest themselves practically in all atomic processes. Finds that by correcting and improving the one-electron approximation it becomes possible even in its frame to include much of what seems to be many-electron corrections

Selectivity, specificity, and sensitivity in the photoionization of sputtered species

International Nuclear Information System (INIS)

Gruen, D.M.; Calaway, W.F.; Pellin, M.J.; Young, C.E.; Spiegel, D.R.; Clayton, R.N.; Davis, A.M.; Blum, J.D.

1990-01-01

To deal with the problem of non- or near-resonant ionization, one needs to achieve the highest selectively for photoionization of the species of interest relative to isobarically overlapping species by choosing a specific photoionization scheme tailoring are that is could not have near-overlap with known atomic or molecular energy levels of isobaric species, and that it should lead to saturation of the resonance transitions at the lowest possible laser power levels so as to minimize two- and three-photon nonresonant photoionization processes. Experience has shown that, even when these two conditions are met as closely as possible, non- or near-resonant ionization can still occur, perhaps because of the existence of hitherto unobserved energy levels, photodissociation of sputtered molecules, or other effects. It is becoming clear that maximizing detection sensitivity for a particular species requires one to pay careful attention to the selection of an optimal photoionization scheme. It is the purpose of the present paper to illustrate this point with several examples and to help point the way to still further improvements in detection sensitivity by non- or near-resonant. ionization through detailed exploration of alternative photoionization schemes

Photoionization studies with molecular beams

Energy Technology Data Exchange (ETDEWEB)

Ng, C.Y.

1976-09-01

A molecular beam photoionization apparatus which combines the advantages of both the molecular beam method with photoionization mass spectrometry has been designed and constructed for carrying out some unique photoionization experiments. Rotational cooling during the supersonic expansion has resulted in high resolution photoionization efficiency curves for NO, ICl, C/sub 2/H/sub 2/ and CH/sub 3/I. The analysis of these spectra has yielded ionization potentials for these molecules to an accuracy of +- 3 MeV. Detailed autoionization structures were also resolved. This allows the investigation of the selection rules for autoionization, and the identification of the Rydberg series which converge to the excited states of the molecular ions. The degree of relaxation for thermally populated excited states has been examined using NO and ICl as examples. As a result of adiabatic cooling, a small percentage of dimers is also formed during the expansion. The photoionization efficiency curves for (NO)/sub 2/, ArICl, Ar/sub 2/, Kr/sub 2/ and Xe/sub 2/ have been obtained near the thresholds. Using the known dissociation energies of the (NO)/sub 2/, Ar/sub 2/, Kr/sub 2/ and Xe/sub 2/ van der Waals molecules, the corresponding dissociation energies for NO-NO/sup +/, Ar/sub 2//sup +/, Kr/sub 2//sup +/, and Xe/sub 2//sup +/ have been determined. The ionization mechanisms for this class of molecules are examined and discussed.

Absolute photoionization cross section of the ethyl radical in the range 8-11.5 eV: synchrotron and vacuum ultraviolet laser measurements.

Science.gov (United States)

Gans, Bérenger; Garcia, Gustavo A; Boyé-Péronne, Séverine; Loison, Jean-Christophe; Douin, Stéphane; Gaie-Levrel, François; Gauyacq, Dolores

2011-06-02

The absolute photoionization cross section of C(2)H(5) has been measured at 10.54 eV using vacuum ultraviolet (VUV) laser photoionization. The C(2)H(5) radical was produced in situ using the rapid C(2)H(6) + F → C(2)H(5) + HF reaction. Its absolute photoionization cross section has been determined in two different ways: first using the C(2)H(5) + NO(2) → C(2)H(5)O + NO reaction in a fast flow reactor, and the known absolute photoionization cross section of NO. In a second experiment, it has been measured relative to the known absolute photoionization cross section of CH(3) as a reference by using the CH(4) + F → CH(3) + HF and C(2)H(6) + F → C(2)H(5) + HF reactions successively. Both methods gave similar results, the second one being more precise and yielding the value: σ(C(2)H(5))(ion) = (5.6 ± 1.4) Mb at 10.54 eV. This value is used to calibrate on an absolute scale the photoionization curve of C(2)H(5) produced in a pyrolytic source from the C(2)H(5)NO(2) precursor, and ionized by the VUV beam of the DESIRS beamline at SOLEIL synchrotron facility. In this latter experiment, a recently developed ion imaging technique is used to discriminate the direct photoionization process from dissociative ionization contributions to the C(2)H(5)(+) signal. The imaging technique applied on the photoelectron signal also allows a slow photoelectron spectrum with a 40 meV resolution to be extracted, indicating that photoionization around the adiabatic ionization threshold involves a complex vibrational overlap between the neutral and cationic ground states, as was previously observed in the literature. Comparison with earlier photoionization studies, in particular with the photoionization yield recorded by Ruscic et al. is also discussed. © 2011 American Chemical Society

Relativistic Photoionization Computations with the Time Dependent Dirac Equation

Science.gov (United States)

2016-10-12

Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6795--16-9698 Relativistic Photoionization Computations with the Time Dependent Dirac... Photoionization Computations with the Time Dependent Dirac Equation Daniel F. Gordon and Bahman Hafizi Naval Research Laboratory 4555 Overlook Avenue, SW...Unclassified Unlimited Unclassified Unlimited 22 Daniel Gordon (202) 767-5036 Tunneling Photoionization Ionization of inner shell electrons by laser

Solvent jet desorption capillary photoionization-mass spectrometry.

Science.gov (United States)

Haapala, Markus; Teppo, Jaakko; Ollikainen, Elisa; Kiiski, Iiro; Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

2015-03-17

A new ambient mass spectrometry method, solvent jet desorption capillary photoionization (DCPI), is described. The method uses a solvent jet generated by a coaxial nebulizer operated at ambient conditions with nitrogen as nebulizer gas. The solvent jet is directed onto a sample surface, from which analytes are extracted into the solvent and ejected from the surface in secondary droplets formed in collisions between the jet and the sample surface. The secondary droplets are directed into the heated capillary photoionization (CPI) device, where the droplets are vaporized and the gaseous analytes are ionized by 10 eV photons generated by a vacuum ultraviolet (VUV) krypton discharge lamp. As the CPI device is directly connected to the extended capillary inlet of the MS, high ion transfer efficiency to the vacuum of MS is achieved. The solvent jet DCPI provides several advantages: high sensitivity for nonpolar and polar compounds with limit of detection down to low fmol levels, capability of analyzing small and large molecules, and good spatial resolution (250 μm). Two ionization mechanisms are involved in DCPI: atmospheric pressure photoionization, capable of ionizing polar and nonpolar compounds, and solvent assisted inlet ionization capable of ionizing larger molecules like peptides. The feasibility of DCPI was successfully tested in the analysis of polar and nonpolar compounds in sage leaves and chili pepper.

Double-Exponentially Decayed Photoionization in CREI Effect: Numerical Experiment on 3D H2+

International Nuclear Information System (INIS)

Feng, Li; Ting-Ying, Wang; Gui-Zhong, Zhang; Wang-Hua, Xiang; III, W. T. Hill

2008-01-01

On the platform of the 3D H 2 + system, we perform a numerical simulation of its photoionization rate under excitation of weak to intense laser intensities with varying pulse durations and wavelengths. A novel method is proposed for calculating the photoionization rate: a double exponential decay of ionization probability is best suited for fitting this rate. Confirmation of the well-documented charge-resonance-enhanced ionization (CREI) effect at medium laser intensity and finding of ionization saturation at high light intensity corroborate the robustness of the suggested double-exponential decay process. Surveying the spatial and temporal variations of electron wavefunctions uncovers a mechanism for the double-exponentially decayed photoionization probability as onset of electron ionization along extra degree of freedom. Henceforth, the new method makes clear the origins of peak features in photoionization rate versus internuclear separation. It is believed that this multi-exponentially decayed ionization mechanism is applicable to systems with more degrees of motion

Combination of electrospray ionization, atmospheric pressure photoionization and laser desorption ionization Fourier transform ion cyclotronic resonance mass spectrometry for the investigation of complex mixtures – Application to the petroleomic analysis of bio-oils

Energy Technology Data Exchange (ETDEWEB)

Hertzog, Jasmine [LCP-A2MC, FR 2843 Institut Jean Barriol de Chimie et Physique Moléculaires et Biomoléculaires, FR 3624 Réseau National de Spectrométrie de Masse FT-ICR à très haut champ, Université de Lorraine, ICPM, 1 boulevard Arago, 57078 Metz Cedex 03 (France); Carré, Vincent, E-mail: vincent.carre@univ-lorraine.fr [LCP-A2MC, FR 2843 Institut Jean Barriol de Chimie et Physique Moléculaires et Biomoléculaires, FR 3624 Réseau National de Spectrométrie de Masse FT-ICR à très haut champ, Université de Lorraine, ICPM, 1 boulevard Arago, 57078 Metz Cedex 03 (France); Le Brech, Yann [LRGP, CNRS, Université de Lorraine, ENSIC, 1, Rue Grandville, 54000 Nancy (France); Mackay, Colin Logan [SIRCAMS, School of Chemistry, University of Edinburgh, Edinburgh, EH9 3FJ, Scotland (United Kingdom); Dufour, Anthony [LRGP, CNRS, Université de Lorraine, ENSIC, 1, Rue Grandville, 54000 Nancy (France); Mašek, Ondřej [UK Biochar Research Center, School of Geosciences, University of Edinburgh, Kings Buildings, Edinburgh, EH9 3JN (United Kingdom); and others

2017-05-29

The comprehensive description of complex mixtures such as bio-oils is required to understand and improve the different processes involved during biological, environmental or industrial operation. In this context, we have to consider how different ionization sources can improve a non-targeted approach. Thus, the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been coupled to electrospray ionization (ESI), laser desorption ionization (LDI) and atmospheric pressure photoionization (APPI) to characterize an oak pyrolysis bio-oil. Close to 90% of the all 4500 compound formulae has been attributed to C{sub x}H{sub y}O{sub z} with similar oxygen class compound distribution. Nevertheless, their relative abundance in respect with their double bound equivalent (DBE) value has evidenced significant differences depending on the ion source used. ESI has allowed compounds with low DBE but more oxygen atoms to be ionized. APPI has demonstrated the efficient ionization of less polar compounds (high DBE values and less oxygen atoms). The LDI behavior of bio-oils has been considered intermediate in terms of DBE and oxygen amounts but it has also been demonstrated that a significant part of the features are specifically detected by this ionization method. Thus, the complementarity of three different ionization sources has been successfully demonstrated for the exhaustive characterization by petroleomic approach of a complex mixture. - Highlights: • Non-targeted mass spectrometry by combining electrospray ionization, atmospheric pressure photoionization and laser/desorption ionization. • Exhaustive description of pyrolytic bio-oil components. • Distinction of sugaric derivatives, lignin derivatives and lipids contained in a woody-based pyrolytic bio-oil.

Surface-ionization field mass-spectrometry studies of nonequilibrium surface ionization

International Nuclear Information System (INIS)

Blashenkov, Nikolai M; Lavrent'ev, Gennadii Ya

2007-01-01

The ionization of polyatomic molecules on tungsten and tungsten oxide surfaces is considered for quasiequilibrium or essentially nonequilibrium conditions (in the latter case, the term nonequilibrium surface ionization is used for adsorbate ionization). Heterogeneous reactions are supposed to proceed through monomolecular decay of polyatomic molecules or fragments of multimolecular complexes. The nonequilibrium nature of these reactions is established. The dependences of the current density of disordered ions on the surface temperature, electric field strength, and ionized particle energy distribution are obtained in analytical form. Heterogeneous dissociation energies, the ionization potentials of radicals, and the magnitude of reaction departure from equilibrium are determined from experimental data, as are energy exchange times between reaction products and surfaces, the number of molecules in molecular complexes, and the number of effective degrees of freedom in molecules and complexes. In collecting the data a new technique relying on surface-ionization field mass-spectrometry was applied. (instruments and methods of investigation)

Photoionization from the 6p 2P3/2 state of neutral cesium

International Nuclear Information System (INIS)

Haq, S. U.; Nadeem, Ali

2010-01-01

We report the photoionization studies of cesium from the 6p 2 P 3/2 excited state to measure the photoionization cross section at and above the first ionization threshold, oscillator strength of the highly excited transitions, and extension in the Rydberg series. The photoionization cross section at the first ionization threshold is measured as 25 (4) Mb and at excess energies 0.02, 0.04, 0.07, and 0.09 eV as 21, 19, 17, and 16 Mb, respectively. Oscillator strength of the 6p 2 P 3/2 → nd 2 D 5/2 (23 ≤ n ≤ 60) Rydberg transitions has been extracted utilizing the threshold value of photoionization cross section and the recorded nd 2 D 5/2 photoionization spectra.

Photoionization Modeling

Science.gov (United States)

Kallman, T.

2010-01-01

Warm absorber spectra are characterized by the many lines from partially ionized intermediate-Z elements, and iron, detected with the grating instruments on Chandra and XMM-Newton. If these ions are formed in a gas which is in photoionization equilibrium, they correspond to a broad range of ionization parameters, although there is evidence for certain preferred values. A test for any dynamical model for these outflows is to reproduce these properties, at some level of detail. In this paper we present a statistical analysis of the ionization distribution which can be applied both the observed spectra and to theoretical models. As an example, we apply it to our dynamical models for warm absorber outflows, based on evaporation from the molecular torus.

Time-dependent Cooling in Photoionized Plasma

Energy Technology Data Exchange (ETDEWEB)

Gnat, Orly, E-mail: orlyg@phys.huji.ac.il [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel)

2017-02-01

I explore the thermal evolution and ionization states in gas cooling from an initially hot state in the presence of external photoionizing radiation. I compute the equilibrium and nonequilibrium cooling efficiencies, heating rates, and ion fractions for low-density gas cooling while exposed to the ionizing metagalactic background radiation at various redshifts ( z = 0 − 3), for a range of temperatures (10{sup 8}–10{sup 4} K), densities (10{sup −7}–10{sup 3} cm{sup −3}), and metallicities (10{sup −3}–2 times solar). The results indicate the existence of a threshold ionization parameter, above which the cooling efficiencies are very close to those in photoionization equilibrium (so that departures from equilibrium may be neglected), and below which the cooling efficiencies resemble those in collisional time-dependent gas cooling with no external radiation (and are thus independent of density).

Photodissociation of anisole and absolute photoionization cross-section of the phenoxy radical.

Science.gov (United States)

Xu, Hong; Pratt, S T

2013-11-21

We have studied the photodissociation dynamics of anisole (C6H5OCH3) at 193 nm and determined the absolute photoionization cross-section of the phenoxy radical at 118.2 nm (10.486 eV) relative to the known cross-section of the methyl radical. Even at this energy, there is extensive fragmentation of the phenoxy radical upon photoionization, which is attributed to ionizing transitions that populate low-lying excited electronic states of the cation. For phenoxy radicals with less than ∼1 eV of internal energy, we find a cross-section for the production of the phenoxy cation of 14.8 ± 3.8 Mb. For radicals with higher internal energy, dissociative ionization is the dominant process, and for internal energies of ∼2.7-3.7 eV, we find a total cross-section (photoionization plus dissociative ionization) of 22.3 ± 4.1 Mb. The results are discussed relative to the recently reported photoionization cross-section of phenol.

Combination of lasers and synchrotron radiation in studies of atomic photoionization

International Nuclear Information System (INIS)

Meyer, M.

2009-01-01

Recent experiments using the combination of conventional lasers and synchrotron radiation are presented and discussed. The controlled laser-manipulation of atoms prior to ionization by the synchrotron radiation provides an ideal experimental basis for detailed investigations of atomic photoionization. Due to the recent advances in high-resolution electron spectroscopy, it has become possible to analyze the J-resolved fine structure of the final ionic states in the photoionization of laser-excited atoms enabling thereby the determination of the specific influence of the outer electron to the ionization from inner subshells. Especially, the analysis of photoemission satellites and their relative intensities bring out directly the importance of electron correlations. Furthermore, it is shown through some examples of experiments using linearly and circularly polarized radiations, how the study of magnetic dichroisms in the photoionization opens the access to a complete description of the photoionization process, in particular to the determination of partial photoionization cross-sections.

Use of synchrotron and laser radiations for present and future photoionization studies in excited atoms and ions

International Nuclear Information System (INIS)

Wuilleumier, F.J.

1984-01-01

The status of experiments in photoionization of atoms in excited states is reviewed, with emphasis given to synchrotron and laser photon sources. A technique for exciting the photoionization spectrum of Na atoms using the flux emitted from the bending magnetic of a storage ring is discussed in detail. Some problems in interpreting photoionization spectrum of Ba in the excited state, due to the presence of higher orders are considered. A design approach for a positron storage ring to produce coherent radiation in the VUV is described. It is shown that combined use of a CW dye laser and the positron storage ring will allow new progress to be made in photoionization studies of excited atoms. Some of the experiments to be carried out using the positron storage ring include: measurements of collisional ionization in rare earth metal atoms of low atomic density; photoionization measurements at lower laser powers, leading to an extension of the CW tunability range; and photoionization studies of multiply charged positive ions. 21 references

Protonation enhancement by dichloromethane doping in low-pressure photoionization.

Science.gov (United States)

Shu, Jinian; Zou, Yao; Xu, Ce; Li, Zhen; Sun, Wanqi; Yang, Bo; Zhang, Haixu; Zhang, Peng; Ma, Pengkun

2016-12-01

Doping has been used to enhance the ionization efficiency of analytes in atmospheric pressure photoionization, which is based on charge exchange. Compounds with excellent ionization efficiencies are usually chosen as dopants. In this paper, we report a new phenomenon observed in low-pressure photoionization: Protonation enhancement by dichloromethane (CH 2 Cl 2 ) doping. CH 2 Cl 2 is not a common dopant due to its high ionization energy (11.33 eV). The low-pressure photoionization source was built using a krypton VUV lamp that emits photons with energies of 10.0 and 10.6 eV and was operated at ~500-1000 Pa. Protonation of water, methanol, ethanol, and acetaldehyde was respectively enhanced by 481.7 ± 122.4, 197.8 ± 18.8, 87.3 ± 7.8, and 93.5 ± 35.5 times after doping 291 ppmv CH 2 Cl 2 , meanwhile CH 2 Cl 2 almost does not generate noticeable ions itself. This phenomenon has not been documented in the literature. A new protonation process involving in ion-pair and H-bond formations was proposed to expound the phenomenon. The observed phenomenon opens a new prospect for the improvement of the detection efficiency of VUV photoionization.

Control of entanglement following the photoionization of trapped, hydrogen-like ions

International Nuclear Information System (INIS)

Radtke, Thomas; Fritzsche, Stephan; Surzhykov, Andrey

2005-01-01

Density matrix theory is applied to re-investigate the entanglement in the spin state of pairs of electrons following the photoionization of trapped, hydrogen-like ions. For the ionization of one out of two non-interacting atoms, in particular, we analyzed how the entanglement between the electrons is changed owing to their interaction with the radiation field. Detailed calculations on the concurrence of the final spin-state of the electrons have been performed for the photoionization of hydrogen as well as for hydrogen-like Xe 53+ and U 91+ ions. From these computations it is shown that the degree of entanglement, which is quite well preserved for neutral hydrogen, will be strongly affected by relativistic and non-dipole effects of the radiation field as the nuclear charge of the ions is increased

Atomic kinetics of a neon photoionized plasma experiment at Z

Science.gov (United States)

Mayes, Daniel C.; Mancini, Roberto; Bailey, James E.; Loisel, Guillaume; Rochau, Gregory; ZAPP Collaboration

2018-06-01

We discuss an experimental effort to study the atomic kinetics in astrophysically relevant photoionized plasmas via K-shell line absorption spectroscopy. The experiment employs the intense x-ray flux emitted at the collapse of a Z-pinch to heat and backlight a photoionized plasma contained within a cm-scale gas cell placed at a variable distance from the Z-pinch and filled with neon gas pressures in the range from 3.5 to 30 Torr. The experimental platform affords an order of magnitude range in the ionization parameter characterizing the photoionized plasma at the peak of the x-ray drive from about 5 to 80 erg*cm/s. Thus, the experiment allows for the study of trends in ionization distribution as a function of the ionization parameter. An x-ray crystal spectrometer capable of time-integrated and/or time-gated configurations is used to collect absorption spectra. The spectra show line absorption by several ionization stages of neon, including Be-, Li-, He-, and H-like ions. Analysis of these spectra yields ion areal densities and charge state distributions, which can be compared with simulation results from atomic kinetics codes. In addition, the electron temperature is extracted from level population ratios of nearby energy levels in Li- and Be-like ions, which can be used to test heating models of photoionized plasmas.

Interference effects on the photoionization cross sections between two neighbouring atoms: nitrogen as an example

International Nuclear Information System (INIS)

Jian-Hua, Wu; Jian-Min, Yuan

2009-01-01

Interference effects on the photoionization cross sections between two neighbouring atoms are considered based on the coherent scattering of the ionized electrons by the two nuclei when their separation is less than or comparable to the de Broglie wave length of the ionized electrons. As an example, the single atomic nitrogen ionization cross section and the total cross sections of two nitrogen atoms with coherently added photoionization amplitudes are calculated from the threshold to about 60 Å (1 Å = 0.1 nm) of the photon energy. The photoionization cross sections of atomic nitrogen are obtained by using the close-coupling R-matrix method. In the calculation 19 states are included. The ionization energy of the atomic nitrogen and the photoionization cross sections agree well with the experimental results. Based on the R-matrix results of atomic nitrogen, the interference effects between two neighbouring nitrogen atoms are obtained. It is shown that the interference effects are considerable when electrons are ionized just above the threshold, even for the separations between the two atoms are larger than two times of the bond length of N 2 molecules. Therefore, in hot and dense samples, effects caused by the coherent interference between the neighbours are expected to be observable for the total photoionization cross sections. (atomic and molecular physics)

Photoionization of the hydrogen atom in strong magnetic fields

Science.gov (United States)

Potekhin, Aleksandr IU.; Pavlov, George G.

1993-01-01

The photoionization of the hydrogen atom in magnetic fields B about 10 exp 11 - 10 exp 13 G typical of the surface layers of neutron stars is investigated analytically and numerically. We consider the photoionization from various tightly bound and hydrogen-like states of the atom for photons with arbitrary polarizations and wave-vector directions. It is shown that the length form of the interaction matrix elements is more appropriate in the adiabatic approximation than the velocity form, at least in the most important frequency range omega much less than omega(B), where omega(B) is the electron cyclotron frequency. Use of the length form yields nonzero cross sections for photon polarizations perpendicular to the magnetic field at omega less than omega(B); these cross sections are the ones that most strongly affect the properties of the radiation escaping from an optically thick medium, e.g., from the atmosphere of a neutron star. The results of the numerical calculations are fitted by simple analytical formulas.

Phase-resolved attosecond near-threshold photoionization of molecular nitrogen

International Nuclear Information System (INIS)

Haessler, S.; Ruchon, T.; Breger, P.; Carre, B.; Salieres, P.; Fabre, B.; Higuet, J.; Constant, E.; Mevel, E.; Mairesse, Y.; Caillat, J.; Maquet, A.; Taieeb, R.

2009-01-01

We photoionize nitrogen molecules with a train of extreme ultraviolet attosecond pulses together with a weak infrared field. We measure the phase of the two-color two-photon ionization transition (molecular phase) for different states of the ion. We observe a 0.9π shift for the electrons produced in the ionization channels leading to the X 2 Σ g + , v ' =1, and v ' =2 states. We relate this phase shift to the presence of a complex resonance in the continuum. By providing both a high spectral and temporal resolution, this general approach gives access to the evolution of extremely short-lived states, which is often not accessible otherwise.

Absolute photoionization cross sections of furanic fuels: 2-ethylfuran, 2-acetylfuran and furfural.

Science.gov (United States)

Smith, Audrey R; Meloni, Giovanni

2015-11-01

Absolute photoionization cross sections of the molecules 2-ethylfuran, 2-acetylfuran and furfural, including partial ionization cross sections for the dissociative ionized fragments, are measured for the first time. These measurements are important because they allow fuel quantification via photoionization mass spectrometry and the development of quantitative kinetic modeling for the complex combustion of potential fuels. The experiments are carried out using synchrotron photoionization mass spectrometry with an orthogonal time-of-flight spectrometer used for mass analysis at the Advanced Light Source of Lawrence Berkeley National Laboratory. The CBS-QB3 calculations of adiabatic ionization energies and appearance energies agree well with the experimental results. Several bond dissociation energies are also derived and presented. Copyright © 2015 John Wiley & Sons, Ltd.

Intershell correlations in photoionization of outer shells

Energy Technology Data Exchange (ETDEWEB)

Amusia, M.Ya. [The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904 (Israel); A.F. Ioffe Physical-Technical Institute, St. Petersburg 194021 (Russian Federation); Chernysheva, L.V. [A.F. Ioffe Physical-Technical Institute, St. Petersburg 194021 (Russian Federation); Drukarev, E.G. [National Research Center “Kurchatov Institute”, Konstantinov Petersburg Nuclear Physics Institute, St. Petersburg 188300 (Russian Federation)

2016-02-15

We demonstrate that the cross sections for photoionization of the outer shells are noticeably modified at the photon energies close to the thresholds of ionization of the inner shells due to correlations with the latter. The correlations may lead to increase or to decrease of the cross sections just above the ionization thresholds.

Intershell correlations in photoionization of outer shells

International Nuclear Information System (INIS)

Amusia, M.Ya.; Chernysheva, L.V.; Drukarev, E.G.

2016-01-01

We demonstrate that the cross sections for photoionization of the outer shells are noticeably modified at the photon energies close to the thresholds of ionization of the inner shells due to correlations with the latter. The correlations may lead to increase or to decrease of the cross sections just above the ionization thresholds.

Study of Photoionization and Fragmentation on CHClF2 : Experiments and Calculations

International Nuclear Information System (INIS)

Sheng, L.; Yang, B.; Huang, C.; Qi, F.; Zhang, Y.; Wang, Z.; Zhou, S.

2004-01-01

Full text: The photoionization and fragmentation of CHClF 2 are studied with VUV radiation and photoionization mass spectroscopy at NSRL. Ionization potential of Parent molecule CHClF 2 , appearance energies of some fragment ions, and dissociative energy of some fragmentation process are obtained from photoionization efficiency spectroscopy. Dissociative photoionization channels for formation of some fragment ions are proposed on comparison of determined appearance energies and energies predicted with Gaussian-98 calculation

Photoionization Modeling and the K Lines of Iron

Science.gov (United States)

Kallman, T. R.; Palmeri, P.; Bautista, M. A.; Mendoza, C.; Krolik, J. H.

2004-01-01

We calculate the efficiency of iron K line emission and iron K absorption in photoionized models using a new set of atomic data. These data are more comprehensive than those previously applied to the modeling of iron K lines from photoionized gases, and allow us to systematically examine the behavior of the properties of line emission and absorption as a function of the ionization parameter, density and column density of model constant density clouds. We show that, for example, the net fluorescence yield for the highly charged ions is sensitive to the level population distribution produced by photoionization, and these yields are generally smaller than those predicted assuming the population is according to statistical weight. We demonstrate that the effects of the many strongly damped resonances below the K ionization thresholds conspire to smear the edge, thereby potentially affecting the astrophysical interpretation of absorption features in the 7-9 keV energy band. We show that the centroid of the ensemble of K(alpha) lines, the K(beta) energy, and the ratio of the K(alpha(sub 1)) to K(alpha(sub 2)) components are all diagnostics of the ionization parameter of our model slabs.

Mass spectrometry. [review of techniques

Science.gov (United States)

Burlingame, A. L.; Kimble, B. J.; Derrick, P. J.

1976-01-01

Advances in mass spectrometry (MS) and its applications over the past decade are reviewed in depth, with annotated literature references. New instrumentation and techniques surveyed include: modulated-beam MS, chromatographic MS on-line computer techniques, digital computer-compatible quadrupole MS, selected ion monitoring (mass fragmentography), and computer-aided management of MS data and interpretation. Areas of application surveyed include: organic MS and electron impact MS, field ionization kinetics, appearance potentials, translational energy release, studies of metastable species, photoionization, calculations of molecular orbitals, chemical kinetics, field desorption MS, high pressure MS, ion cyclotron resonance, biochemistry, medical/clinical chemistry, pharmacology, and environmental chemistry and pollution studies.

2001 Gordon Research Conference on Photoions, Photoionization and Photodetachment. Final progress report [agenda and attendees list

International Nuclear Information System (INIS)

Johnson, Mark

2001-01-01

The Gordon Research Conference on Photoions, Photoionization and Photodetachment was held at Williams College, Williamstown, Massachusetts, July 8-13, 2001. The 72 conference attendees represented the spectrum of endeavor in this field, coming from academia, industry, and government laboratories, and including US and foreign scientists, senior researchers, young investigators, and students. Emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate discussion about the key issues in the field today. Time for formal presentations was limited. Sessions included the following topics: Vibrational structure, Time resolved studies: nuclear wavepackets, Valence photoionization, Clusters and networks, Resonance structures and decay mechanisms, Ultrafast photoionization, Threshold photoionization, Molecule fixed properties, and Collisional phenomena

Separation of uranium isotopes by selective photoionization

International Nuclear Information System (INIS)

Snavely, B.B.; Solarz, R.W.; Tuccio, S.A.

1975-01-01

Recent results of experiments on the laser photoseparation of U isotopes are reported. In the first series of experiments a two-step ionization process using a Xe laser to excite the atoms below the ionization level and then a Kr laser to ionize the atoms was described. Under the geometric conditions of the experiment and power of the Kr laser, enrichments between 2.5 and 3 percent were obtained in runs lasting 2 hrs. Calculations to describe the ion trajectories in the collector system reflected the two-band pattern observed on the Be collector plate. A system to study the photoionization process was assembled in which the U beam is excited to a desired energy level with a CW dye laser and an ultraviolet beam intercepts the excited U beam. An analysis of a photoionization spectrum obtained at a resolution of 8 A indicates that the peak cross section for transitions to autoionization states from the 7 M 7 level is large enough to be used in large-scale U separation systems. An ionization value of 6.15 +- 0.2 eV was deduced for the ionization potential of the U atom. (U.S.)

Electron-spin polarization of photoions produced through photoionization from the laser-excited triplet state of Sr

International Nuclear Information System (INIS)

Yonekura, Nobuaki; Nakajima, Takashi; Matsuo, Yukari; Kobayashi, Tohru; Fukuyama, Yoshimitsu

2004-01-01

We report the detailed experimental study on the production of electron-spin-polarized Sr + ions through one-photon resonant two-photon ionization via laser-excited 5s5p 3 P 1 (M J =+1) of Sr atoms produced by laser-ablation. We have experimentally confirmed that the use of laser-ablation for the production of Sr atoms prior to photoionization does not affect the electron-spin polarization. We have found that the degree of electron-spin polarization is 64±9%, which is in good agreement with our recent theoretical prediction. As we discuss in detail, we infer, from a simple analysis, that photoelectrons, being the counterpart of electron-spin-polarized Sr + ions, have approximately the same degree of electron-spin polarization. Our experimental results demonstrate that the combined use of laser-ablation technique and pulsed lasers for photoionization would be a compact and effective way to realize a pulsed source for spin-polarized ions and electrons for the studies of various spin-dependent dynamics in chemical physics

Runge-Lenz wave packet in multichannel Stark photoionization

International Nuclear Information System (INIS)

Texier, F.

2005-01-01

In a previous slow photoionization experiment, modulations of ionization rings were manifested for Xe in a constant electric field. The present quantum calculation reveals that the modulation is an effect of the multichannel core scattering and of tunneling waves through the Coulomb-Stark potential barrier: the barrier reduces the number of oscillations that is observed relatively to the number of oscillations of the short range wave functions, and the nonhydrogenic core phase shifts modify the position of the ionization rings. We find a hidden difference, in the ionization process, for two close values of the energy depending on the resonance with the barrier. The ionization intensity is interpreted as a Runge-Lenz wave packet; thus, we can relate the quantum modulation to the classical Coulomb-Stark trajectories. The Runge-Lenz wave packet differs from a usual temporal wave packet because its components are eigenstates of the Runge-Lenz vector z projection and its evolution is not temporal but spatial

Ionization photophysics and spectroscopy of cyanoacetylene

International Nuclear Information System (INIS)

Leach, Sydney; Champion, Norbert; Garcia, Gustavo A.; Fray, Nicolas; Gaie-Levrel, François; Mahjoub, Ahmed; Bénilan, Yves; Gazeau, Marie-Claire; Schwell, Martin

2014-01-01

Photoionization of cyanoacetylene was studied using synchrotron radiation over the non-dissociative ionization excitation range 11–15.6 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of cyanoacetylene was measured as 11.573 ± 0.010 eV. A detailed analysis of photoelectron spectra of HC 3 N involves new aspects and new assignments of the vibrational components to excitation of the A 2 Σ + and B 2 Π states of the cation. Some of the structured autoionization features observed in the 11.94 to 15.5 eV region of the total ion yield (TIY) spectrum were assigned to two Rydberg series converging to the B 2 Π state of HC 3 N + . A number of the measured TIY features are suggested to be vibrational components of Rydberg series converging to the C 2 Σ + state of HC 3 N + at ≈17.6 eV and others to valence shell transitions of cyanoacetylene in the 11.6–15 eV region. The results of quantum chemical calculations of the cation electronic state geometries, vibrational frequencies and energies, as well as of the C–H dissociation potential energy profiles of the ground and electronic excited states of the ion, are compared with experimental observations. Ionization quantum yields are evaluated and discussed and the problem of adequate calibration of photoionization cross-sections is raised

Polarization effects in above-threshold ionization with a mid-infrared strong laser field

Science.gov (United States)

Kang, Hui-Peng; Xu, Song-Po; Wang, Yan-Lan; Yu, Shao-Gang; Zhao, Xiao-Yun; Hao, Xiao-Lei; Lai, Xuan-Yang; Pfeifer, Thomas; Liu, Xiao-Jun; Chen, Jing; Cheng, Ya; Xu, Zhi-Zhan

2018-05-01

Using a semiclassical approach, we theoretically study the above-threshold ionization of magnesium by intense, mid-infrared laser pulses. The formation of low-energy structures in the photoelectron spectrum is found to be enhanced by comparing with a calculation based on the single-active electron approximation. By performing electron trajectory and recollision-time distribution analysis, we demonstrate that this phenomenon is due to the laser-induced ionic core polarization effects on the recolliding electrons. We also show that the polarization effects should be experimentally detectable. Our finding provides new insight into ultrafast control of strong-field photoionization and imaging of polar molecules.

Total absorption and photoionization cross sections of water vapor between 100 and 1000 A

Science.gov (United States)

Haddad, G. N.; Samson, J. A. R.

1986-01-01

Absolute photoabsorption and photoionization cross sections of water vapor are reported at a large number of discrete wavelengths between 100 and 1000 A with an estimate error of + or - 3 percent in regions free from any discrete structure. The double ionization chamber technique utilized is described. Recent calculations are shown to be in reasonable agreement with the present data.

Mass-Selective Laser Photoionization.

Science.gov (United States)

Smalley, R. E.

1982-01-01

Discusses the nature and applications of mass-selective laser photoionization. The ionization can be done with a single intense laser pulse lasting a few billionths of a second with no molecular fragmentation. Applications focus on: (1) benzene clusters, excimers, and exciplexes; (2) metal clusters; and (3) triplet formation and decay. (Author/JN)

A photoionization model for the optical line emission from cooling flows

Science.gov (United States)

Donahue, Megan; Voit, G. M.

1991-01-01

The detailed predictions of a photoionization model previously outlined in Voit and Donahue (1990) to explain the optical line emission associated with cooling flows in X-ray emitting clusters of galaxies are presented. In this model, EUV/soft X-ray radiation from condensing gas photoionizes clouds that have already cooled. The energetics and specific consequences of such a model, as compared to other models put forth in the literature is discussed. Also discussed are the consequences of magnetic fields and cloud-cloud shielding. The results illustrate how varying the individual column densities of the ionized clouds can reproduce the range of line ratios observed and strongly suggest that the emission-line nebulae are self-irradiated condensing regions at the centers of cooling flows.

Selective photoionization of gadolinium isotopes with a polarized laser

International Nuclear Information System (INIS)

Le Guyadec, E.

1990-06-01

The aim of this study is the use of gadolinium 157 as burnable poison in nuclear reactors. Spectroscopic isotopic displacements between Gd 156 and Gd 157 are low and the separation method studied is based on differentiated behavior, concerning polarized light, of even and odd gadolinium isotopes coming from their difference of nuclear spin. On this principle is based the simplest photoionization scheme. Selective ionization of odd isotopes is realized from the fundamental state with three resonating photons colinearly polarized. The experimental study confirms the possibility of efficient photoionization. The measured selectivity between Gd 157 and even isotope is over 48 in defined conditions because it can be destroyed by a magnetic field or if photons are not well polarized. Calculations and observations are in good agreement. Odd gadolinium isotope separation is feasible and effects preventing separation are evidenced [fr

Absolute photoionization cross sections of two cyclic ketones: cyclopentanone and cyclohexanone.

Science.gov (United States)

Price, Chelsea; Fathi, Yasmin; Meloni, Giovanni

2017-05-01

Absolute photoionization cross sections for cyclopentanone and cyclohexanone, as well as partial ionization cross sections for the dissociative ionized fragments, are presented in this investigation. Experiments are performed via a multiplexed photoionization mass spectrometer utilizing vacuum ultraviolet (VUV) synchrotron radiation supplied by the Advanced Light Source of Lawrence Berkeley National Laboratory. These results allow the quantification of these species that is relevant to investigate the kinetics and combustion reactions of potential biofuels. The CBS-QB3 calculated values for the adiabatic ionization energies agree well with the experimental values, and the identification of possible dissociative fragments is discussed for both systems. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.

Electron ionization and the Compton effect in double ionization of helium

International Nuclear Information System (INIS)

Samson, J.

1994-01-01

The author discusses ionization phenomena in helium, both photoionization and electron ionization. In particular he compares double ionization cross sections with total cross sections, as a function of electron energy, and photon energy. Data is discussed over the energy range up to 10 keV

Single- and multi-photon ionization studies of organosulfur species

Energy Technology Data Exchange (ETDEWEB)

Cheung, Yu -San [Iowa State Univ., Ames, IA (United States)

1999-02-12

Accurate ionization energies (IE`s) for molecular species are used for prediction of chemical reactivity and are of fundamental importance to chemists. The IE of a gaseous molecule can be determined routinely in a photoionization or a photoelectron experiment. IE determinations made in conventional photoionization and photoelectron studies have uncertainties in the range of 3--100 meV (25--250 cm^-1). In the past decade, the most exciting development in the field of photoionization and photoelectron spectroscopy has been the availability of high resolution, tunable ultraviolet (UV) and vacuum ultraviolet (VUV) laser sources. The laser pulsed field ionization photoelectron (PFI-PE) scheme is currently the state-of-the-art photoelectron spectroscopic technique and is capable of providing photoelectron energy resolution close to the optical resolution. The author has focused attention on the photoionization processes of some sulfur-containing species. The studies of the photoionization and photodissociation on sulfur-containing compounds [such as CS₂, CH₃SH, CH₃SSCH₃, CH₃CH₂SCH₂CH₃, HSCH₂CH₂SH and C₄H₄S (thiophene) and sulfur-containing radicals, such as HS, CS, CH₃S, CH₃CH₂S and CH₃SS], have been the major subjects in the group because sulfur is an important species contributing to air pollution in the atmosphere. The modeling of the combustion and oxidation of sulfur compounds represents important steps for the control of both the production and the elimination of sulfur-containing pollutants. Chapter 1 is a general introduction of the thesis. Chapters 2 and 6 contain five papers published in, or accepted for publication in, academic periodicals. In Chapter 7, the progress of the construction in the laboratory of a new vacuum ultraviolet laser system equipped with a reflectron mass

Ionization photophysics and spectroscopy of cyanoacetylene

Energy Technology Data Exchange (ETDEWEB)

Leach, Sydney; Champion, Norbert [LERMA UMR CNRS 8112, Observatoire de Paris-Meudon, 5 place Jules-Jansen, 92195 Meudon (France); Garcia, Gustavo A.; Fray, Nicolas; Gaie-Levrel, François [Synchrotron SOLEIL, L’Orme des Merisiers, St. Aubin, B.P. 48, 91192, Gif-sur-Yvette Cedex (France); Mahjoub, Ahmed; Bénilan, Yves; Gazeau, Marie-Claire; Schwell, Martin [LISA UMR CNRS 7583, Université Paris Est Créteil and Université Paris Diderot, Institut Pierre Simon Laplace, 61 Avenue du Général de Gaulle, 94010 Créteil (France)

2014-05-07

Photoionization of cyanoacetylene was studied using synchrotron radiation over the non-dissociative ionization excitation range 11–15.6 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of cyanoacetylene was measured as 11.573 ± 0.010 eV. A detailed analysis of photoelectron spectra of HC{sub 3}N involves new aspects and new assignments of the vibrational components to excitation of the A{sup 2}Σ{sup +} and B{sup 2}Π states of the cation. Some of the structured autoionization features observed in the 11.94 to 15.5 eV region of the total ion yield (TIY) spectrum were assigned to two Rydberg series converging to the B{sup 2}Π state of HC{sub 3}N{sup +}. A number of the measured TIY features are suggested to be vibrational components of Rydberg series converging to the C{sup 2}Σ{sup +} state of HC{sub 3}N{sup +} at ≈17.6 eV and others to valence shell transitions of cyanoacetylene in the 11.6–15 eV region. The results of quantum chemical calculations of the cation electronic state geometries, vibrational frequencies and energies, as well as of the C–H dissociation potential energy profiles of the ground and electronic excited states of the ion, are compared with experimental observations. Ionization quantum yields are evaluated and discussed and the problem of adequate calibration of photoionization cross-sections is raised.

Ionization processes in the Fe 27 region of hot iron plasma in the field of hard gamma radiation

International Nuclear Information System (INIS)

Illarionov, A.F.

1989-01-01

A highly ionized hot plasma of an iron 26 56 Fe-type heavy element in the field of hard ionizing gamma-ray radiation is considered. The processes of ionization and recombination are discussed for a plasma consisting of the fully ionized Fe 27 and the hydrogen-like Fe 26 ions of iron in the case of large optical depth of the plasma with respect to the photoionization by gamma-ray quanta. The self-ionization process of a hot plasma with the temperature kT ≅ I (I being the ionization potential), due to the production of the own ionizing gamma-ray quanta, by the free-free (ff) and recombination (fb) radiation mechanisms, is investigated. It is noted that in the stationary situation the process of self-ionization of a hot plasma imposes the restriction upon the plasma temperature, kT<1.5 I. It is shown that the ionization of heavy-ion plasma by the impact of thermal electrons is dominating over the processes of ff- and fb-selfionization of plasma only by the large concentration of hydrogen-like iron at the periphery of the region of fully ionized iron Fe 27

Photoionization cross section measurements of the excited states of cobalt in the near-threshold region

Directory of Open Access Journals (Sweden)

Xianfeng Zheng

2014-10-01

Full Text Available We present measurements of photoionization cross-sections of the excited states of cobalt using a two-color, two-step resonance ionization technique in conjunction with a molecular beam time of flight (TOF mass spectrometer. The atoms were produced by the laser vaporization of a cobalt rod, coupled with a supersonic gas jet. The absolute photoionization cross-sections at threshold and near-threshold regions (0-1.2 eV were measured, and the measured values ranged from 4.2±0.7 Mb to 10.5±1.8 Mb. The lifetimes of four odd parity energy levels are reported for the first time.

Study by photo-ionization of some simple poly-atomic molecules and calculation of the Franck-Condon factors; Etude par photo-ionization de quelques molecules poly-atomiques simples et calcul des facteurs de Franck-Condon

Energy Technology Data Exchange (ETDEWEB)

Botter, R [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1968-02-01

The photo-ionization yield curves for C{sub 2}H{sub 2}, C{sub 2}D{sub 2}, C{sub 2}H{sub 4} and C{sub 2}H{sub 2}D{sub 2} have been determined using a mass spectrometer coupled with an U.V. monochromator. Besides exhibiting a stair case structure near threshold due to the excitation of vibrational levels in the ion ground state, all the curves have broad maxima corresponding to auto-ionization phenomena. The ionization potentials of these molecules have been measured, together with the appearance potentials of the main ion-fragments. The excitation probabilities for the vibrational levels during ionization, or Franck-Condon factors, have been calculated for C{sub 2}H{sub 2} and C{sub 2}D{sub 2} using the method developed by Sharp and Rosenstock. Good agreement is generally obtained between the calculated values and those obtained experimentally from the photo-ionization yield curves. The preceding calculation method is then extended to the case where the electronic transition occurs with changes in the geometrical structure of the molecule (in particular, changes of symmetry). The Franck-Condon factors have been determined for NH{sub 3} (symmetry changes) and for H{sub 2}O (changes in the equilibrium angle). Calculations show that there is generally considerable excitation of the combination bands. (author) [French] Les courbes de rendement de photoionisation pour C{sub 2}H{sub 2}, C{sub 2}D{sub 2}, C{sub 2}H{sub 4} et C{sub 2}H{sub 2}D{sub 2} determinees a l'aide d'un spectrometre de masse auquel etait couple un monochromateur U.V. En plus d'une structure en escalier au voisinage du seuil, due a l'excitation de niveaux vibrationnels dans l'ion a l'etat fondamental, toutes les courbes presentent des maxima tres aplatis correspondant a des phenomenes d'auto-ionisation. Les potentiels d'ionisation de ces molecules ont ete mesures ainsi que les potentiels d'apparition des principaux ions fragments. Les probabilites d'excitation de niveaux de vibration au cours de l

Terahertz radiation driven by two-color laser pulses at near-relativistic intensities: Competition between photoionization and wakefield effects

Science.gov (United States)

González de Alaiza Martínez, P.; Davoine, X.; Debayle, A.; Gremillet, L.; Bergé, L.

2016-01-01

We numerically investigate terahertz (THz) pulse generation by linearly-polarized, two-color femtosecond laser pulses in highly-ionized argon. Major processes consist of tunneling photoionization and ponderomotive forces associated with transverse and longitudinal field excitations. By means of two-dimensional particle-in-cell (PIC) simulations, we reveal the importance of photocurrent mechanisms besides transverse and longitudinal plasma waves for laser intensities >1015 W/cm2. We demonstrate the following. (i) With two-color pulses, photoionization prevails in the generation of GV/m THz fields up to 1017 W/cm2 laser intensities and suddenly loses efficiency near the relativistic threshold, as the outermost electron shell of ionized Ar atoms has been fully depleted. (ii) PIC results can be explained by a one-dimensional Maxwell-fluid model and its semi-analytical solutions, offering the first unified description of the main THz sources created in plasmas. (iii) The THz power emitted outside the plasma channel mostly originates from the transverse currents. PMID:27255689

Synthetic oligomer analysis using atmospheric pressure photoionization mass spectrometry at different photon energies

International Nuclear Information System (INIS)

Desmazières, Bernard; Legros, Véronique; Giuliani, Alexandre; Buchmann, William

2014-01-01

Graphical abstract: Atmospheric pressure photoIonization mass spectra of synthetic oligomers were recorded in the negative mode by varying the photon energy using synchrotron radiation. Photon energy required for an efficient ionization of the polymer was correlated to ionization potential of the solvent (for example 9.4 eV for tetrahydrofuran). -- Highlights: •Atmospheric pressure photoionization was performed using synchrotron radiation. •Photoionization of oligomers in THF with 10% CH 2 Cl 2 produces intact [M + Cl] − ions. •The photon energy required corresponds to ionization potential of the solvent. •Polymer distributions depend on source parameters such T °C and applied voltages. •Liquid chromatography was coupled to MS using an APPI interface for polymer analysis. -- Abstract: Atmospheric pressure photoionization (APPI) followed by mass spectrometric detection was used to ionize a variety of polymers: polyethylene glycol, polymethyl methacrylate, polystyrene, and polysiloxane. In most cases, whatever the polymer or the solvent used (dichloromethane, tetrahydrofuran, hexane, acetone or toluene), only negative ion mode produced intact ions such as chlorinated adducts, with no or few fragmentations, in contrast to the positive ion mode that frequently led to important in-source fragmentations. In addition, it was shown that optimal detection of polymer distributions require a fine tuning of other source parameters such as temperature and ion transfer voltage. Series of mass spectra were recorded in the negative mode, in various solvents (dichloromethane, tetrahydrofuran, hexane, toluene, and acetone), by varying the photon energy from 8 eV up to 10.6 eV using synchrotron radiation. To these solvents, addition of a classical APPI dopant (toluene or acetone) was not necessary. Courtesy of the synchrotron radiation, it was demonstrated that the photon energy required for an efficient ionization of the polymer was correlated to the ionization energy

Synthetic oligomer analysis using atmospheric pressure photoionization mass spectrometry at different photon energies

Energy Technology Data Exchange (ETDEWEB)

Desmazières, Bernard [Global Bioenergies, 5 rue Henri Desbruyeres, 91030 Evry (France); Legros, Véronique [CNRS, UMR8587, Université d’Evry-Val-d’Essonne, Laboratoire Analyse et Modélisation pour la Biologie et l’Environnement, F-91025 Evry (France); Giuliani, Alexandre [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette (France); UAR1008, CEPIA, INRA, Rue de la Geraudiere, F-44316 Nantes (France); Buchmann, William, E-mail: william.buchmann@univ-evry.fr [CNRS, UMR8587, Université d’Evry-Val-d’Essonne, Laboratoire Analyse et Modélisation pour la Biologie et l’Environnement, F-91025 Evry (France)

2014-01-15

Graphical abstract: Atmospheric pressure photoIonization mass spectra of synthetic oligomers were recorded in the negative mode by varying the photon energy using synchrotron radiation. Photon energy required for an efficient ionization of the polymer was correlated to ionization potential of the solvent (for example 9.4 eV for tetrahydrofuran). -- Highlights: •Atmospheric pressure photoionization was performed using synchrotron radiation. •Photoionization of oligomers in THF with 10% CH{sub 2}Cl{sub 2} produces intact [M + Cl]{sup −} ions. •The photon energy required corresponds to ionization potential of the solvent. •Polymer distributions depend on source parameters such T °C and applied voltages. •Liquid chromatography was coupled to MS using an APPI interface for polymer analysis. -- Abstract: Atmospheric pressure photoionization (APPI) followed by mass spectrometric detection was used to ionize a variety of polymers: polyethylene glycol, polymethyl methacrylate, polystyrene, and polysiloxane. In most cases, whatever the polymer or the solvent used (dichloromethane, tetrahydrofuran, hexane, acetone or toluene), only negative ion mode produced intact ions such as chlorinated adducts, with no or few fragmentations, in contrast to the positive ion mode that frequently led to important in-source fragmentations. In addition, it was shown that optimal detection of polymer distributions require a fine tuning of other source parameters such as temperature and ion transfer voltage. Series of mass spectra were recorded in the negative mode, in various solvents (dichloromethane, tetrahydrofuran, hexane, toluene, and acetone), by varying the photon energy from 8 eV up to 10.6 eV using synchrotron radiation. To these solvents, addition of a classical APPI dopant (toluene or acetone) was not necessary. Courtesy of the synchrotron radiation, it was demonstrated that the photon energy required for an efficient ionization of the polymer was correlated to the

Investigation on the absolute and relative photoionization cross sections of 3 potential propargylic fuels.

Science.gov (United States)

Winfough, Matthew; Meloni, Giovanni

2017-12-01

Absolute photoionization cross sections for 2 potential propargylic fuels (propargylamine and dipropargyl ether) along with the partial ionization cross sections for their dissociative fragments are measured and presented for the first time via synchrotron photoionization mass spectrometry. The experimental setup consists of a multiplexed orthogonal time-of-flight mass spectrometer and is located at the Advanced Light Source facility of the Lawrence Berkeley National Laboratory in Berkeley, California. Data for a third propargylic compound (propargyl alcohol) were taken; however, because of its low signal, due to its weakly bound cation, only the dissociative ionization fragment from the H-loss channel is observed and presented. Suggested pathways leading to formation of dissociative photoionization fragments along with CBS-QB3 calculated adiabatic ionization energies and appearance energies for the dissociative fragments are also presented. Copyright © 2017 John Wiley & Sons, Ltd.

Solid-Phase Microextraction Coupled to Capillary Atmospheric Pressure Photoionization-Mass Spectrometry for Direct Analysis of Polar and Nonpolar Compounds.

Science.gov (United States)

Mirabelli, Mario F; Zenobi, Renato

2018-04-17

A novel capillary ionization source based on atmospheric pressure photoionization (cAPPI) was developed and used for the direct interfacing between solid-phase microextraction (SPME) and mass spectrometry (MS). The efficiency of the source was evaluated for direct and dopant-assisted photoionization, analyzing both polar (e.g., triazines and organophosphorus pesticides) and nonpolar (polycyclic aromatic hydrocarbons, PAHs) compounds. The results show that the range of compound polarity, which can be addressed by direct SPME-MS can be substantially extended by using cAPPI, compared to other sensitive techniques like direct analysis in real time (DART) and dielectric barrier discharge ionization (DBDI). The new source delivers a very high sensitivity, down to sub parts-per-trillion (ppt), making it a viable alternative when compared to previously reported and less comprehensive direct approaches.

K-shell ionization and double-ionization of Au atoms with 1.33 MeV photons

International Nuclear Information System (INIS)

Belkacem, A.; Dauvergne, D.; Feinberg, B.; Ionescu, D.; Maddi, J.; Sorensen, A.H.

2000-01-01

At relativistic energies, the cross section for the atomic photoelectric effect drops off as does the cross section for liberating any bound electron through Compton scattering. However, when the photon energy exceeds twice the rest mass of the electron, ionization may proceed via electron-positron pair creation. We used 1.33 MeV photons impinging on Au thin foils to study double K-shell ionization and vacuum-assisted photoionization. The preliminary results yield a ratio of vacuum-assisted photoionization and pair creation of 2x10 -3 , a value that is substantially higher than the ratio of photo double ionization to single photoionization that is found to be 0.5-1x10 -4 . Because of the difficulties and large error bars associated with the small cross sections additional measurements are needed to minimize systematic errors

Fluorescence excitation studies of molecular photoionization in external electric fields

International Nuclear Information System (INIS)

Poliakoff, E.D.; Dehmer, J.L.; Parr, A.C.; Leroi, G.E.

1985-01-01

Using molecular nitrogen as an example, we show that fluorescence excitation spectroscopy can be used to measure partial photoionization cross sections of free molecules in external electric fields. The production of the N 2 + (B 2 Σ/sub u/ + ) state was studied and the threshold for this process was found to shift linearly with the square root of the applied field. This behavior is compared with the hydrogenic case and with previously studied systems

Resonances in photoionization. Cross section for vibrationally excited H2

International Nuclear Information System (INIS)

Mezei, J.Zs.; Jungen, Ch.

2011-01-01

Complete text of publication follows. Diatomic molecular Hydrogen is the most abundant molecule in interstellar molecular clouds. The modeling of these environments relies on accurate cross sections for the various relevant processes. Among them, the photoionization plays a major role in the kinetics and in the energy exchanges involving H 2 . The recent discovery of vibrationally excited molecular hydrogen in extragalactic environments revealed the need for accurate evaluation of the corresponding photoionization cross sections. In the present work we report theoretical photoionization cross sections for excitation from excited vibrational levels of the ground state, dealing with the Q(N = 1) (ΔN = 0, where N is the total angular momentum of the molecule) transitions which account for roughly one third of the total photoabsorption cross section. We will focus on the v' = 1 excited level of the ground electronic state. Our calculations are based on Multichannel Quantum Defect Theory (MQDT), which allows us to take into account of the full manifold of Rydberg states and their interactions with the electronic continuum. We have carried out two types of MQDT calculations. First, we omitted all open channels and calculated energy levels, wave functions and spontaneous emission Einstein coefficients, making use of the theoretical method presented in [2]. In a second set of calculations we included the open ionization channels in the computations getting the continuum phase shifts, channel mixing coefficients and channel dipole moments and finally the photoabsorption/ photoionization cross section. The cross section is dominated by the presence of resonance structures corresponding to excitation of various vibrational levels of bound electronic states which lie above the ionization threshold. In order to assess the importance of the resonances we have calculated for each vibrational interval (the energy interval between two consecutive ionization thresholds) the

Double-continuum wave functions and double-photoionization cross sections of two-electron systems

International Nuclear Information System (INIS)

Tiwary, S.N.

1996-09-01

The present review briefly presents the growing experimental as well as theoretical interests in recent years in the double-continuum wave functions and double-photoionization cross sections of two-electron systems. The validity of existing double-continuum wave functions is analyzed and the importance of electronic correlations in both the initial as well as final states wave functions involved in the transition amplitude for double-photoionization process is demonstrated. At present, we do not have comprehensive and practical double-continuum wave functions which account the full correlation of two-electron in the continuum. Basic difficulties in making accurate theoretical calculations of double ionization by a single high energy photon especially in the vicinity of the threshold, where the correlation plays an important role, are discussed. Illuminating, illustrative and representative examples are presented in order to show the present status and the progress in this field. Future challenges and directions, in high-precision double-photoionization cross sections calculations, have been discussed and suggested. (author). 133 refs, 9 figs

Photoionization of sodium atoms and electron scattering from ionized sodium

Science.gov (United States)

Dasgupta, A.; Bhatia, A. K.

1985-01-01

The polarized-orbital method of Temkin (1957) is applied using polarized orbitals determined from Sternheimer's equation to compute the photoionization cross sections of Na atoms from threshold to about 60 eV. The approximations involved in the analysis are explained in detail; the explicit forms of the integrals and matrix expressions are given in appendices; and the results are presented in tables and graphs. Good agreement is found with the results of Chang and Kelly (1975), and the possibility that small amounts of molecular vapor in Na-photoionization experiments are responsible for the discrepancies between calculated and measured cross sections is considered.

Photoionization of Ar2 at high resolution

International Nuclear Information System (INIS)

Dehmer, P.M.

1982-01-01

The relative photoionization cross section of Ar 2 was determined at a resolution of 0.07 A in the wavelength region from 800 to 850 A using a new photoionization mass spectrometer that combines a high intensity helium continuum lamp with a free supersonic molecular beam source. In the region studied, the photoionization cross section is dominated by autoionization of molecular Rydberg states, and the structure is diffuse owing to the combined effects of autoionization and predissociation. The molecular photoionization spectrum is extremely complex and shows little resemblence either to the corresponding atomic spectrum (indicating that the spectrum of the dimer is not simply a perturbed atomic spectrum) or to the molecular absorption spectrum at longer wavelengths. The regular vibrational progressions seen at longer wavelengths are absent above the first ionization potential. Detailed spectroscopic analysis is possible for only a small fraction of the observed features; however, vibrational intervals of 50--100 cm -1 suggest that some of the Rydberg states have B 2 Pi/sub 3/2g/ ionic cores. A comparison of the absorption and photoionization spectra shows that, at wavelengths shorter than approx.835 A, many of the excited states decay via mechanisms other than autoionization

Theory of attosecond delays in molecular photoionization.

Science.gov (United States)

Baykusheva, Denitsa; Wörner, Hans Jakob

2017-03-28

We present a theoretical formalism for the calculation of attosecond delays in molecular photoionization. It is shown how delays relevant to one-photon-ionization, also known as Eisenbud-Wigner-Smith delays, can be obtained from the complex dipole matrix elements provided by molecular quantum scattering theory. These results are used to derive formulae for the delays measured by two-photon attosecond interferometry based on an attosecond pulse train and a dressing femtosecond infrared pulse. These effective delays are first expressed in the molecular frame where maximal information about the molecular photoionization dynamics is available. The effects of averaging over the emission direction of the electron and the molecular orientation are introduced analytically. We illustrate this general formalism for the case of two polyatomic molecules. N 2 O serves as an example of a polar linear molecule characterized by complex photoionization dynamics resulting from the presence of molecular shape resonances. H 2 O illustrates the case of a non-linear molecule with comparably simple photoionization dynamics resulting from a flat continuum. Our theory establishes the foundation for interpreting measurements of the photoionization dynamics of all molecules by attosecond metrology.

EMISSION SPECTRUM OF HELIUM-LIKE IONS IN PHOTOIONIZED PLASMAS

International Nuclear Information System (INIS)

Wang, Feilu; Salzmann, David; Zhao, Gang; Takabe, Hideaki

2012-01-01

The aim of the present paper is to investigate the influence of inner-shell photoionization and photoexcitation on He α and its satellite's spectra in photoionized plasmas. An analysis is carried out on the relative importance of the various atomic processes in photoionized plasmas as a function of the electron temperature and irradiation conditions. In particular, we investigate the influence of K-shell photoionization of Li-like ions on the He α spectrum and of Be-like ions on the He α satellites. It is found that in photoionized plasmas these inner-shell processes contribute significantly under low radiation temperature and/or intensity, when Li- and Be-like ions are highly abundant but highly ionized H-like ions are rare. A short discussion is presented about the parameter space in which the excited 1s2p state has statistical or non-statistical distributions, and how such distributions affect the emission spectrum.

Photoionization of Li and Na in Debye plasma environments

International Nuclear Information System (INIS)

Sahoo, Satyabrata; Ho, Y.K.

2006-01-01

A calculation of the photoionization cross sections is presented for alkali-metal atoms such as Li and Na in plasma environments. The computational scheme is based on the complex coordinate rotation method. A model potential formalism has been used to simplify the computational complexity of the problems of making quantitative predictions of properties and interactions of many electron systems in Debye plasmas. The plasma environment is found to appreciably influence the photoionization cross sections. In this regard the photoionization cross sections of isolated atoms are also discussed that is found to be in good agreement with the previous theoretical results. It is observed that the strong plasma screening effect remarkably alters the photoionization cross sections near the ionization threshold. The Cooper minimum in the photoionization cross sections of Na shifts toward the higher energy as the plasma screening effect increases. For Li, the Cooper minimum is uncovered in strong plasma environments. This is the first time such structures have been determined

A VUV photoionization organic aerosol mass spectrometric study with synchrotron radiation

Energy Technology Data Exchange (ETDEWEB)

Fang Wenzheng; Lei Gong; Shan Xiaobin; Liu Fuyi [School of Nuclear Science and Technology, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Anhui, Hefei 230029 (China); Wang Zhenya [Laboratory of Environmental Spectroscopy, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031 (China); Sheng Liusi, E-mail: lssheng@ustc.edu.cn [School of Nuclear Science and Technology, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Anhui, Hefei 230029 (China)

2011-04-15

Research highlights: {yields} A photoionization aerosol time-of-flight mass spectrometer (ATOFMS) has been developed for on-line analysis of organic compounds in aerosol particles using tunable vacuum ultraviolet (VUV) synchrotron radiation. {yields} The degree of fragmentation of molecule can be controlled either by the heater temperature or by the photon energy. {yields} The direct determination of the IEs of benzopheneone (9.07 eV), salicylic acid (8.72 eV), and urea (9.85 eV) are measured from the photoionization efficiency spectra. {yields} The species can be identified by their molecular and fragment ions weights as well as by the comparisions between their theoretical and experimental ionization energies. - Abstract: A photoionization aerosol time-of-flight mass spectrometer (ATOFMS) has been developed for on-line analysis of organic compounds in aerosol particles using tunable vacuum ultraviolet (VUV) synchrotron radiation. Aerosol particles can be sampled directly from atmospheric pressure and are focused through an aerodynamic lens assembly into the mass spectrometer. The particles are vaporized when they impact on a heater, and then the nascent vapor is softly photoionized by synchrotron radiation. The degree of fragmentation of molecule can be controlled either by the heater temperature or by the photon energy. Thus, fragment-free tunable VUV mass spectra are obtained by tuning the photon energy close to the ionization energies (IEs) of the sample molecules. The direct determination of the IEs of benzophenone (9.07 eV), salicylic acid (8.72 eV), and urea (9.85 eV) are measured from the photoionization efficiency spectra with uncertainties of {+-}50 meV. Ab initio calculations have been employed to predict the theoretical ionization energy.

Multiple photoionization following 3d5/2-shell threshold ionization of

International Nuclear Information System (INIS)

Matsui, T; Yoshii, H; Tsukamoto, K; Kawakita, S; Murakami, E; Adachi, J; Yagishita, A; Morioka, Y; Hayaishi, T

2004-01-01

Multiple photoionization of Xe near the 3d 5/2 -shell threshold photoionization region is studied by threshold electron-ion coincidence spectroscopy. The coincidence spectra of Xe 3+ to Xe 7+ ions exhibit characteristic profiles associated with multi-step post-collision interactions in Auger cascades following 3d 5/2 -shell threshold photoionization. The Auger cascade decay channels leading to the formation of multiply charged ions are deduced from the energies of the profile peaks, which increase gradually with increasing charge state. The formation of Xe 3+ to Xe 5+ ions is found to arise from cascades of normal Auger decays, whereas the formation of Xe 6+ and Xe 7+ ions involves double Auger decays. The branching ratio of double to normal Auger decays is estimated to be 0.25 (±0.1) for the decays following the creation of 3d 5/2 -hole states in Xe

Ionization in matrix-assisted laser desorption/ionization: singly charged molecular ions are the lucky survivors.

Science.gov (United States)

Karas, M; Glückmann, M; Schäfer, J

2000-01-01

A new model for the ionization processes in UV matrix-assisted laser desorption/ionization (MALDI) which accounts for the major phenomena observed is presented and discussed. The model retains elements of earlier approaches, such as photoionization and photochemical reactions, but it redefines these in the light of new working questions, most importantly why only singly charged ions are detected. Based on experimental evidence, the formation of singly and multiply charged clusters by a deficiency/excess of ions and also by photoionization and subsequent photochemical processes is pointed out to be the major ionization processes, which typically occur in parallel. The generation of electrons and their partial loss into the surrounding vacuum and solid, on the one hand, results in a positively charged ion-neutral plume facilitating a high overall ionization yield. On the other hand, these electrons, and also the large excess of protonated matrix ions in the negative ion mode, induce effective ion reneutralization in the plume. These neutralization processes are most effective for the highly charged cluster ions initially formed. Their fragmentation behaviour is evidenced in fast metastable fragmentation characteristics and agrees well with an electron capture dissociation mechanism and the enthalpy transfer upon neutralization forms the rationale for the prominent fragmentation and intense chemical noise accompanying successful MALDI. Within the course of the paper, cross-correlations with other desorption/ionization techniques and with earlier discussions on their mechanisms are drawn. Copyright 2000 John Wiley & Sons, Ltd.

Field ionization mass spectrometry (FIMS) applied to tracer studies and isotope dilution analysis

International Nuclear Information System (INIS)

Anbar, M.; Heck, H.d'A.; McReynolds, J.H.; St John, G.A.

1975-01-01

The nonfragmenting nature of field ionization mass spectrometry makes it a preferred technique for the isotopic analysis of multilabeled organic compounds. The possibility of field ionization of nonvolatile thermolabile materials significantly extends the potential uses of this technique beyond those of conventional ionization methods. Multilabeled tracers may be studied in biological systems with a sensitivity comparable to that of radioactive tracers. Isotope dilution analysis may be performed reliably by this technique down to picogram levels. These techniques will be illustrated by a number of current studies using multilabeled metabolites and drugs. The scope and limitations of the methodology are discussed

Plasma production via field ionization

Directory of Open Access Journals (Sweden)

C. L. O’Connell

2006-10-01

Full Text Available Plasma production via field ionization occurs when an incoming particle beam is sufficiently dense that the electric field associated with the beam ionizes a neutral vapor or gas. Experiments conducted at the Stanford Linear Accelerator Center explore the threshold conditions necessary to induce field ionization by an electron beam in a neutral lithium vapor. By independently varying the transverse beam size, number of electrons per bunch, or bunch length, the radial component of the electric field is controlled to be above or below the threshold for field ionization. Additional experiments ionized neutral xenon and neutral nitric oxide by varying the incoming beam’s bunch length. A self-ionized plasma is an essential step for the viability of plasma-based accelerators for future high-energy experiments.

Photoionization microscopy of hydrogen atom near a metal surface

International Nuclear Information System (INIS)

Yang Hai-Feng; Wang Lei; Liu Xiao-Jun; Liu Hong-Ping

2011-01-01

We have studied the ionization of Rydberg hydrogen atom near a metal surface with a semiclassical analysis of photoionization microscopy. Interference patterns of the electron radial distribution are calculated at different scaled energies above the classical saddle point and at various atom—surface distances. We find that different types of trajectories contribute predominantly to different manifolds in a certain interference pattern. As the scaled energy increases, the structure of the interference pattern evolves smoothly and more types of trajectories emerge. As the atom approaches the metal surface closer, there are more types of trajectories contributing to the interference pattern as well. When the Rydberg atom comes very close to the metal surface or the scaled energy approaches the zero field ionization energy, the potential induced by the metal surface will make atomic system chaotic. The results also show that atoms near a metal surface exhibit similar properties like the atoms in the parallel electric and magnetic fields. (atomic and molecular physics)

Ionization front accelerator

International Nuclear Information System (INIS)

Olson, C.L.

1975-01-01

In a recently proposed linear collective accelerator, ions are accelerated in a steep, moving potential well created at the head of an intense relativistic electron beam. The steepness of the potential well and its motion are controlled by the external ionization of a suitable background gas. Calculations concerning optimum choices for the background gas and the ionization method are presented; a two-step photoionization process employing Cs vapor is proposed. In this process, a super-radiant light source is used to excite the gas, and a UV laser is used to photoionize the excited state. The appropriate line widths and coupled ionization growth rate equations are discussed. Parameter estimates are given for a feasibility experiment, for a 1 GeV proton accelerator, and for a heavy ion accelerator (50 MeV/nucleon uranium). (auth)

Laboratory Photoionization Fronts in Nitrogen Gas: A Numerical Feasibility and Parameter Study

Science.gov (United States)

Gray, William J.; Keiter, P. A.; Lefevre, H.; Patterson, C. R.; Davis, J. S.; van Der Holst, B.; Powell, K. G.; Drake, R. P.

2018-05-01

Photoionization fronts play a dominant role in many astrophysical situations but remain difficult to achieve in a laboratory experiment. We present the results from a computational parameter study evaluating the feasibility of the photoionization experiment presented in the design paper by Drake et al. in which a photoionization front is generated in a nitrogen medium. The nitrogen gas density and the Planckian radiation temperature of the X-ray source define each simulation. Simulations modeled experiments in which the X-ray flux is generated by a laser-heated gold foil, suitable for experiments using many kJ of laser energy, and experiments in which the flux is generated by a “z-pinch” device, which implodes a cylindrical shell of conducting wires. The models are run using CRASH, our block-adaptive-mesh code for multimaterial radiation hydrodynamics. The radiative transfer model uses multigroup, flux-limited diffusion with 30 radiation groups. In addition, electron heat conduction is modeled using a single-group, flux-limited diffusion. In the theory, a photoionization front can exist only when the ratios of the electron recombination rate to the photoionization rate and the electron-impact ionization rate to the recombination rate lie in certain ranges. These ratios are computed for several ionization states of nitrogen. Photoionization fronts are found to exist for laser-driven models with moderate nitrogen densities (∼1021 cm‑3) and radiation temperatures above 90 eV. For “z-pinch”-driven models, lower nitrogen densities are preferred (<1021 cm‑3). We conclude that the proposed experiments are likely to generate photoionization fronts.

Infrared laser ablation atmospheric pressure photoionization mass spectrometry.

Science.gov (United States)

Vaikkinen, Anu; Shrestha, Bindesh; Kauppila, Tiina J; Vertes, Akos; Kostiainen, Risto

2012-02-07

In this paper we introduce laser ablation atmospheric pressure photoionization (LAAPPI), a novel atmospheric pressure ion source for mass spectrometry. In LAAPPI the analytes are ablated from water-rich solid samples or from aqueous solutions with an infrared (IR) laser running at 2.94 μm wavelength. Approximately 12 mm above the sample surface, the ablation plume is intercepted with an orthogonal hot solvent (e.g., toluene or anisole) jet, which is generated by a heated nebulizer microchip and directed toward the mass spectrometer inlet. The ablated analytes are desolvated and ionized in the gas-phase by atmospheric pressure photoionization using a 10 eV vacuum ultraviolet krypton discharge lamp. The effect of operational parameters and spray solvent on the performance of LAAPPI is studied. LAAPPI offers ~300 μm lateral resolution comparable to, e.g., matrix-assisted laser desorption ionization. In addition to polar compounds, LAAPPI efficiently ionizes neutral and nonpolar compounds. The bioanalytical application of the method is demonstrated by the direct LAAPPI analysis of rat brain tissue sections and sour orange (Citrus aurantium) leaves. © 2012 American Chemical Society

Characterization of combustion-generated carbonaceous nanoparticles by size-dependent ultraviolet laser photoionization.

Science.gov (United States)

Commodo, Mario; Sgro, Lee Anne; Minutolo, Patrizia; D'Anna, Andrea

2013-05-16

Photoelectric charging of particles is a powerful tool for online characterization of submicrometer aerosol particles. Indeed photoionization based techniques have high sensitivity and chemical selectivity. Moreover, they yield information on electronic properties of the material and are sensitive to the state of the surface. In the present study the photoionization charging efficiency, i.e., the ratio between the generated positive ions and the corresponding neutral ones, for different classes of flame-generated carbonaceous nanoparticles was measured. The fifth harmonics of a Nd:YAG laser, 213 nm (5.82 eV), was used as an ionization source for the combustion generated nanoparticles, whereas a differential mobility analyzer (DMA) coupled to a Faraday cup electrometer was used for particle classification and detection. Carbonaceous nanoparticles in the nucleation mode, i.e., sizes ranging from 1 to 10 nm, show a photoionization charging efficiency clearly dependent on the flame conditions. In particular, we observed that the richer the flame is, i.e., the higher the equivalent ratio is, the higher the photon charging efficiency is. We hypothesized that such an increase in the photoionization propensity of the carbonaceous nanoparticles from richer flame condition is associated to the presence within the particles of larger aromatic moieties. The results clearly show that photoionization is a powerful diagnostic tool for the physical-chemical characterization of combustion aerosol, and it may lead to further insights into the soot formation mechanism.

Absolute photoionization cross sections of atomic oxygen

Science.gov (United States)

Samson, J. A. R.; Pareek, P. N.

1985-01-01

The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.

Ultrapressure liquid chromatography-tandem mass spectrometry assay using atmospheric pressure photoionization (UPLC-APPI-MS/MS) for quantification of 4-methoxydiphenylmethane in pharmacokinetic evaluation.

Science.gov (United States)

Farhan, Nashid; Fitzpatrick, Sean; Shim, Yun M; Paige, Mikell; Chow, Diana Shu-Lian

2016-09-05

4-Methoxydiphenylmethane (4-MDM), a selective augmenter of Leukotriene A4 Hydrolase (LTA4H), is a new anti-inflammatory compound for potential treatment of chronic obstructive pulmonary disease (COPD). Currently, there is no liquid chromatography tandem mass spectrometric (LC-MS/MS) method for the quantification of 4-MDM. A major barrier for developing the LC-MS/MS method is the inability of electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) to ionize 4-MDM due to its hydrophobicity and lack of any functional group for ionization. With the advent of atmospheric pressure photoionization (APPI) technique, many hydrophobic compounds have been demonstrated to ionize by charge transfer reactions. In this study, a highly sensitive ultrapressure liquid chromatography tandem mass spectrometry assay using atmospheric pressure photoionization (UPLC-APPI-MS/MS) for the quantifications of 4-MDM in rat plasma has been developed and validated. 4-MDM was extracted from the plasma by solid phase extraction (SPE) and separated chromatographically using a reverse phase C8 column. The photoionization (PI) was achieved by introducing anisole as a dopant to promote the reaction of charge transfer. The assay with a linear range of 5 (LLOQ)-400ngmL(-1) met the regulatory requirements for accuracy, precision and stability. The validated assay was employed to quantify the plasma concentrations of 4-MDM after an oral dosing in Sprague Dawley (SD) rats. Copyright © 2016 Elsevier B.V. All rights reserved.

Photoionization dynamics of excited Ne, Ar, Kr and Xe atoms near threshold

International Nuclear Information System (INIS)

Sukhorukov, V L; Petrov, I D; Schäfer, M; Merkt, F; Ruf, M-W; Hotop, H

2012-01-01

A review of experimental and theoretical studies of the threshold photoionization of the heavier rare-gas atoms is presented, with particular emphasis on the autoionization resonances in the spectral region between the lowest two ionization thresholds 2 P 3/2 and 2 P 1/2 , accessed from the ground or excited states. Observed trends in the positions, widths and shapes of the autoionization resonances depending on the atomic number, the principal quantum number n, the orbital angular momentum quantum number ℓ and further quantum numbers specifying the fine- and hyperfine-structure levels are summarized and discussed in the light of ab initio and multichannel quantum defect theory calculations. The dependence of the photoionization spectra on the initially prepared neutral state are also discussed, including results on the photoionization cross sections and photoelectron angular distributions of polarized excited states. The effects of various approximations in the theoretical treatment of photoionization in these systems are analysed. The very large diversity of observed phenomena and the numerous anomalies in spectral structures associated with the threshold ionization of the rare-gas atoms can be described in terms of a limited set of interactions and dynamical processes. Examples are provided illustrating characteristic aspects of the photoionization, and sets of recommended parameters describing the energy-level structure and photoionization dynamics of the rare-gas atoms are presented which were extracted in a critical analysis of the very large body of experimental and theoretical data available on these systems in the literature. (topical review)

High-resolution threshold photoelectron-photoion coincidence experiments performed on beamline 9.0.2.2: Kinetic energy release study of the process SF{sub 6} + hv {yields} SF{sub 5}{sup +} F + e{sup -}

Energy Technology Data Exchange (ETDEWEB)

Evans, M.; Ng, C.Y. [Ames Lab., IA (United States); Hsu, C.W.; Heimann, P. [Lawrence Berkeley National Lab., CA (United States)

1997-04-01

Vacuum ultraviolet (VUV) photoionization mass spectrometry has been used extensively to determine the energetics of neutral radicals and radical cations, as well as to study the dynamics of the dissociative photoionization process. Very often these measurements are concerned with determining the appearance energy (AE) for a dissociative ionization process, as well as determining the heats of formation of the species involved. One such photoionization mass spectrometric technique employed on End Station 2 of the Chemical Dynamics Beamline (9.0.2.2) at the Advanced Light Source is the threshold photoelectron-photoion coincidence (TPEPICO) method. TPEPICO involves measuring the time-of-flight (TOF) mass spectrum of a given cation in coincidence with threshold photoelectrons at a known photoionization energy.

New photoionization models of intergalactic clouds

Science.gov (United States)

Donahue, Megan; Shull, J. M.

1991-01-01

New photoionization models of optically thin low-density intergalactic gas at constant pressure, photoionized by QSOs, are presented. All ion stages of H, He, C, N, O, Si, and Fe, plus H2 are modeled, and the column density ratios of clouds at specified values of the ionization parameter of n sub gamma/n sub H and cloud metallicity are predicted. If Ly-alpha clouds are much cooler than the previously assumed value, 30,000 K, the ionization parameter must be very low, even with the cooling contribution of a trace component of molecules. If the clouds cool below 6000 K, their final equilibrium must be below 3000 K, owing to the lack of a stable phase between 6000 and 3000 K. If it is assumed that the clouds are being irradiated by an EUV power-law continuum typical of WSOs, with J0 = 10 exp -21 ergs/s sq cm Hz, typical cloud thicknesses along the line of sight that are much smaller than would be expected from shocks, thermal instabilities, or gravitational collapse are derived.

Ionization photophysics and Rydberg spectroscopy of diacetylene

KAUST Repository

Schwell, Martin

2012-11-01

Photoionization of diacetylene was studied using synchrotron radiation over the range 8-24 eV, with photoelectron-photoion coincidence (PEPICO) and threshold photoelectron-photoion coincidence (TPEPICO) techniques. Mass spectra, ion yields, total and partial ionization cross-sections were measured. The adiabatic ionization energy of diacetylene was determined as IE ad=(10.17±0.01) eV, and the appearance energy of the principal fragment ion C4H+ as AE=(16.15±0.03) eV. Calculated appearance energies of other fragment ions were used to infer aspects of dissociation pathways forming the weaker fragment ions C+ 4, C3H+, C+3 and C 4H+. Structured autoionization features observed in the PEPICO spectrum of diacetylene in the 11-13 eV region were assigned to vibrational components of three new Rydberg series, R1(nsσg, n=4-11), R2(ndσg, n=4-7) and R3(ndδg, n=4-6) converging to the A2Πu state of the cation, and to a new series R01(nsσg, n=3) converging to the B\\' 2Σ+u state of the cation. The autoionization mechanisms and their consistence with specific selection rules are discussed. © 2012 Taylor and Francis.

Ionization photophysics and Rydberg spectroscopy of diacetylene

KAUST Repository

Schwell, Martin; Bé nilan, Yves; Fray, Nicolas; Gazeau, Marie Claire; Es-sebbar, Et-touhami; Gaie-Levrel, Franç ois; Champion, Norbert; Leach, Sydney Sydney

2012-01-01

Photoionization of diacetylene was studied using synchrotron radiation over the range 8-24 eV, with photoelectron-photoion coincidence (PEPICO) and threshold photoelectron-photoion coincidence (TPEPICO) techniques. Mass spectra, ion yields, total and partial ionization cross-sections were measured. The adiabatic ionization energy of diacetylene was determined as IE ad=(10.17±0.01) eV, and the appearance energy of the principal fragment ion C4H+ as AE=(16.15±0.03) eV. Calculated appearance energies of other fragment ions were used to infer aspects of dissociation pathways forming the weaker fragment ions C+ 4, C3H+, C+3 and C 4H+. Structured autoionization features observed in the PEPICO spectrum of diacetylene in the 11-13 eV region were assigned to vibrational components of three new Rydberg series, R1(nsσg, n=4-11), R2(ndσg, n=4-7) and R3(ndδg, n=4-6) converging to the A2Πu state of the cation, and to a new series R01(nsσg, n=3) converging to the B' 2Σ+u state of the cation. The autoionization mechanisms and their consistence with specific selection rules are discussed. © 2012 Taylor and Francis.

A vacuum ultraviolet photoionization mass spectrometric study of acetone.

Science.gov (United States)

Wei, Lixia; Yang, Bin; Yang, Rui; Huang, Chaoqun; Wang, Jing; Shan, Xiaobin; Sheng, Liusi; Zhang, Yunwu; Qi, Fei; Lam, Chow-Shing; Li, Wai-Kee

2005-05-19

The photoionization and dissociative photoionization of acetone have been studied at the photon energy range of 8-20 eV. Photoionization efficiency spectra for ions CH3COCH3+, CH3+, C2H3+, C3H3+, C3H5+, CH(2-)CO+, CH3CO+, C3H4O+, and CH3COCH2+ have been measured. In addition, the energetics of the dissociative photoionization has been examined by ab initio Gaussian-3 (G3) calculations. The computational results are useful in establishing the dissociation channels near the ionization thresholds. With the help of G3 results, the dissociation channels for the formation of the fragment ions CH3CO+, CH2CO+, CH3+, C3H3+, and CH3COCH2+ have been established. The G3 results are in fair to excellent agreement with the experimental data.

Confinement and electron correlation effects in photoionization of atoms in endohedral anions: Ne-Cz-60

International Nuclear Information System (INIS)

Dolmatov, V K; Craven, G T; Keating, D

2010-01-01

Trends in resonances, termed confinement resonances, in photoionization of atoms A in endohedral fullerene anions A-C z- 60 are theoretically studied and exemplified by the photoionization of Ne in Ne-C z- 60 . Remarkably, above a particular nl ionization threshold of Ne in neutral Ne-C 60 (I z=0 nl ), confinement resonances in corresponding partial photoionization cross sections σ nl of Ne in any charged Ne-C z- 60 are not affected by a variation in the charge z of the carbon cage, as a general phenomenon. At lower photon energies, ω z=0 nl , the corresponding photoionization cross sections of charged Ne-C z- 60 (i.e., those with z ≠ 0) develop additional, strong, z-dependent resonances, termed Coulomb confinement resonances, as a general occurrence. Furthermore, near the innermost 1s ionization threshold, the 2p photoionization cross section σ 2p of the outermost 2p subshell of thus confined Ne is found to inherit the confinement resonance structure of the 1s photoionization spectrum, via interchannel coupling. As a result, new confinement resonances emerge in the 2p photoionization cross section of the confined Ne atom at photoelectron energies which exceed the 2p threshold by about a thousand eV, i.e., far above where conventional wisdom said they would exist. Thus, the general possibility for confinement resonances to resurrect in photoionization spectra of encapsulated atoms far above thresholds is revealed, as an interesting novel general phenomenon.

Absolute photoionization cross-section of the methyl radical.

Science.gov (United States)

Taatjes, Craig A; Osborn, David L; Selby, Talitha M; Meloni, Giovanni; Fan, Haiyan; Pratt, Stephen T

2008-10-02

The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; sigma(CH3)(10.2 eV) = (5.7 +/- 0.9) x 10(-18) cm(2) and sigma(CH3)(11.0 eV) = (6.0 +/- 2.0) x 10(-18) cm(2). The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH3 and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 +/- 2.0) x 10(-18) cm(2) at 10.460 eV, (5.5 +/- 2.0) x 10(-18) cm(2) at 10.466 eV, and (4.9 +/- 2.0) x 10(-18) cm(2) at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry.

Ignition method of corona discharge with modulation of the field in ion source of ion mobility spectrometer

International Nuclear Information System (INIS)

Gromov, Evgeniy

2011-01-01

The new method for the ignition of the corona discharge has been developed, which improves the stability of the ion mobility spectrometer and the resolution of the instrument. The system of forming a corona discharge without additional electrodes, which are used in a number of known structures for the pre-ionization, has been developed. This simplifies the design of the proposed source and an electronic control circuit. IMS technology is widely used in different civil and military fields for vapor-phase detection of explosive, narcotics, chemical warfare agents, biology molecules and so on. There are set of methods whose are used for the ionization of molecules under analysis. They are the following: radioactive ionization, ultraviolet photoionization, laser ionization, electric field ionization, corona spray ionization, electro spray ionization, roentgen ionization, and surface ionization. All these methods has their own advantages and disadvantages. A comparing of ion mobility spectra of non-polar hydrocarbons for photoionization, corona discharge ionization and 63 Ni ionization, had carried in. In our work we have investigated four types of IMS spectrometers whose use different sources for molecules under analysis ionization. They use radioactive ionization, ultraviolet photoionization, laser ionization, and roentgen ionization. The traditional explosives had investigated in experiments. In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor, which occurs when the potential gradient (the strength of the electric field) exceeds a certain value, but conditions are insufficient to cause complete electrical breakdown or arcing.

Photoionization studies of atoms and molecules using synchrotron radiation

International Nuclear Information System (INIS)

Lindle, D.W.

1988-01-01

Photoionization studies of free atoms and molecules have undergone considerable development in the past decade, in large part due to the use of synchrotron radiation. The tunability of synchrotron radiation has permitted the study of photoionization processes near valence-and core-level ionization thresholds for atoms and molecules throught the Periodic Table. A general illustration of these types of study will be presented, with emphasis on a few of the more promising new directions in atomic and molecular physics being pursued with synchrotron radiation. (author) [pt

Photodissociation and photoionization of organosulfur radicals

International Nuclear Information System (INIS)

Hsu, Chia-Wei.

1994-01-01

The dynamics of S( 3 P 2,1,0 , 1 D 2 ) production from the 193 nm photodissociation of CH 3 SCH 3 , H 2 S and CH 3 SH have been studied using 2 + 1 resonance-enhanced multiphoton ionization (REMPI) techniques. The 193 nm photodissociation cross sections for the formation of S from CH 3 S and HS initially prepared in the photodissociation of CH 3 SCH 3 and H 2 S are estimated to be 1 x 10 -18 and 1.1 x 10 -18 cm 2 , respectively. The dominant product from CH 3 S is S( 1 D), while that from SH is S( 3 P). Possible potential energy surfaces involved in the 193 nm photodissociation of CH 3 S(X) and SH(X) have been also examined. Threshold photoelectron (PE) spectra for SH and CH 3 S formed in the ultraviolet photodissociation of H 2 S and CH 3 SH, respectively, have been measured using the nonresonant two-photon pulsed field ionization (N2P-PFI) technique. The rotationally resolved N2P-PFI-PE spectrum obtained for SH indicates that photoionization dynamics favors the rotational angular momentum change ΔN 2 product 3,2 ) and CH 3 S(X 2 E 3/2 ) are determined to be 84,057.5 ± 3 cm -1 and 74,726 ± 8 cm -1 respectively. The spin-orbit splittings for SH(X 2 product 3/2,1/2 ) and CH 3 S(X 2 E 3/2,1/2 ) are found to be 377 ± 2 and 257 ± 5 cm -1 , respectively, in agreement with previous measurements. The C-S stretching frequency for CH 3 S + (X 3 A 2 ) is 733 ± 5 cm -1 . This study illustrates that the PFI-PE detection method can be a sensitive probe for the nascent internal energy distribution of photoproducts

Influence of the partial temporal coherence of short FEL pulses on two-colour photoionization and photoinduced Auger decay of atoms

International Nuclear Information System (INIS)

Kazansky, A K; Sazhina, I P; Kabachnik, N M

2013-01-01

The influence of the partial temporal coherence of free electron laser (FEL) radiation on the sidebands arising in the electron spectra of laser-assisted photoionization and photoinduced Auger decay of atoms is theoretically analysed. A simple model is developed which describes the inner-shell photoionization by a short (femtosecond) FEL pulse and the following Auger decay in a strong field of an infrared laser. The model is based on the time-dependent approach and uses the strong field approximation for both photo- and Auger electrons. Particular calculations have been carried out for Ne 1s photoionization and KLL Auger emission. We demonstrate that the temporal coherence of FEL pulses influences the line widths in the photoelectron spectrum. For a small coherence time the sidebands in this spectrum cannot be resolved. On the other hand, our calculations show that in the Auger electron spectrum the sidebands are practically independent of the coherence time of the ionizing pulse.

Photoionization in Ultraviolet Processing of Astrophysical Ice Analogs at Cryogenic Temperatures

Science.gov (United States)

Woon, David E.

2004-01-01

Two recent experimental studies have demonstrated that amino acids or amino acid precursors are generated when astrophysical ice analogs are subjected to ultraviolet (UV) irradiation at cryogenic temperatures. Understanding the complete phenomenology of photoprocessing is critical to elucidating chemical reaction mechanisms that can function within an ice matrix under very cold conditions. Pushing beyond the much better characterized study of photolytic dissociation of chemical bonds through electronic excitation, this work explored the ability of UV radiation present in the interstellar medium to ionize small molecules embedded in ices. Quantum chemical calculations, including bulk solvation effects, were used to study the ionization of hydrogen (H2), water, and methanol (CH3OH) bound in small clusters of water. Ionization potentials were found to be much smaller in the condensed phase than in the gas phase; even a small cluster can account for large changes in the ionization potentials in ice, as well as the known formation of an OH--H3O+ pair in the case of H2O photoionization. To gauge the impact of photoionization on subsequent grain chemistry, the reaction between OH and CO in the presence of H3O+ was studied and compared with the potential energy surface without hydronium present, which is relevant to chemistry following photolysis. The differences indicate that the reaction is somewhat more likely to proceed to products (H + CO2) in the case of photoionization.

Absolute photoionization cross-section measurements of the Kr I isoelectronic sequence

International Nuclear Information System (INIS)

Kilbane, D.; Banahan, C.; Kampen, P. van; Costello, J. T.; Folkmann, F.; Kjeldsen, H.; Bizau, J.-M.; Scully, S.; Mansfield, M. W. D.; West, J. B.

2007-01-01

Photoionization spectra have been recorded in the 4s, 4p, and 3d resonance regions for the Kr I isoelectronic sequence using both the dual laser produced plasma (DLP) technique (at DCU) to produce photoabsorption spectra, and the merged ion beam and synchrotron radiation technique (at ASTRID) to measure absolute photoionization cross sections. Profile parameters are compared for the 4s-np resonances of Rb + and Sr 2+ . Many 4p→ns, md transitions are identified with the aid of Hartree-Fock calculations, and consistent quantum defects are observed for the various ns and md Rydberg series. Absolute single and double photoionization cross sections recorded in the 3d region for Rb + and Sr 2+ ions show preferential decay via double photoionization. This is only the second report to our knowledge where both the DLP technique and the merged-beam technique have been used simultaneously to record photoionization spectra, and the advantages of both techniques (i.e., better resolution in the case of DLP and values for absolute photoionization cross sections in the case of the merged-beam technique) are highlighted

Experiments on how photo- and background ionization affect positive streamers: oxygen concentration, repetition and radioactivity

NARCIS (Netherlands)

Nijdam, S.; Veldhuizen, van E.M.; Ebert, U.

2011-01-01

Positive streamers in air and other oxygen-nitrogen mixtures are generally believed to propagate against the electron drift direction due to photo-ionization. Photo-ionization is the non-local ionization of O2-molecules by UV radiation from excited N2-molecules. This facilitates the streamer

Structural level characterization of base oils using advanced analytical techniques

KAUST Repository

Hourani, Nadim; Muller, Hendrik; Adam, Frederick M.; Panda, Saroj K.; Witt, Matthias; Al-Hajji, Adnan A.; Sarathy, Mani

2015-01-01

cyclotron resonance mass spectrometry (FT-ICR MS) equipped with atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) sources. First, the capabilities and limitations of each analytical technique were evaluated

Progress in zirconium resonance ionization spectroscopy

International Nuclear Information System (INIS)

Page, R.H.; Dropinski, S.C.; Worden, E.F.; Stockdale, J.A.D.

1993-01-01

The authors have examined the stepwise-resonant three-photon-ionization spectrum of neutral zirconium atoms using three separately-tunable pulsed visible dye lasers. The ground-level (first-step) transitions were chosen on the basis of demonstrated 91 Zr selectivity. Lifetimes of even-parity levels around 36,000 cm -1 , measured with the delayed-photoionization technique, range from 10 to 100 nsec. Direct ionization cross sections appear to be less than 10 -17 cm 2 ; newly-detected autoionizing levels give peak ionization cross sections (inferred from saturation fluences) up to 10 -15 cm 2 . Portions of Rydberg series converging to the 315 and 763 cm -1 levels of Zr + were identified. Clumps of autoionizing levels are thought to be due to Rydberg-valence mixing

Ionization photophysics and spectroscopy of dicyanoacetylene

International Nuclear Information System (INIS)

Leach, Sydney; Champion, Norbert; Schwell, Martin; Bénilan, Yves; Fray, Nicolas; Gazeau, Marie-Claire; Garcia, Gustavo A.; Gaie-Levrel, François; Guillemin, Jean-Claude

2013-01-01

Photoionization of dicyanoacetylene was studied using synchrotron radiation over the excitation range 8–25 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and detailed spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of dicyanoacetylene was measured as 11.80 ± 0.01 eV. A detailed analysis of the cation spectroscopy involves new aspects and new assignments of the vibrational components to excitation of the quasi-degenerate A 2 Π g , B 2 Σ g + states as well as the C 2 Σ u + and D 2 Π u states of the cation. Some of the structured autoionization features observed in the 12.4–15 eV region of the total ion yield spectrum were assigned to vibrational components of valence shell transitions and to two previously unknown Rydberg series converging to the D 2 Π u state of C 4 N 2 + . The appearance energies of the fragment ions C 4 N + , C 3 N + , C 4 + , C 2 N + , and C 2 + were measured and their heats of formation were determined and compared with existing literature values. Thermochemical calculations of the appearance potentials of these and other weaker ions were used to infer aspects of dissociative ionization pathways

Study of higher hydrocarbon production during ethylacetylene pyrolysis using laser-generated vacuum-ultraviolet photoionization detection

Energy Technology Data Exchange (ETDEWEB)

Boyle, J.; Pfefferle, L. (Yale Univ., New Haven, CT (USA))

1990-04-19

Higher hydrocarbon formation during the pyrolysis of ethylacetylene in a microjet reactor was studied by vacuum-ultraviolet photoionization time-of-flight mass spectrometry. At the wavelength employed, this ionization technique allows for the simultaneous detection of both stable and intermediate polyatomic species with ionization potentials below 10.49 eV, including most hydrocarbons with two or more carbon atoms. Minimal fragmentation simplifies the determination of parent species and allows identification of probable reaction pathways involving hydrocarbon radicals as well as stable species. The pyrolysis of ethylacetylene was carried out in the fast-flow microjet reactor (residence times 1-2 ms) at temperatures from 300 to 1,600 K.

Photoionization of image states around metallic nanotubes

Energy Technology Data Exchange (ETDEWEB)

Segui, Silvina; Arista, Nestor R; Gervasoni, Juana L [Centro Atomico Bariloche (CNEA) 8400, Rio Negro (Argentina); Bocan, Gisela A, E-mail: segui@cab.cnea.gov.a, E-mail: gbocan@iafe.uba.a, E-mail: arista@cab.cnea.gov.a, E-mail: gervason@cab.cnea.gov.a [Institute de AstronomIa y Fisica del Espacio, CC 67, Sue 28, 1428, Ciudad Universitaria, Buenos Aires (Argentina)

2009-11-01

In this work we study a theoretical approach to the ionization of electrons bound in an image state around a metallic nanotube by the impact of photons. In a close analogy to the already studied case of ionization by electron impact [1], we calculate and analyze photoionization cross sections of tubular image states [2] within a first Born approximation. We consider various situations, including different energies and polarizations of the incident photon, ejection directions of the outgoing electron, and angular momenta of the image state.

Rotationally resolved state-to-state photoionization and the photoelectron study of vanadium monocarbide and its cations (VC/VC(+)).

Science.gov (United States)

Chang, Yih Chung; Luo, Zhihong; Pan, Yi; Zhang, Zheng; Song, Ying-Nan; Kuang, Sophie Yajin; Yin, Qing Zhu; Lau, Kai-Chung; Ng, C Y

2015-04-21

By employing two-color visible (VIS)-ultraviolet (UV) laser photoionization and pulsed field ionization-photoelectron (PFI-PE) techniques, we have obtained highly rotationally resolved photoelectron spectra for vanadium monocarbide cations (VC(+)). The state-to-state VIS-UV-PFI-PE spectra thus obtained allow unambiguous assignments for the photoionization rotational transitions, resulting in a highly precise value for the adiabatic ionization energy (IE) of vanadium monocarbide (VC), IE(VC) = 57512.0 ± 0.8 cm(-1) (7.13058 ± 0.00010 eV), which is defined as the energy of the VC(+)(X(3)Δ1; v(+) = 0; J(+) = 1) ← VC(X(2)Δ3/2; v'' = 0; J'' = 3/2) photoionization transition. The spectroscopic constants for VC(+)(X(3)Δ1) determined in the present study include the harmonic vibrational frequency ωe(+) = 896.4 ± 0.8 cm(-1), the anharmonicity constant ωe(+)xe(+) = 5.7 ± 0.8 cm(-1), the rotational constants Be(+) = 0.6338 ± 0.0025 cm(-1) and αe(+) = 0.0033 ± 0.0007 cm(-1), the equilibrium bond length re(+) = 1.6549 ± 0.0003 Å, and the spin-orbit coupling constant A = 75.2 ± 0.8 cm(-1) for VC(+)(X(3)Δ1,2,3). These highly precise energetic and spectroscopic data are used to benchmark state-of-the-art CCSDTQ/CBS calculations. In general, good agreement is found between the theoretical predictions and experimental results. The theoretical calculations yield the values, IE(VC) = 7.126 eV; the 0 K bond dissociation energies: D0(V-C) = 4.023 eV and D0(V(+)-C) = 3.663 eV; and heats of formation: ΔH°(f0)(VC) = 835.2, ΔH°(f298)(VC) = 840.4, ΔH°(f0)(VC(+)) = 1522.8, and ΔH°(f298)(VC(+)) = 1528.0 kJ mol(-1).

Spatially resolved photoionization of ultracold atoms on an atom chip

International Nuclear Information System (INIS)

Kraft, S.; Guenther, A.; Fortagh, J.; Zimmermann, C.

2007-01-01

We report on photoionization of ultracold magnetically trapped Rb atoms on an atom chip. The atoms are trapped at 5 μK in a strongly anisotropic trap. Through a hole in the chip with a diameter of 150 μm, two laser beams are focused onto a fraction of the atomic cloud. A first laser beam with a wavelength of 778 nm excites the atoms via a two-photon transition to the 5D level. With a fiber laser at 1080 nm the excited atoms are photoionized. Ionization leads to depletion of the atomic density distribution observed by absorption imaging. The resonant ionization spectrum is reported. The setup used in this experiment is suitable not only to investigate mixtures of Bose-Einstein condensates and ions but also for single-atom detection on an atom chip

Measurement of the ratio of double-to-single photoionization of helium at 2.8 keV using synchrotron radiation

International Nuclear Information System (INIS)

Levin, J.C.; Lindle, D.W.; Keller, N.; Miller, R.D.; Azuma, Y.; Mansour, N.B.; Berry, H.G.; Sellin, I.A.

1991-01-01

We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find He ++ /He + =1.6±0.3% at hν=2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Aberg, who predict 1.7%

Penning ionization processes studied by electron spectroscopy

International Nuclear Information System (INIS)

Yencha, A.J.

1978-01-01

The technique of measuring the kinetic energy of electrons ejected from atomic or molecular species as a result of collisional energy transfer between a metastable excited rare gas atom and an atom or molecule is known as Penning ionization spectroscopy. Like the analogous photoionization process of photoelectron spectroscopy, a considerable amount of information has been gained about the ionization potentials of numerous molecular systems. It is, in fact, through the combined analyses of photoelectron and Penning electron spectra that affords a probe of the particle-particle interactions that occur in the Penning process. In this paper a short survey of the phenomenon of Penning ionization, as studied by electron spectroscopy, will be presented as it pertains to the ionization processes of simple molecules by metastable excited atoms. (author)

Ultrafast quantum control of ionization dynamics in krypton.

Science.gov (United States)

Hütten, Konrad; Mittermair, Michael; Stock, Sebastian O; Beerwerth, Randolf; Shirvanyan, Vahe; Riemensberger, Johann; Duensing, Andreas; Heider, Rupert; Wagner, Martin S; Guggenmos, Alexander; Fritzsche, Stephan; Kabachnik, Nikolay M; Kienberger, Reinhard; Bernhardt, Birgitta

2018-02-19

Ultrafast spectroscopy with attosecond resolution has enabled the real time observation of ultrafast electron dynamics in atoms, molecules and solids. These experiments employ attosecond pulses or pulse trains and explore dynamical processes in a pump-probe scheme that is selectively sensitive to electronic state of matter via photoelectron or XUV absorption spectroscopy or that includes changes of the ionic state detected via photo-ion mass spectrometry. Here, we demonstrate how the implementation of combined photo-ion and absorption spectroscopy with attosecond resolution enables tracking the complex multidimensional excitation and decay cascade of an Auger auto-ionization process of a few femtoseconds in highly excited krypton. In tandem with theory, our study reveals the role of intermediate electronic states in the formation of multiply charged ions. Amplitude tuning of a dressing laser field addresses different groups of decay channels and allows exerting temporal and quantitative control over the ionization dynamics in rare gas atoms.

Novel technique for coal pyrolysis and hydrogenation production analysis

Energy Technology Data Exchange (ETDEWEB)

Pfefferle, L.D.

1990-01-01

The overall objective of this study is to establish vacuum ultraviolet photoionization-MS and VUV pulsed EI-MS as useful tools for a simpler and more accurate direct mass spectrometric measurement of a broad range of hydrocarbon compounds in complex mixtures for ultimate application to the study of the kinetics of coal hydrogenation and pyrolysis processes. The VUV-MS technique allows ionization of a broad range of species with minimal fragmentation. Many compounds of interest can be detected with the 118 nm wavelength, but additional compound selectivity is achievable by tuning the wavelength of the photo-ionization source in the VUV. Resonant four wave mixing techniques in Hg vapor will allow near continuous tuning from about 126 to 106 nm. This technique would facilitate the scientific investigation of coal upgrading processes such as pyrolysis and hydrogenation by allowing accurate direct analysis of both stable and intermediate reaction products.

Electron-electron correlation in two-photon double ionization of He-like ions

Science.gov (United States)

Hu, S. X.

2018-01-01

Electron correlation plays a crucial role in quantum many-body physics ranging from molecular bonding and strong-field-induced multielectron ionization, to superconducting in materials. Understanding the dynamic electron correlation in the photoionization of relatively simple quantum three-body systems, such as He and He-like ions, is an important step toward manipulating complex systems through photoinduced processes. Here we have performed ab initio investigations of two-photon double ionization (TPDI) of He and He-like ions (L i+,B e2 + , and C4 +) exposed to intense attosecond x-ray pulses. Results from such fully correlated quantum calculations show weaker and weaker electron correlation effects in TPDI spectra as the ionic charge increases, which is opposite to the intuition that the absolute increase of correlation in the ground state should lead to more equal energy sharing in photoionization. These findings indicate that the final-state electron-electron correlation ultimately determines the energy sharing of the two ionized electrons in TPDI.

Photoionization of excited atoms and ions: recent progress and future prospects

International Nuclear Information System (INIS)

Wuilleumier, F.J.

2004-01-01

Full text: Photoionization of atoms in the ground state using synchrotron radiation (SR) has contributed extensively to a better knowledge of atomic structure and of its dynamical response to photon interaction. Since the st use in 1963 of an SR facility in the ultraviolet to investigate autoionizing states in helium, each improvement in the performance of available SR beams has allowed to go deeper and deeper into the understanding of isolated atomic systems. The study of very dilute targets such as atoms prepared in selected excited states or multiply-charged ions is more challenging. Using dye lasers, the excited state can be prepared with a well defined set of quantum numbers and SR photoionization of this prepared state can be studied as a function of photon energy and emission-angle. For ions, the equivalent ionic densities achievable in a merged-beam experiment do not exceed, usually, 10 6 cm -3 , i.e. they are lower by 5 orders of magnitude than for atoms in the ground state. This explains why the response of ionized matter to photoionizing radiation has been largely unexplored until recently. Theoretical methods, still to be tested by experimental measurements, have been developed to model stellar atmospheres as well as laboratory plasmas. After the pioneering experiments using plasma discharge technology and laser-produced plasmas to measure photoionization in excited states and ions, the use of SR has allowed to dramatically improve experiments for excited- and ionic-species, starting with the first measurements of electron spectra from photoionization of laser-excited sodium atoms, and with the first determination of doubly-charged ion rate resulting from photoionization of singly-charged ions in merged beam experiments. Over the past 5 years, photoionization of singly- and multiply-charged ions using the merged beam technique has been intensively performed at four SR facilities (ASTRID, Spring-8, the Advanced Light Source (ALS), and Super-ACO), all of

Partial Photoionization Cross Sections and Angular Distributions for Double Excitation of Helium up to the N=13 Threshold

International Nuclear Information System (INIS)

Czasch, A.; Schoeffler, M.; Hattass, M.; Schoessler, S.; Jahnke, T.; Weber, Th.; Staudte, A.; Titze, J.; Wimmer, C.; Kammer, S.; Weckenbrock, M.; Voss, S.; Grisenti, R.E.; Jagutzki, O.; Schmidt, L.Ph.H.; Schmidt-Boecking, H.; Doerner, R.; Rost, J.M.; Schneider, T.; Liu, C.-N.

2005-01-01

Partial photoionization cross sections σ N (E γ ) and photoelectron angular distributions β N (E γ ) were measured for the final ionic states He + (N>4) in the region between the N=8 and N=13 thresholds (E γ >78.155 eV) using the cold target recoil ion momentum spectroscopy technique (COLTRIMS). Comparison of the experimental data with two independent sets of theoretical predictions reveals disagreement for the branching ratios to the various He N + states. The angular distributions just below the double ionization threshold suggest an excitation process for highly excited N states similar to the Wannier mechanism for double ionization

Vacuum ultraviolet photofragmentation of octadecane: photoionization mass spectrometric and theoretical investigation.

Science.gov (United States)

Xu, Jing; Sang, Pengpeng; Zhao, Lianming; Guo, Wenyue; Qi, Fei; Xing, Wei; Yan, Zifeng

The photoionization and fragmentation of octadecane were investigated with infrared laser desorption/tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (IRLD/VUV PIMS) and theoretical calculations. Mass spectra of octadecane were measured at various photon energies. The fragment ions were gradually detected with the increase of photon energy. The main fragment ions were assigned to radical ions (C n H 2 n +1 + , n  = 4-11) and alkene ions (C n H 2 n + , n  = 5-10). The ionization energy of the precursor and appearance energy of ionic fragments were obtained by measuring the photoionization efficiency spectrum. Possible formation pathways of the fragment ions were discussed with the help of density functional theory calculations.

Hyphenation of two simultaneously employed soft photo ionization mass spectrometers with thermal analysis of biomass and biochar

International Nuclear Information System (INIS)

Fendt, Alois; Geissler, Robert; Streibel, Thorsten

2013-01-01

Highlights: ► First simultaneous hyphenation of two time-of-flight mass spectrometers with different soft photo ionization techniques (SPI and REMPI) to Thermal Analysis using a newly developed prototype for EGA is presented. ► Resonance enhanced multi-photon ionization (REMPI) enables sensitive and selective analysis of aromatic species. ► Single photon ionization (SPI) using VUV light supplied by an innovative electron-beam pumped excimer light source (EBEL) comprehensively ionizes (nearly) all organic molecules. ► The resulting mass spectra show distinct patterns for the evolved gases of the miscellaneous biomasses and chars thereof. ► The potential for detailed kinetic studies is apparent on account of the complex pyrolysis gas compositions. - Abstract: Evolved gas analysis (EGA) is a powerful and complementary tool for Thermal Analysis. In this context, two time-of-flight mass spectrometers with different soft photo-ionization techniques are simultaneously hyphenated to a thermo balance and applied in form of a newly developed prototype for EGA of pyrolysis gases from biomass and biochar. Resonance enhanced multi-photon ionization (REMPI) is applied for selective analysis of aromatic species. Furthermore, single photon ionization (SPI) using VUV light supplied by an electron-beam pumped excimer light source (EBEL) was used to comprehensively ionize (nearly) all organic molecules. The soft ionization capability of photo-ionization techniques allows direct and on-line analysis of the evolved pyrolysis gases. Characteristic mass spectra with specific patterns could be obtained for the miscellaneous biomass feeds used. Temperature profiles of the biochars reveal a desorption step, followed by pyrolysis as observed for the biomasses. Furthermore, the potential for kinetic studies is apparent for this instrumental setup.

Combination of electrospray ionization, atmospheric pressure photoionization and laser desorption ionization Fourier transform ion cyclotronic resonance mass spectrometry for the investigation of complex mixtures - Application to the petroleomic analysis of bio-oils.

Science.gov (United States)

Hertzog, Jasmine; Carré, Vincent; Le Brech, Yann; Mackay, Colin Logan; Dufour, Anthony; Mašek, Ondřej; Aubriet, Frédéric

2017-05-29

The comprehensive description of complex mixtures such as bio-oils is required to understand and improve the different processes involved during biological, environmental or industrial operation. In this context, we have to consider how different ionization sources can improve a non-targeted approach. Thus, the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been coupled to electrospray ionization (ESI), laser desorption ionization (LDI) and atmospheric pressure photoionization (APPI) to characterize an oak pyrolysis bio-oil. Close to 90% of the all 4500 compound formulae has been attributed to C x H y O z with similar oxygen class compound distribution. Nevertheless, their relative abundance in respect with their double bound equivalent (DBE) value has evidenced significant differences depending on the ion source used. ESI has allowed compounds with low DBE but more oxygen atoms to be ionized. APPI has demonstrated the efficient ionization of less polar compounds (high DBE values and less oxygen atoms). The LDI behavior of bio-oils has been considered intermediate in terms of DBE and oxygen amounts but it has also been demonstrated that a significant part of the features are specifically detected by this ionization method. Thus, the complementarity of three different ionization sources has been successfully demonstrated for the exhaustive characterization by petroleomic approach of a complex mixture. Copyright © 2017 Elsevier B.V. All rights reserved.

Absolute high-resolution Se+ photoionization cross-section measurements with Rydberg-series analysis

International Nuclear Information System (INIS)

Esteves, D. A.; Bilodeau, R. C.; Sterling, N. C.; Phaneuf, R. A.; Kilcoyne, A. L. D.; Red, E. C.; Aguilar, A.

2011-01-01

Absolute single photoionization cross-section measurements for Se + ions were performed at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory using the photo-ion merged-beams technique. Measurements were made at a photon energy resolution of 5.5 meV from 17.75 to 21.85 eV spanning the 4s 2 4p 3 4 S 3/2 o ground-state ionization threshold and the 2 P 3/2 o , 2 P 1/2 o , 2 D 5/2 o , and 2 D 3/2 o metastable state thresholds. Extensive analysis of the complex resonant structure in this region identified numerous Rydberg series of resonances and obtained the Se 2+ 4s 2 4p 23 P 2 and 4s 2 4p 21 S 0 state energies. In addition, particular attention was given to removing significant effects in the measurements due to a small percentage of higher-order undulator radiation.

Higher-order processes in x-ray photoionization of atoms

International Nuclear Information System (INIS)

Kanter, E. P.; Dunford, R. W.; Krassig, B.; Southworth, S. H.; Young, L.

2006-01-01

There are several fourth-generation X-ray light source projects now underway around the world and it is anticipated that by the end of the decade, one or more of these X-ray free-electron lasers will be operational. In this contribution, we describe recent measurements and future plans to study both multielectron and multiphoton atomic photoionization. Although such higher-order processes are rare with present third-generation sources, they will be commonplace in experimental work with the new sources. The topics we discuss here are double K-shell ionization and two-photon X-ray photoionization

Application of time-of-flight mass spectrometry with laser-based photoionization methods for analytical pyrolysis of PVC

Energy Technology Data Exchange (ETDEWEB)

Streibel, T.; Muehlberger, F. [GSF - Forschungszentrum fuer Umwelt und Gesundheit GmbH, Neuherberg (Germany); Adam, T.; Zimmermann, R. [Augsburg Univ. (Germany); Cao, L. [National Center for Iron and Steel, Beijing, BJ (China)

2004-09-15

Chlorinated benzenes and phenols generated from PVC pyrolysis are known to be precursors of PCDD/F formation. Therefore, selective and sensitive monitoring of these substances during PVC pyrolysis processes on an on-line, real-time basis could be very useful for the understanding of PCDD/F formation pathways. In this study, we investigated the pyrolysis gas from PVC samples derived from steel recycling by means of simultaneous single photon ionization/resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (SPI/REMPI-TOFMS). The application of these soft photo-ionization techniques in mass spectrometry enables a fast and comprehensive analysis of this complex matrix without generating fragment ions, which would interfere with molecule ions making interpretation of the obtained mass spectra very difficult.

Effects of time-dependent photoionization on interstellar pickup atoms

International Nuclear Information System (INIS)

Isenberg, P.A.; Lee, M.A.

1995-01-01

We present an analytical model for the density variations of interstellar pickup ions in the solar wind due to a time-dependent variation in the photoionization rate, our model predicts a pickup ion density enhancement lasting for a time of the order of the duration of the increase plus the solar wind convection time to the observation point. If the photoionization rate returns to its initial value, this enhancement is followed by a decreased pickup ion density resulting from a depleted interstellar neutral particle density. In the absence of further variations in the photoionization rate, the pickup ion density recovers on a time which scales as the radial position of the observation point divided by the inflow speed of the neutral particles. Gradual variations in the photoionization rate result in a pickup ion density which tends to track the ionization rate, though the density variations are smoothed and delayed in time due to the solar wind convection of ions picked up at points closer to the Sun. 27 refs., 4 figs

Photoionization mass spectrometer for studies of flame chemistry with a synchrotron light source

International Nuclear Information System (INIS)

Cool, Terrill A.; McIlroy, Andrew; Qi, Fei; Westmoreland, Phillip R.; Poisson, Lionel; Peterka, Darcy S.; Ahmed, Musahid

2005-01-01

A flame-sampling molecular-beam photoionization mass spectrometer, recently designed and constructed for use with a synchrotron-radiation light source, provides significant improvements over previous molecular-beam mass spectrometers that have employed either electron-impact ionization or vacuum ultraviolet laser photoionization. These include superior signal-to-noise ratio, soft ionization, and photon energies easily and precisely tunable [E/ΔE(FWHM)≅250-400] over the 7.8-17-eV range required for quantitative measurements of the concentrations and isomeric compositions of flame species. Mass resolution of the time-of-flight mass spectrometer is m/Δm=400 and sensitivity reaches ppm levels. The design of the instrument and its advantages for studies of flame chemistry are discussed

The effect of the electric field on the photoionization cross-section

International Nuclear Information System (INIS)

Sali, A.; Loumrhari, H.; Fliyou, M.

1998-01-01

The effect of the electric field on the donor impurity is investigated in the case of a spherical conduction band with the use of a variational procedure. An analytical expression for the photoionization cross-section as a function of photon energy within the effective mass approximation of an impurity atom in an applied field was obtained. The effect of central cell correction by means of a semi-empirical short-range potential is taken into account. It has been found that the binding energy and the spectral dependence of the cross-section are very sensitive to the electric field, the shape of the impurity potential and their combined effect

Effects of ultrashort laser pulses on angular distributions of photoionization spectra.

Science.gov (United States)

Ooi, C H Raymond; Ho, W L; Bandrauk, A D

2017-07-27

We study the photoelectron spectra by intense laser pulses with arbitrary time dependence and phase within the Keldysh framework. An efficient semianalytical approach using analytical transition matrix elements for hydrogenic atoms in any initial state enables efficient and accurate computation of the photoionization probability at any observation point without saddle point approximation, providing comprehensive three dimensional photoelectron angular distribution for linear and elliptical polarizations, that reveal the intricate features and provide insights on the photoionization characteristics such as angular dispersions, shift and splitting of photoelectron peaks from the tunneling or above threshold ionization(ATI) regime to non-adiabatic(intermediate) and multiphoton ionization(MPI) regimes. This facilitates the study of the effects of various laser pulse parameters on the photoelectron spectra and their angular distributions. The photoelectron peaks occur at multiples of 2ħω for linear polarization while  odd-ordered peaks are suppressed in the direction perpendicular to the electric field. Short pulses create splitting and angular dispersion where the peaks are strongly correlated to the angles. For MPI and elliptical polarization with shorter pulses the peaks split into doublets and the first peak vanishes. The carrier envelope phase(CEP) significantly affects the ATI spectra while the Stark effect shifts the spectra of intermediate regime to higher energies due to interference.

Resonance ionization detection of combustion radicals

Energy Technology Data Exchange (ETDEWEB)

Cool, T.A. [Cornell Univ., Ithaca, NY (United States)

1993-12-01

Fundamental research on the combustion of halogenated organic compounds with emphasis on reaction pathways leading to the formation of chlorinated aromatic compounds and the development of continuous emission monitoring methods will assist in DOE efforts in the management and disposal of hazardous chemical wastes. Selective laser ionization techniques are used in this laboratory for the measurement of concentration profiles of radical intermediates in the combustion of chlorinated hydrocarbon flames. A new ultrasensitive detection technique, made possible with the advent of tunable VUV laser sources, enables the selective near-threshold photoionization of all radical intermediates in premixed hydrocarbon and chlorinated hydrocarbon flames.

Effect of magnetic field on selectivity of three-step photoionization

International Nuclear Information System (INIS)

Lim, Chang Hwan; Rho, Si Pyo; Ko, Kwang Hoon; Kim, Chul Joong; Izawa, Yasukazu

2001-01-01

Effect of magnetic field on selectivity by linearly polarized lasers was analyzed by formulating the density matrix equations. To investigate the effect of magnetic field on the selectivity of AVLIS, we proposed a general Hamiltonian for multilevel atomic system in magnetic field. The population dynamics of magnetic sublevels have been observed by solving the Liouville equation. Mixing between magnetic sublevels was observed in each state during the laser excitations when the magnetic field perpendicular to the quantization axis was applied to the atomic system. The magnetic field dependence on ionization rate of even isotopes was also discussed. In the magnetic field dependence, two ionization peaks were appeared because of the interference between Rabi and Larmor frequency during the ionization process. The permissible intensities of magnetic field were predicted to obtain enough selectivity for the target isotopes of zirconium and gadolinium in the AVLIS process based on the polarization selection rule

VUV photoionization of acetamide studied by electron/ion coincidence spectroscopy in the 8–24 eV photon energy range

International Nuclear Information System (INIS)

Schwell, Martin; Bénilan, Yves; Fray, Nicolas; Gazeau, Marie-Claire; Es-Sebbar, Et.; Garcia, Gustavo A.; Nahon, Laurent; Champion, Norbert; Leach, Sydney

2012-01-01

Highlights: ► We study the VUV photoionization of acetamide in the 8–24 eV photon energy range. ► Electron/ion coincidence measurements are performed using synchrotron radiation. ► The adiabatic ionization energy of acetamide is determined by TPEPICO measurements. ► VUV induced fragmentation pathways of acetamide are assigned and discussed. - Abstract: A VUV photoionization study of acetamide was carried out over the 8–24 eV photon energy range using synchrotron radiation and photoelectron/photoion coincidence (PEPICO) spectroscopy. Threshold photoelectron photoion coincidence (TPEPICO) measurements were also made. Photoion yield curves and branching ratios were measured for the parent ion and six fragment ions. The adiabatic ionization energy of acetamide was determined as I.E. (1 2 A′) = (9.71 ± 0.02) eV, in agreement with an earlier reported photoionization mass spectrometry (PIMS) value. The adiabatic energy of the first excited state of the ion, 1 2 A″, was determined to be ≈10.1 eV. Assignments of the fragment ions and the pathways of their formation by dissociative photoionization were made. The neutral species lost in the principal dissociative photoionization processes are CH 3 , NH 2 , NH 3 , CO, HCCO and NH 2 CO. Heats of formation are derived for all ions detected and are compared with literature values. Some astrophysical implications of these results are discussed.

Photoionization mass spectrometry of UF6

International Nuclear Information System (INIS)

Berkowitz, J.

1979-01-01

The photoionization mass spectrum of 238 UF 6 was obtained. At 600 A = 20.66 eV, the relative ionic abundances were as follows: UF 6 + , 1.4; UF 5 + , 100; UF + , 17; UF 3 + , approx. 0.7; UF 2 + , very weak; UF + , very weak; U + , essentially zero. The adiabatic ionization potential for UF 6 was 13.897 +- 0.005 eV. The production of UF 5 + begins at approx. 887 A = 13.98 eV, at which energy the UF 6 + partial cross section abruptly declines and then levels off. This behavior suggests the vague possibility of an isotope effect. The UF 4 + signal begins at approx. 725 A = 17.10 eV, at which energy the UF 5 + signal reaches a plateau value. The UF 5 + photoionization yield curve displays some autoionization structure from its threshold to approx. 750 A

Effects of uniform dc electric fields on multiphoton ionization of cesium atoms

International Nuclear Information System (INIS)

Klots, C.E.; Compton, R.N.

1985-01-01

Multiphoton ionization of cesium atoms shows pronounced two-photon resonances at the nd states and, to a much smaller extent, at the ns states. A dc electric field augments the ns resonances and, for a complementary reason, induces resonances at the np and nf levels. A scaling law for field-induced signals, as a function of principal quantum number, is reported. Field ionization of high Rydberg states is also conveniently studied and quantified with our technique

Hyphenation of two simultaneously employed soft photo ionization mass spectrometers with thermal analysis of biomass and biochar

Energy Technology Data Exchange (ETDEWEB)

Fendt, Alois [Joint Mass Spectrometry Centre, Chair of Analytical Chemistry, Institute of Chemistry, University of Rostock, 18059 Rostock (Germany); Joint Mass Spectrometry Centre, Cooperation Group for Analysis of Complex Molecular Systems, Institute of Ecological Chemistry, Helmholtz Zentrum Muenchen - German Research Center for Environmental Health (GmbH), IngolstaedterLandstr. 1, 85764 Neuherberg (Germany); Analytical Chemistry, Institute of Physics, University of Augsburg, 86159 Augsburg (Germany); Geissler, Robert [Joint Mass Spectrometry Centre, Cooperation Group for Analysis of Complex Molecular Systems, Institute of Ecological Chemistry, Helmholtz Zentrum Muenchen - German Research Center for Environmental Health (GmbH), IngolstaedterLandstr. 1, 85764 Neuherberg (Germany); Analytical Chemistry, Institute of Physics, University of Augsburg, 86159 Augsburg (Germany); Streibel, Thorsten, E-mail: thorsten.streibel@uni-rostock.de [Joint Mass Spectrometry Centre, Chair of Analytical Chemistry, Institute of Chemistry, University of Rostock, 18059 Rostock (Germany); Joint Mass Spectrometry Centre, Cooperation Group for Analysis of Complex Molecular Systems, Institute of Ecological Chemistry, Helmholtz Zentrum Muenchen - German Research Center for Environmental Health (GmbH), IngolstaedterLandstr. 1, 85764 Neuherberg (Germany); and others

2013-01-10

Highlights: Black-Right-Pointing-Pointer First simultaneous hyphenation of two time-of-flight mass spectrometers with different soft photo ionization techniques (SPI and REMPI) to Thermal Analysis using a newly developed prototype for EGA is presented. Black-Right-Pointing-Pointer Resonance enhanced multi-photon ionization (REMPI) enables sensitive and selective analysis of aromatic species. Black-Right-Pointing-Pointer Single photon ionization (SPI) using VUV light supplied by an innovative electron-beam pumped excimer light source (EBEL) comprehensively ionizes (nearly) all organic molecules. Black-Right-Pointing-Pointer The resulting mass spectra show distinct patterns for the evolved gases of the miscellaneous biomasses and chars thereof. Black-Right-Pointing-Pointer The potential for detailed kinetic studies is apparent on account of the complex pyrolysis gas compositions. - Abstract: Evolved gas analysis (EGA) is a powerful and complementary tool for Thermal Analysis. In this context, two time-of-flight mass spectrometers with different soft photo-ionization techniques are simultaneously hyphenated to a thermo balance and applied in form of a newly developed prototype for EGA of pyrolysis gases from biomass and biochar. Resonance enhanced multi-photon ionization (REMPI) is applied for selective analysis of aromatic species. Furthermore, single photon ionization (SPI) using VUV light supplied by an electron-beam pumped excimer light source (EBEL) was used to comprehensively ionize (nearly) all organic molecules. The soft ionization capability of photo-ionization techniques allows direct and on-line analysis of the evolved pyrolysis gases. Characteristic mass spectra with specific patterns could be obtained for the miscellaneous biomass feeds used. Temperature profiles of the biochars reveal a desorption step, followed by pyrolysis as observed for the biomasses. Furthermore, the potential for kinetic studies is apparent for this instrumental setup.

Classical two-split interference effects in double photoionization of molecular hydrogen at high energies

Energy Technology Data Exchange (ETDEWEB)

Horner, Daniel A [Los Alamos National Laboratory; Miyabe, S [LBNL; Rescigno, T N [LBNL; Mccurdy, C W [LBNL; Morales, F [MADRID, SPAIN; Martin, F [MADRID, SPAIN

2009-01-01

The authors report a thorough theoretical study of one photon double ionization of H{sub 2}. They suggest that interference effects reported in one photon ionization will be reproducible in the case of double ionization when one of the photons carriers most of the available energy and the other electron is not observed. These calculations reproduce recent double photoionization experiments of H{sub 2}.

Toward Rotational State-Selective Photoionization of ThF+ Ions

Science.gov (United States)

Zhou, Yan; Ng, Kia Boon; Gresh, Dan; Cairncross, William; Grau, Matt; Ni, Yiqi; Cornell, Eric; Ye, Jun

2016-06-01

ThF+ has been chosen to replace HfF+ for a second-generation measurement of the electric dipole moment of the electron (eEDM). Compared to the currently running HfF+ eEDM experiment, ThF+ has several advantages: (i) the eEDM-sensitive state (3Δ1) is the ground state, which facilitates a long coherence time [1]; (ii) its effective electric field (35 GV/cm) is 50% larger than that of HfF+, which promises a direct increase of the eEDM sensitivity [2]; and (iii) the ionization energy of neutral ThF is lower than its dissociation energy, which introduces greater flexibility in rotational state-selective photoionization via core-nonpenetrating Rydberg states [3]. In this talk, we first present our strategy of preparing and utilizing core-nonpenetrating Rydberg states for rotational state-selective ionization. Then, we report spectroscopic data of laser-induced fluorescence of neutral ThF, which provides critical information for multi-photon ionization spectroscopy. [1] D. N. Gresh, K. C. Cossel, Y. Zhou, J. Ye, E. A. Cornell, Journal of Molecular Spectroscopy, 319 (2016), 1-9 [2] M. Denis, M. S. Nørby, H. J. A. Jensen, A. S. P. Gomes, M. K. Nayak, S. Knecht, T. Fleig, New Journal of Physics, 17 (2015) 043005. [3] Z. J. Jakubek, R. W. Field, Journal of Molecular Spectroscopy 205 (2001) 197-220.

Synchrotron Photoionization Investigation of the Oxidation of Ethyl tert-Butyl Ether.

Science.gov (United States)

Winfough, Matthew; Yao, Rong; Ng, Martin; Catani, Katherine; Meloni, Giovanni

2017-02-23

The oxidation of ethyl tert-butyl ether (ETBE), a widely used fuel oxygenated additive, is investigated using Cl atoms as initiators in the presence of oxygen. The reaction is carried out at 293, 550, and 700 K. Reaction products are probed by a multiplexed chemical kinetics photoionization mass spectrometer coupled with the synchrotron radiation produced at the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory. Products are identified on the basis of mass-to-charge ratio, ionization energies, and shape of photoionization spectra. Reaction pathways are proposed together with detected primary products.

The role of photoionization in negative corona discharge

Directory of Open Access Journals (Sweden)

B. X. Lu

2016-09-01

Full Text Available The effect of photoionization on the negative corona discharge was simulated based on the needle to plane air gaps. The Trichel pulse, pulse train, electron density and the distribution of electric field will be discussed in this manuscript. Effect of photoionization on the magnitude and interval of the first pulse will be discussed for different applied voltages. It is demonstrated that the peak of the first pulse current could be weakened by photoionization and a critical voltage of the first pulse interval influenced by photoionization was given.

Dissociative Photoionization of the Elusive Vinoxy Radical.

Science.gov (United States)

Adams, Jonathan D; Scrape, Preston G; Lee, Shih-Huang; Butler, Laurie J

2017-08-24

These experiments report the dissociative photoionization of vinoxy radicals to m/z = 15 and 29. In a crossed laser-molecular beam scattering apparatus, we induce C-Cl bond fission in 2-chloroacetaldehyde by photoexcitation at 157 nm. Our velocity measurements, combined with conservation of angular momentum, show that 21% of the C-Cl photofission events form vinoxy radicals that are stable to subsequent dissociation to CH 3 + CO or H + ketene. Photoionization of these stable vinoxy radicals, identified by their velocities, which are momentum-matched with the higher-kinetic-energy Cl atom photofragments, shows that the vinoxy radicals dissociatively photoionize to give signal at m/z = 15 and 29. We calibrated the partial photoionization cross section of vinoxy to CH 3 + relative to the bandwidth-averaged photoionization cross section of the Cl atom at 13.68 eV to put the partial photoionization cross sections on an absolute scale. The resulting bandwidth-averaged partial cross sections are 0.63 and 1.3 Mb at 10.5 and 11.44 eV, respectively. These values are consistent with the upper limit to the cross section estimated from a study by Savee et al. on the O( 3 P) + propene bimolecular reaction. We note that the uncertainty in these values is primarily dependent on the signal attributed to C-Cl primary photofission in the m/z = 35 (Cl + ) time-of-flight data. While the value is a rough estimate, the bandwidth-averaged partial photoionization cross section of vinoxy to HCO + calculated from the signal at m/z = 29 at 11.53 eV is approximately half that of vinoxy to CH 3 + . We also present critical points on the potential energy surface of the vinoxy cation calculated at the G4//B3LYP/6-311++G(3df,2p) level of theory to support the observation of dissociative ionization of vinoxy to both CH 3 + and HCO + .

VUV photoionization cross sections of HO2, H2O2, and H2CO.

Science.gov (United States)

Dodson, Leah G; Shen, Linhan; Savee, John D; Eddingsaas, Nathan C; Welz, Oliver; Taatjes, Craig A; Osborn, David L; Sander, Stanley P; Okumura, Mitchio

2015-02-26

The absolute vacuum ultraviolet (VUV) photoionization spectra of the hydroperoxyl radical (HO2), hydrogen peroxide (H2O2), and formaldehyde (H2CO) have been measured from their first ionization thresholds to 12.008 eV. HO2, H2O2, and H2CO were generated from the oxidation of methanol initiated by pulsed-laser-photolysis of Cl2 in a low-pressure slow flow reactor. Reactants, intermediates, and products were detected by time-resolved multiplexed synchrotron photoionization mass spectrometry. Absolute concentrations were obtained from the time-dependent photoion signals by modeling the kinetics of the methanol oxidation chemistry. Photoionization cross sections were determined at several photon energies relative to the cross section of methanol, which was in turn determined relative to that of propene. These measurements were used to place relative photoionization spectra of HO2, H2O2, and H2CO on an absolute scale, resulting in absolute photoionization spectra.

Photoionization of environmentally polluting aromatic chlorides and nitrides on the water surface by laser and synchrotron radiations.

Science.gov (United States)

Sato, Miki; Maeda, Yuki; Ishioka, Toshio; Harata, Akira

2017-11-20

The detection limits and photoionization thresholds of polycyclic aromatic hydrocarbons and their chlorides and nitrides on the water surface are examined using laser two-photon ionization and single-photon ionization, respectively. The laser two-photon ionization methods are highly surface-selective, with a high sensitivity for aromatic hydrocarbons tending to accumulate on the water surface in the natural environment due to their highly hydrophobic nature. The dependence of the detection limits of target aromatic molecules on their physicochemical properties (photoionization thresholds relating to excess energy, molar absorptivity, and the octanol-water partition coefficient) is discussed. The detection limit clearly depends on the product of the octanol-water partition coefficient and molar absorptivity, and no clear dependence was found on excess energy. The detection limits of laser two-photon ionization for these types of molecules on the water surface are formulated.

Prompt and delayed Coulomb explosion of doubly ionized hydrogen chloride molecules in intense femtosecond laser fields

Science.gov (United States)

Ma, Junyang; Li, Hui; Lin, Kang; Song, Qiying; Ji, Qinying; Zhang, Wenbin; Li, Hanxiao; Sun, Fenghao; Qiang, Junjie; Lu, Peifen; Gong, Xiaochun; Zeng, Heping; Wu, Jian

2018-06-01

We experimentally investigate the dissociative double ionization of hydrogen chloride (HCl) molecules in intense femtosecond laser pulses. In addition to the prompt dissociation channels which occur on femtosecond timescales, long-lived hydrogen chloride dications which Coulomb-explode in flight towards the detector are clearly identified in the photoion-photoion coincidence spectrum. Different pathways leading to these prompt and delayed dissociation channels involving various bound and repulsive states of the HCl dication are discussed based on the observed kinetic energy release and momentum distributions. Our results indicate that the specific features of the HCl dication potential energy curves are responsible for the generation of the delayed fragmentation channels, which are expected to be general processes for the hydrogen halides.

Resonantly enhanced collisional ionization measurements of radionuclides

International Nuclear Information System (INIS)

Whitaker, T.J.; Bushaw, B.A.; Gerke, G.K.

1986-01-01

The authors developed a new laser technique to analyze for radionuclides at extremely low levels. The technique, called resonantly enhanced collisional ionization (RECI), uses two nitrogen-laser pumped dye lasers to excite the target isotope to a high-energy Rydberg state. Atoms in these Rydberg states (within a few hundred wavenumbers in energy from the ionization threshold) efficiently ionize upon colliding with an inert gas and the ions can be detected by conventional means. The principal advantage of resonantly-enhanced collisional ionization is the extreme sensitivity coupled with its relative simplicity and low cost. Actinides typically have an ionization potential of about 6eV (uranium I.P. = 6.2 eV, plutonium I.P. = 5.7 eV). Two-step laser excitation to a state just below threshold requires wavelengths in the blue region of the visible spectrum. They showed that when both steps in the excitation process are resonant steps, relatively low-power lasers can populate the Rydberg state with almost unit efficiency. This is because the resonant excitations have much larger cross-sections than do photoionization processes. They also demonstrated that a few torr of a buffer gas will cause most of the excited-state atoms to be ionized

An alternative approach to condensed-phase photoionization

Energy Technology Data Exchange (ETDEWEB)

Ma Xiaoguang [Department of Physics, Yantai Normal University, Yantai 264025 (China)]. E-mail: hsiaoguangma@163.com

2006-01-02

Starting from Maxwell's equations for the electromagnetic field in a linear Kramers-Kronig dielectric, a general expression for photoionization cross sections of atoms or molecules embedded in a medium and a dielectric influence function (DIF) are derived in this Letter firstly. It is also suggested that a density turning point (DTP) of a photoionization process may be viewed as the critical density N{sub c}({omega}) where the photoionization properties may have notable and different variations with density.

Double photoionization of propylene oxide: A coincidence study of the ejection of a pair of valence-shell electrons

Science.gov (United States)

Falcinelli, Stefano; Vecchiocattivi, Franco; Alagia, Michele; Schio, Luca; Richter, Robert; Stranges, Stefano; Catone, Daniele; Arruda, Manuela S.; Mendes, Luiz A. V.; Palazzetti, Federico; Aquilanti, Vincenzo; Pirani, Fernando

2018-03-01

Propylene oxide, a favorite target of experimental and theoretical studies of circular dichroism, was recently discovered in interstellar space, further amplifying the attention to its role in the current debate on protobiological homochirality. In the present work, a photoelectron-photoion-photoion coincidence technique, using an ion-imaging detector and tunable synchrotron radiation in the 18.0-37.0 eV energy range, permits us (i) to observe six double ionization fragmentation channels, their relative yields being accounted for about two-thirds by the couple (C2H4+, CH2O+) and one-fifth by (C2H3+, CH3O+); (ii) to measure thresholds for their openings as a function of photon energy; and (iii) to unravel a pronounced bimodality for a kinetic-energy-released distribution, fingerprint of competitive non-adiabatic mechanisms.

Resonance ionization in a gas cell: a feasibility study for a laser ion source

International Nuclear Information System (INIS)

Qamhieh, Z.N.; Vandeweert, E.; Silverans, R.E.; Duppen, P. van; Huyse, M.; Vermeeren, L.

1992-01-01

A laser ion source based on resonance photo-ionization in a gas cell is proposed. The gas cell, filled with helium, consists of a target chamber in which the recoil products are stopped and neutralized, and an ionization chamber where the atoms of interest are selectively ionized by the laser light. The extraction of the ions from the ionization chamber through the exit hole-skimmer setup is similar to the ion-guide system. The conditions to obtain an optimal system are given. The results of a two-step one-laser resonance photo-ionization of nickel and the first results of laser ionization in a helium buffer gas cell are presented. (orig.)

Analysis of sample composition using resonant ionization and time-of-flight techniques

International Nuclear Information System (INIS)

Cruz, A. de la; Ortiz, M.; Campos, J.

1995-01-01

This paper describes the setting up of a linear time-of-flight mass spectrometer that uses a tunable laser to produce resonant ionization of atoms and molecules in a pulsed supersonic beam. The ability of this kind of systems to produce time resolved signals for each species present in the sample allows quantitative analysis of its composition. By using a tunable laser beam of high spectral resolution to produce ionization, studies based on the structure of the photoionization spectra obtained are possible. In the present work several isotopic species of ordinary and deuterated benzene have been studied. Special care has been dedicated to the influence of the presence of a 13C in the ring. In this way values for spectroscopic constants and isotopic shifts have been obtained. Another system based in a homemade proportional counter has been designed and used is an auxiliary system. The results obtained with it are independent of these mentioned above and compatible with them. This system is of great utility for laser wavelength tuning to produce ionization in the mass spectrometer. (Author) 98 refs

Analysis of sample composition using resonant ionization and time-of-flight techniques

International Nuclear Information System (INIS)

Luz, A. de la; Ortiz, M.; Campos, J.

1995-01-01

This paper describes the setting up of a linear time-of-flight mass spectrometer that uses a tunable laser to produce resonant ionization of atoms and molecules in a pulsed supersonic beam. The ability of this kind of systems to produce time resolved signals for each species present in the samples allows quantitative analysis of its composition. By using a tunable laser beam of high spectral resolution to produce ionization, studies based on the structure of the photoionization spectra obtained are possible. In the present work several isotopic species of ordinary and deuterated benzene have been studies. special care has been dedicated to the influence of the presence of a ''13 C in the ring. In this way values for spectroscopic constants and isotopic shifts have been obtained. Another system based in a homemade proportional counter has been designed and used as an auxiliary system. The results obtained with it are independent of these mentioned above and compatible with them. This system is of great utility for laser wavelength tuning to produce ionization in the mass spectrometer

On possible structures of normal ionizing shock waves in electromagnetic shock tubes

International Nuclear Information System (INIS)

Liberman, M.A.; Synakh, V.S.; Zakajdakhov, V.V.; Velikovich, A.L.

1982-01-01

The problem of possible structures of normal ionizing shock waves is studied. On the basis of the general theory of ionizing shock waves in magnetic fields, a similarity solution of the piston problem for an impenetrable piston and a magnetic piston is described and a numerical solution of the non-stationary piston problem is obtained. It is shown that precursor photo-ionization of the neutral gas by the radiation of the shock-heated gas is the dominant factor in shaping normal ionizing shock structures. In particular, it is shown that the strong overheating of atoms and ions in shock fronts is due to the tensor form of Ohm's law in the precursor region. (author)

Ionization photophysics and spectroscopy of dicyanoacetylene

Energy Technology Data Exchange (ETDEWEB)

Leach, Sydney, E-mail: Sydney.Leach@obspm.fr, E-mail: Martin.Schwell@lisa.u-pec.fr; Champion, Norbert [LERMA UMR CNRS 8112, Observatoire de Paris-Meudon, 5 place Jules-Jansen, 92195 Meudon (France); Schwell, Martin, E-mail: Sydney.Leach@obspm.fr, E-mail: Martin.Schwell@lisa.u-pec.fr; Bénilan, Yves; Fray, Nicolas; Gazeau, Marie-Claire [LISA UMR CNRS 7583, Université Paris-Est Créteil and Université Paris Diderot, Institut Pierre Simon Laplace, 61 Avenue du Général de Gaulle, 94010 Créteil (France); Garcia, Gustavo A.; Gaie-Levrel, François [Synchrotron SOLEIL, L’Orme des Merisiers, St. Aubin, B.P. 48, 91192 Gif-sur-Yvette Cedex (France); Guillemin, Jean-Claude [Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS UMR 6226, 11 Allée de Beaulieu, CS 50837, 35708 Rennes Cedex 7 (France)

2013-11-14

Photoionization of dicyanoacetylene was studied using synchrotron radiation over the excitation range 8–25 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and detailed spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of dicyanoacetylene was measured as 11.80 ± 0.01 eV. A detailed analysis of the cation spectroscopy involves new aspects and new assignments of the vibrational components to excitation of the quasi-degenerate A{sup 2}Π{sub g}, B{sup 2}Σ{sub g}{sup +} states as well as the C{sup 2}Σ{sub u}{sup +} and D{sup 2}Π{sub u} states of the cation. Some of the structured autoionization features observed in the 12.4–15 eV region of the total ion yield spectrum were assigned to vibrational components of valence shell transitions and to two previously unknown Rydberg series converging to the D{sup 2}Π{sub u} state of C{sub 4}N{sub 2}{sup +}. The appearance energies of the fragment ions C{sub 4}N{sup +}, C{sub 3}N{sup +}, C{sub 4}{sup +}, C{sub 2}N{sup +}, and C{sub 2}{sup +} were measured and their heats of formation were determined and compared with existing literature values. Thermochemical calculations of the appearance potentials of these and other weaker ions were used to infer aspects of dissociative ionization pathways.

Comparison of electrospray ionization and atmospheric pressure photoionization liquid chromatography mass spectrometry methods for analysis of ergot alkaloids from endophyte-infected sleepygrass (Achnatherum robustum).

Science.gov (United States)

Jarmusch, Alan K; Musso, Ashleigh M; Shymanovich, Tatsiana; Jarmusch, Scott A; Weavil, Miranda J; Lovin, Mary E; Ehrmann, Brandie M; Saari, Susanna; Nichols, David E; Faeth, Stanley H; Cech, Nadja B

2016-01-05

Ergot alkaloids are mycotoxins with an array of biological effects. With this study, we investigated for the first time the application of atmospheric pressure photoionization (APPI) as an ionization method for LC-MS analysis of ergot alkaloids, and compared its performance to that of the more established technique of electrospray ionization (ESI). Samples of the grass Achnatherum robustum infected with the ergot producing Epichloë fungus were extracted using cold methanol and subjected to reserved-phase HPLC-ESI-MS and HPLC-APPI-MS analysis. The ergot alkaloids ergonovine and lysergic acid amide were detected in these samples, and quantified via external calibration. Validation parameters were recorded in accordance with ICH guidelines. A triple quadrupole MS operated in multiple reaction monitoring yielded the lowest detection limits. The performance of APPI and ESI methods was comparable. Both methods were subject to very little matrix interference, with percent recoveries ranging from 82% to 100%. As determined with HPLC-APPI-MS quantification, lysergic acid amide and ergonovine were extracted from an A. robustum sample infected with the Epichloë fungus at concentrations of 1.143±0.051 ppm and 0.2822±0.0071 ppm, respectively. There was no statistically significant difference between these concentrations and those determined using ESI for the same samples. Copyright © 2015 Elsevier B.V. All rights reserved.

Atmospheric pressure photoionization using tunable VUV synchrotron radiation

International Nuclear Information System (INIS)

Giuliani, A.; Giorgetta, J.-L.; Ricaud, J.-P.; Jamme, F.; Rouam, V.; Wien, F.; Laprévote, O.; Réfrégiers, M.

2012-01-01

Highlights: ► Coupling of an atmospheric pressure photoionization source with a vacuum ultra-violet (VUV) beamline. ► The set up allows photoionization up to 20 eV. ► Compared to classical atmospheric pressure photoionization (APPI), our set up offers spectral purity and tunability. ► Allows photoionization mass spectrometry on fragile and hard to vaporize molecules. - Abstract: We report here the first coupling of an atmospheric pressure photoionization (APPI) source with a synchrotron radiation beamline in the vacuum ultra-violet (VUV). A commercial APPI source of a QStar Pulsar i from AB Sciex was modified to receive photons from the DISCO beamline at the SOLEIL synchrotron radiation facility. Photons are delivered at atmospheric pressure in the 4–20 eV range. The advantages of this new set up, termed SR-APPI, over classical APPI are spectral purity and continuous tunability. The technique may also be used to perform tunable photoionization mass spectrometry on fragile compounds difficult to vaporize by classical methods.

Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation.

Science.gov (United States)

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P; Fang, Yigang; Kostko, Oleg; Ahmed, Musahid; Head-Gordon, Martin

2017-05-23

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C 2 H 2 ) n + , just like ionized acetylene clusters. The fragmentation products result from reactive ion-molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C 4 H 4 + and C 6 H 6 + structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C 2 H 2 ) n + isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C 6 H 6 + isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.

Ab initio dynamics and photoionization mass spectrometry reveal ion–molecule pathways from ionized acetylene clusters to benzene cation

Science.gov (United States)

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P.; Fang, Yigang; Kostko, Oleg

2017-01-01

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion–molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C2H2)n+, just like ionized acetylene clusters. The fragmentation products result from reactive ion–molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C4H4+ and C6H6+ structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C2H2)n+ isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C6H6+ isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM. PMID:28484019

Dissociative photoionization of 1,3-butadiene: experimental and theoretical insights.

Science.gov (United States)

Fang, Wenzheng; Gong, Lei; Zhang, Qiang; Shan, Xiaobin; Liu, Fuyi; Wang, Zhenya; Sheng, Liusi

2011-05-07

The vacuum-ultraviolet photoionization and dissociative photoionization of 1,3-butadiene in a region ∼8.5-17 eV have been investigated with time-of-flight photoionization mass spectrometry using tunable synchrotron radiation. The adiabatic ionization energy of 1,3-butadiene and appearance energies for its fragment ions, C(4)H(5)(+), C(4)H(4)(+), C(4)H(3)(+), C(3)H(3)(+), C(2)H(4)(+), C(2)H(3)(+), and C(2)H(2)(+), are determined to be 9.09, 11.72, 13.11, 15.20, 11.50, 12.44, 15.15, and 15.14 eV, respectively, by measurements of photoionization efficiency spectra. Ab initio molecular orbital calculations have been performed to investigate the reaction mechanism of dissociative photoionization of 1,3-butadiene. On the basis of experimental and theoretical results, seven dissociative photoionization channels are proposed: C(4)H(5)(+) + H, C(4)H(4)(+) + H(2), C(4)H(3)(+) + H(2) + H, C(3)H(3)(+) + CH(3), C(2)H(4)(+) + C(2)H(2), C(2)H(3)(+) + C(2)H(2) + H, and C(2)H(2)(+) + C(2)H(2) + H(2). Channel C(3)H(3)(+) + CH(3) is found to be the dominant one, followed by C(4)H(5)(+) + H and C(2)H(4)(+) + C(2)H(2). The majority of these channels occur via isomerization prior to dissociation. Transition structures and intermediates for those isomerization processes were also determined.

Progress on resonance ionization detection of combustion radicals

International Nuclear Information System (INIS)

Cool, T.A.

1994-01-01

Selective laser ionization techniques are used in our laboratory for the measurement of concentration profiles of radical intermediates in the combustion of chlorinated hydrocarbon flames. A new ultrasensitive detection technique, made possible with the advent of tunable VUV laser sources, enables the selective near-threshold photoionization of all radical intermediates in premixed hydrocarbon and chlorinated hydrocarbon flames. The progress made on the following three separate experiments during the past year is briefly described in this report. Flame Radical Concentration Measurements with VUV Spectroscopy; observation of hyperfine quantum beats in cyanogen; and the spectroscopy of the ClCO radical

Photoionization and electron-ion recombination of Cr I

International Nuclear Information System (INIS)

Nahar, Sultana N.

2009-01-01

Using the unified method, the inverse processes of photoionization and electron-ion recombination are studied in detail for neutral chromium, (CrI+hν↔CrII+e), for the ground and excited states. The unified method based on close-coupling approximation and R-matrix method (i) subsumes both the radiative recombination (RR) and dielectronic recombination (DR) for the total rate and (ii) provides self-consistent sets of photoionization cross sections σ PI and recombination rates α RC . The present results show in total photoionization of the ground and excited states an enhancement in the background at the first excited threshold, 3d 4 4s 5 D state of the core. One prominent phot-excitation-of-core (PEC) resonance due to one dipole allowed transition ( 6 S- 6 P o ) in the core is found in the photoionization cross sections of most of the valence electron excited states. Structures in the total and partial photoionization, for ionization into various excited core states and ground state only, respectively, are demonstrated. Results are presented for the septet and quintet states with n≤10 and l≤9 of Cr I. These states couple to the core ground state 6 S and contribute to the recombination rates. State-specific recombination rates are also presented for these states and their features are illustrated. The total recombination rate shows two DR peaks, one at a relatively low temperature, at 630 K, and the other around 40,000 K. This can explain existence of neutral Cr in interstellar medium. Calculations were carried out in LS coupling using a close-coupling wave function expansion of 40 core states. The results illustrate the features in the radiative processes of Cr I and provide photoionization cross sections and recombination rates with good approximation for this astrophysically important ion.

Population of the 3P2,1,0 fine-structure states in the 3s and 3p photoionization of atomic chlorine

International Nuclear Information System (INIS)

Krause, M.O.; Caldwell, C.D.; Whitfield, S.B.; de Lange, C.A.; van der Meulen, P.

1993-01-01

In a high-resolution photoelectron-spectrometry study of the photoionization of chlorine atoms in both the 3s and 3p subshells, we were able to resolve contributions from ionic states with specific J values and measure the relative populations of these fine-structure components. Our photoelectron spectra, recorded at hν=29.2 eV, give ratios of 3 P 2 : 3 P 1 : 3 P 0 =100:40.59.5 for 3p photoionization and 3 P 2 : 3 P 1 =100:31 for 3s photoionization. While the results for 3p ionization are in accord with predictions based on a simple geometric analysis, the contribution of the 3 P 1 state in 3s photoionization is larger than that predicted by this simple model. The geometric predictions are also compared with results from a similar measurement of the population of the 4p -1 ( 3 P J ) states produced in the 4p ionization of Br and with earlier work on the production of 3 D 2,1,0 states in d-shell photoionization of Cu and Ag

The Monte Carlo photoionization and moving-mesh radiation hydrodynamics code CMACIONIZE

Science.gov (United States)

Vandenbroucke, B.; Wood, K.

2018-04-01

We present the public Monte Carlo photoionization and moving-mesh radiation hydrodynamics code CMACIONIZE, which can be used to simulate the self-consistent evolution of HII regions surrounding young O and B stars, or other sources of ionizing radiation. The code combines a Monte Carlo photoionization algorithm that uses a complex mix of hydrogen, helium and several coolants in order to self-consistently solve for the ionization and temperature balance at any given type, with a standard first order hydrodynamics scheme. The code can be run as a post-processing tool to get the line emission from an existing simulation snapshot, but can also be used to run full radiation hydrodynamical simulations. Both the radiation transfer and the hydrodynamics are implemented in a general way that is independent of the grid structure that is used to discretize the system, allowing it to be run both as a standard fixed grid code, but also as a moving-mesh code.

Photoionization of furan from the ground and excited electronic states.

Science.gov (United States)

Ponzi, Aurora; Sapunar, Marin; Angeli, Celestino; Cimiraglia, Renzo; Došlić, Nađa; Decleva, Piero

2016-02-28

Here we present a comparative computational study of the photoionization of furan from the ground and the two lowest-lying excited electronic states. The study aims to assess the quality of the computational methods currently employed for treating bound and continuum states in photoionization. For the ionization from the ground electronic state, we show that the Dyson orbital approach combined with an accurate solution of the continuum one particle wave functions in a multicenter B-spline basis, at the density functional theory (DFT) level, provides cross sections and asymmetry parameters in excellent agreement with experimental data. On the contrary, when the Dyson orbitals approach is combined with the Coulomb and orthogonalized Coulomb treatments of the continuum, the results are qualitatively different. In excited electronic states, three electronic structure methods, TDDFT, ADC(2), and CASSCF, have been used for the computation of the Dyson orbitals, while the continuum was treated at the B-spline/DFT level. We show that photoionization observables are sensitive probes of the nature of the excited states as well as of the quality of excited state wave functions. This paves the way for applications in more complex situations such as time resolved photoionization spectroscopy.

Emission spectra of photoionized plasmas induced by intense EUV pulses: Experimental and theoretical investigations

Science.gov (United States)

Saber, Ismail; Bartnik, Andrzej; Skrzeczanowski, Wojciech; Wachulak, Przemysław; Jarocki, Roman; Fiedorowicz, Henryk

2017-03-01

Experimental measurements and numerical modeling of emission spectra in photoionized plasma in the ultraviolet and visible light (UV/Vis) range for noble gases have been investigated. The photoionized plasmas were created using laser-produced plasma (LPP) extreme ultraviolet (EUV) source. The source was based on a gas puff target; irradiated with 10ns/10J/10Hz Nd:YAG laser. The EUV radiation pulses were collected and focused using grazing incidence multifoil EUV collector. The laser pulses were focused on a gas stream, injected into a vacuum chamber synchronously with the EUV pulses. Irradiation of gases resulted in a formation of low temperature photoionized plasmas emitting radiation in the UV/Vis spectral range. Atomic photoionized plasmas produced this way consisted of atomic and ionic with various ionization states. The most dominated observed spectral lines originated from radiative transitions in singly charged ions. To assist in a theoretical interpretation of the measured spectra, an atomic code based on Cowan's programs and a collisional-radiative PrismSPECT code have been used to calculate the theoretical spectra. A comparison of the calculated spectral lines with experimentally obtained results is presented. Electron temperature in plasma is estimated using the Boltzmann plot method, by an assumption that a local thermodynamic equilibrium (LTE) condition in the plasma is validated in the first few ionization states. A brief discussion for the measured and computed spectra is given.

Double Photoionization Near Threshold

Science.gov (United States)

Wehlitz, Ralf

2007-01-01

The threshold region of the double-photoionization cross section is of particular interest because both ejected electrons move slowly in the Coulomb field of the residual ion. Near threshold both electrons have time to interact with each other and with the residual ion. Also, different theoretical models compete to describe the double-photoionization cross section in the threshold region. We have investigated that cross section for lithium and beryllium and have analyzed our data with respect to the latest results in the Coulomb-dipole theory. We find that our data support the idea of a Coulomb-dipole interaction.

Ionization of a two-electron atom in a strong electromagnetic field

International Nuclear Information System (INIS)

Ovodova, O.V.; Popov, A.M.; Tikhonova, O.V.

1997-01-01

A one-dimensional model of a helium atom in an intense field of a femtosecond electromagnetic pulse has been constructed using the Hartree technique. 'Exact' calculations have been compared to the approximations of 'frozen' and 'passive' electrons. A nonmonotonic dependence of the single-electron ionization probability on the radiation intensity has been detected. Minima in the ionization probability are due to multiphoton resonances between different atomic states due to the dynamic Stark effect. We suggest that the ionization suppression is due to the interference stabilization in this case

Tachyonic ionization cross sections of hydrogenic systems

Energy Technology Data Exchange (ETDEWEB)

Tomaschitz, Roman [Department of Physics, Hiroshima University, 1-3-1 Kagami-yama, Higashi-Hiroshima 739-8526 (Japan)

2005-03-11

Transition rates for induced and spontaneous tachyon radiation in hydrogenic systems as well as the transversal and longitudinal ionization cross sections are derived. We investigate the interaction of the superluminal radiation field with matter in atomic bound-bound and bound-free transitions. Estimates are given for Ly-{alpha} transitions effected by superluminal quanta in hydrogen-like ions. The tachyonic photoelectric effect is scrutinized, in the Born approximation and at the ionization threshold. The angular maxima occur at different scattering angles in the transversal and longitudinal cross sections, which can be used to sift out longitudinal tachyonic quanta in a photon flux. We calculate the tachyonic ionization and recombination cross sections for Rydberg states and study their asymptotic scaling with respect to the principal quantum number. At the ionization threshold of highly excited states of order n {approx} 10{sup 4}, the longitudinal cross section starts to compete with photoionization, in recombination even at lower levels.

Photoionization of multiply charged ions at the advanced light source

International Nuclear Information System (INIS)

Schlachter, A.S.; Kilcoyne, A.L.D.; Aguilar, A.; Gharaibeh, M.F.; Emmons, E.D.; Scully, S.W.J.; Phaneuf, R.A.; Muller, A.; Schippers, S.; Alvarez, I.; Cisneros, C.; Hinojosa, G.; McLaughlin, B.M.

2004-01-01

Photoionization of multiply charged ions is studied using the merged-beams technique at the Advanced Light Source. Absolute photoionization cross sections have been measured for a variety of ions along both isoelectronic and isonuclear sequences

Photoelectron angular distributions from strong-field ionization of oriented molecules

DEFF Research Database (Denmark)

Holmegaard, Lotte; Hansen, Jonas Lerche; Kalhøj, Line

2010-01-01

The combination of ultrafast light sources with detection of molecular-frame photoelectron angular distributions (MFPADs) is setting new standards for detailed interrogation of molecular dynamics. However, until recently measurement of MFPADs relied on determining the molecular orientation after...... ionization, which is limited to species and processes where ionization leads to fragmentation. An alternative is to fix the molecular frame before ionization. The only demonstrations of such spatial orientation involved aligned small linear nonpolar molecules. Here we extend these techniques to the general...... class of polar molecules. Carbonylsulphide and benzonitrile molecules, fixed in space by combined laser and electrostatic fields, are ionized with intense, circularly polarized 30-fs laser pulses. For carbonylsulphide and benzonitrile oriented in one dimension, the MFPADs exhibit pronounced anisotropies...

Atom ionization in a nonclassical intense electromagnetic field

International Nuclear Information System (INIS)

Popov, A.M.; Tikhonova, O.V.

2002-01-01

The atoms ionization process in the intense nonclassical electromagnetic field is considered. It is shown that depending on the field quantum state the probability of ionization may essentially change even by one and the same average quantum number in the radiation mode, whereby the difference in the ionization rates is especially significant in the case, when the ionization process is of a multiphoton character. It is demonstrates in particular, that the nonclassical field may be considerably more intensive from the viewpoint of the atoms ionization, than the classical field with the same intensity. The peculiarities of the decay, related to the atomic system state in the strong nonclassical field beyond the perturbation theory frames are studied [ru

Laser resonance ionization scheme development for tellurium and germanium at the dual Ti:Sa–Dye ISOLDE RILIS

CERN Document Server

Day Goodacre, T.; Fedosseev, V.N.; Forster, L.; Marsh, B.A.; Rossel, R.E.; Rothe, S.; Veinhard, M.

2016-01-01

The resonance ionization laser ion source (RILIS) is the principal ion source of the ISOLDE radioactive beam facility based at CERN. Using the method of in-source laser resonance ionization spectroscopy, a transition to a new autoionizing state of tellurium was discovered and applied as part of a three-step, three-resonance, photo-ionization scheme. In a second study, a three-step, two-resonance, photo-ionization scheme for germanium was developed and the ionization efficiency was measured at ISOLDE. This work increases the range of ISOLDE RILIS ionized beams to 31 elements. Details of the spectroscopy studies are described and the new ionization schemes are summarized.

Laser resonance ionization scheme development for tellurium and germanium at the dual Ti:Sa–Dye ISOLDE RILIS

Energy Technology Data Exchange (ETDEWEB)

Day Goodacre, T., E-mail: thomas.day.goodacre@cern.ch [CERN, CH-1211 Geneva 23 (Switzerland); School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL (United Kingdom); Fedorov, D. [Petersburg Nuclear Physics Institute, 188350 Gatchina (Russian Federation); Fedosseev, V.N.; Forster, L.; Marsh, B.A. [CERN, CH-1211 Geneva 23 (Switzerland); Rossel, R.E. [CERN, CH-1211 Geneva 23 (Switzerland); Institut für Physik, Johannes Gutenberg Universität, D-55099 Mainz (Germany); Faculty of Design, Computer Science and Media, Hochschule RheinMain, Wiesbaden (Germany); Rothe, S.; Veinhard, M. [CERN, CH-1211 Geneva 23 (Switzerland)

2016-09-11

The resonance ionization laser ion source (RILIS) is the principal ion source of the ISOLDE radioactive beam facility based at CERN. Using the method of in-source laser resonance ionization spectroscopy, a transition to a new autoionizing state of tellurium was discovered and applied as part of a three-step, three-resonance, photo-ionization scheme. In a second study, a three-step, two-resonance, photo-ionization scheme for germanium was developed and the ionization efficiency was measured at ISOLDE. This work increases the range of ISOLDE RILIS ionized beams to 31 elements. Details of the spectroscopy studies are described and the new ionization schemes are summarized.

New photoionization lasers pumped by laser-induced plasma radiation

International Nuclear Information System (INIS)

Hube, M.; Dieckmann, M.; Beigang, R.; Welling, H.; Wellegehausen, B.

1988-01-01

Innershell photoionization of atomic gases and vapors by soft x rays from a laser-produced plasma is a potential method for making lasers at short wavelengths. Normally, in such experiments only a single plasma spot or plasma line is created for the excitation. This gives high excitation rates but only a short excitation length. At high excitation rates detrimental influences, such as amplified spontaneous emission, optical saturation, or quenching processes, may decrease or even destroy a possible inversion. Therefore, it seems to be more favorable to use a number of separated plasma spots with smaller excitation rates and larger excitation lengths. As a test, a three-plasma spot device was constructed and used in the well-known Cd-photoionization laser at 442 nm. With a 600-mJ Nd:YAH laser (pulse length, 8 ns) for plasma production, output energies up to 300 μJ have been measured, which is more than a doubling of so far obtained data. On innershell excitation, levels may be populated that allow direct lasers as in the case of Cd or that are metastable and cannot be directly coupled to lower levels. In this case modifications in the excitation process are necessary. Such modifications may be an optical pump process in the atom prior to the innershell photoionization or an optical pump process (population transfer process) after the innershell ionization, leading to Raman or anti-Stokes Raman-type laser emissions. With these techniques and the developed multiplasma spot excitation device a variety of new laser emissions in K and Cs ions have been achieved which are indicated in the level schemes

Modeling photoionization of aqueous DNA and its components.

Science.gov (United States)

Pluhařová, Eva; Slavíček, Petr; Jungwirth, Pavel

2015-05-19

Radiation damage to DNA is usually considered in terms of UVA and UVB radiation. These ultraviolet rays, which are part of the solar spectrum, can indeed cause chemical lesions in DNA, triggered by photoexcitation particularly in the UVB range. Damage can, however, be also caused by higher energy radiation, which can ionize directly the DNA or its immediate surroundings, leading to indirect damage. Thanks to absorption in the atmosphere, the intensity of such ionizing radiation is negligible in the solar spectrum at the surface of Earth. Nevertheless, such an ionizing scenario can become dangerously plausible for astronauts or flight personnel, as well as for persons present at nuclear power plant accidents. On the beneficial side, ionizing radiation is employed as means for destroying the DNA of cancer cells during radiation therapy. Quantitative information about ionization of DNA and its components is important not only for DNA radiation damage, but also for understanding redox properties of DNA in redox sensing or labeling, as well as charge migration along the double helix in nanoelectronics applications. Until recently, the vast majority of experimental and computational data on DNA ionization was pertinent to its components in the gas phase, which is far from its native aqueous environment. The situation has, however, changed for the better due to the advent of photoelectron spectroscopy in liquid microjets and its most recent application to photoionization of aqueous nucleosides, nucleotides, and larger DNA fragments. Here, we present a consistent and efficient computational methodology, which allows to accurately evaluate ionization energies and model photoelectron spectra of aqueous DNA and its individual components. After careful benchmarking, the method based on density functional theory and its time-dependent variant with properly chosen hybrid functionals and polarizable continuum solvent model provides ionization energies with accuracy of 0.2-0.3 e

Internal energy selection in vacuum ultraviolet photoionization of ethanol and ethanol dimers

Science.gov (United States)

Bodi, Andras

2013-10-01

Internal energy selected ethanol monomer and ethanol dimer ions were prepared by threshold photoionization of a supersonic molecular beam seeded with ethanol. The dissociative photoionization processes of the monomer, the lowest-energy CH3-loss channel of the dimer, and the fragmentation of larger clusters were found to be disjunct from the ionization onset to about 12 eV, which made it possible to determine the 0 K appearance energy of C-C bond breaking in the H-donor unit of the ethanol dimer cation as 9.719 ± 0.004 eV. This reaction energy is used together with ab initio calculations in a thermochemical cycle to determine the binding energy change from the neutral ethanol dimer to a protonated ethanol-formaldehyde adduct. The cycle also shows general agreement between experiment, theory, and previously published enthalpies of formation. The role of the initial ionization site, or rather the initial photoion state, is also discussed based on the dimer breakdown diagram and excited state calculations. There is no evidence for isolated state behavior, and the ethanol dimer dissociative photoionization processes appear to be governed by statistical theory and the ground electronic state of the ion. In the monomer breakdown diagram, the smoothly changing branching ratio between H and CH3 loss is at odds with rate theory predictions, and shows that none of the currently employed few-parameter rate models, appropriate for experimental rate curve fitting, yields a correct description for this process in the experimental energy range.

Rovibronically selected and resolved two-color laser photoionization and photoelectron study of cobalt carbide cation.

Science.gov (United States)

Huang, Huang; Chang, Yih Chung; Luo, Zhihong; Shi, Xiaoyu; Lam, Chow-Shing; Lau, Kai-Chung; Ng, C Y

2013-03-07

We have conducted a two-color visible-ultraviolet (VIS-UV) resonance-enhanced laser photoionization efficiency and pulsed field ionization-photoelectron (PFI-PE) study of gaseous cobalt carbide (CoC) near its ionization onset in the total energy range of 61,200-64,510 cm(-1). The cold gaseous CoC sample was prepared by a laser ablation supersonically cooled beam source. By exciting CoC molecules thus generated to single N' rotational levels of the intermediate CoC∗((2)Σ(+); v') state using a VIS dye laser prior to UV laser photoionization, we have obtained N(+) rotationally resolved PFI-PE spectra for the CoC(+)(X(1)Σ(+); v(+) = 0 and 1) ion vibrational bands free from interference by impurity species except Co atoms produced in the ablation source. The rotationally selected and resolved PFI-PE spectra have made possible unambiguous rotational assignments, yielding accurate values for the adiabatic ionization energy of CoC(X(2)Σ(+)), IE(CoC) = 62,384.3 ± 0.6 cm(-1) (7.73467 ± 0.00007 eV), the vibrational frequency ωe (+) = 985.6 ± 0.6 cm(-1), the anharmonicity constant ωe (+)χe (+) = 6.3 ± 0.6 cm(-1), the rotational constants (Be (+) = 0.7196 ± 0.0005 cm(-1), αe (+) = 0.0056 ± 0.0008 cm(-1)), and the equilibrium bond length re (+) = 1.534 Å for CoC(+)(X(1)Σ(+)). The observation of the N(+) = 0 level in the PFI-PE measurement indicates that the CoC(+) ground state is of (1)Σ(+) symmetry. Large ΔN(+) = N(+) - N' changes up to 6 are observed for the photoionization transitions CoC(+)(X(1)Σ(+); v(+) = 0-2; N(+)) ← CoC∗((2)Σ(+); v'; N' = 6, 7, 8, and 9). The highly precise energetic and spectroscopic data obtained in the present study have served as a benchmark for testing theoretical predictions based on state-of-the-art ab initio quantum calculations at the CCSDTQ∕CBS level of theory as presented in the companion article.

Electron Interference in Molecular Circular Polarization Attosecond XUV Photoionization

Directory of Open Access Journals (Sweden)

Kai-Jun Yuan

2015-01-01

Full Text Available Two-center electron interference in molecular attosecond photoionization processes is investigated from numerical solutions of time-dependent Schrödinger equations. Both symmetric H\\(_2^+\\ and nonsymmetric HHe\\(^{2+}\\ one electron diatomic systems are ionized by intense attosecond circularly polarized XUV laser pulses. Photoionization of these molecular ions shows signature of interference with double peaks (minima in molecular attosecond photoelectron energy spectra (MAPES at critical angles \\(\\vartheta_c\\ between the molecular \\(\\textbf{R}\\ axis and the photoelectron momentum \\(\\textbf{p}\\. The interferences are shown to be a function of the symmetry of electronic states and the interference patterns are sensitive to the molecular orientation and pulse polarization. Such sensitivity offers possibility for imaging of molecular structure and orbitals.

Determination of photoionization cross-sections of different organic molecules using gas chromatography coupled to single-photon ionization (SPI) time-of-flight mass spectrometry (TOF-MS) with an electron-beam-pumped rare gas excimer light source (EBEL): influence of molecular structure and analytical implications.

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Eschner, Markus S; Zimmermann, Ralf

2011-07-01

This work describes a fast and reliable method for determination of photoionization cross-sections (PICS) by means of gas chromatography (GC) coupled to single-photon ionization mass spectrometry (SPI-MS). Photoionization efficiency (PIE) data for 69 substances was obtained at a photon energy of 9.8 ± 0.4 eV using an innovative electron-beam-pumped rare gas excimer light source (EBEL) filled with argon. The investigated analytes comprise 12 alkylbenzenes as well as 11 other substituted benzenes, 23 n-alkanes, ten polyaromatic hydrocarbons, seven aromatic heterocycles, and six polyaromatic heterocycles. Absolute PICS for each substance at 9.8 eV are calculated from the relative photoionization efficiencies of the compounds with respect to benzene, whose photoionization cross-section data is well known. Furthermore, a direct correlation between the type of benzene substituents and their absolute PICS is presented and discussed in depth. Finally, comparison of previously measured photoionization cross-sections for 20 substances shows good agreement with the data of the present work.

Gas chromatography coupled to atmospheric pressure ionization mass spectrometry (GC-API-MS): review.

Science.gov (United States)

Li, Du-Xin; Gan, Lin; Bronja, Amela; Schmitz, Oliver J

2015-09-03

Although the coupling of GC/MS with atmospheric pressure ionization (API) has been reported in 1970s, the interest in coupling GC with atmospheric pressure ion source was expanded in the last decade. The demand of a "soft" ion source for preserving highly diagnostic molecular ion is desirable, as compared to the "hard" ionization technique such as electron ionization (EI) in traditional GC/MS, which fragments the molecule in an extensive way. These API sources include atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), atmospheric pressure laser ionization (APLI), electrospray ionization (ESI) and low temperature plasma (LTP). This review discusses the advantages and drawbacks of this analytical platform. After an introduction in atmospheric pressure ionization the review gives an overview about the history and explains the mechanisms of various atmospheric pressure ionization techniques used in combination with GC such as APCI, APPI, APLI, ESI and LTP. Also new developments made in ion source geometry, ion source miniaturization and multipurpose ion source constructions are discussed and a comparison between GC-FID, GC-EI-MS and GC-API-MS shows the advantages and drawbacks of these techniques. The review ends with an overview of applications realized with GC-API-MS. Copyright © 2015. Published by Elsevier B.V.

Vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters

International Nuclear Information System (INIS)

Ahmed, Musahid; Ahmed, Musahid; Wilson, Kevin R.; Belau, Leonid; Kostko, Oleg

2008-01-01

In this work we report on the vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters. Clusters of methanol with water are generated via co-expansion of the gas phase constituents in a continuous supersonic jet expansion of methanol and water seeded in Ar. The resulting clusters are investigated by single photon ionization with tunable vacuum ultraviolet synchrotron radiation and mass analyzed using reflectron mass spectrometry. Protonated methanol clusters of the form (CH3OH)nH + (n=1-12) dominate the mass spectrum below the ionization energy of the methanol monomer. With an increase in water concentration, small amounts of mixed clusters of the form (CH3OH)n(H2O)H + (n=2-11) are detected. The only unprotonated species observed in this work are the methanol monomer and dimer. Appearance energies are obtained from the photoionization efficiency (PIE) curves for CH3OH +, (CH 3OH)2 +, (CH3OH)nH + (n=1-9), and (CH 3OH)n(H2O)H + (n=2-9 ) as a function of photon energy. With an increase in the water content in the molecular beam, there is an enhancement of photoionization intensity for methanol dimer and protonated methanol monomer at threshold. These results are compared and contrasted to previous experimental observations

High sensitivity detection of desorbed biomolecules by photoionization with tunable VUV

International Nuclear Information System (INIS)

Moore, J.F.; Calaway, W.F.; Veryovkin, I.V.; Pellin, M.J.; Lewellen, J.W.; Li, Y.; Milton, S.V.; King, B.V.

2004-01-01

Full text: The spectral region from 7 to 11eV has two attributes that make it attractive for biomolecule photoionization: 1. high photoionization cross sections, leading to high detection efficiency, and 2. overlap with nearly all first ionization energies of biomolecules, allowing possible control over fragmentation by accessing different final states via tuning. The lack of available tunable lasers in this energy range has generally hindered exploitation of these features thus far. A free-electron laser in operation at Argonne National Laboratory provides high pulse energy, widely tunable VUV pulses of 300 fs duration. Coupled with a novel time-of-flight mass spectrometer, this laser is able to photoionize and detect biomolecules, including peptides and nucleosides. Either laser desorption or primary ion beams are used to desorb sample material, followed by photoionization with a VUV laser. The instrument uses novel ion optics to extract photoions from a large volume while maintaining high mass resolution. This approach is capable of yielding dramatically improved detection limits over more conventional methods such as MALDI and SIMS. In the case of the common peptide substance P, for example, a substantial improvement over the MALDI signal was observed using VUV photoionization with very little observed fragmentation of the molecule. Nucleosides and cisplatin were also measured with typically order of magnitude improvements in signal. These and other examples show clearly the benefits that can be obtained in high sensitivity mass spectrometry of biomolecules with the increasing availability of VUV laser sources

Effects of screened Coulomb (Yukawa) and exponential-cosine-screened Coulomb potentials on photoionization of H and He+

International Nuclear Information System (INIS)

Lin, C.Y.; Ho, Y.K.

2010-01-01

The screening effects due to the exponential-cosine-screened Coulomb and screened Coulomb (Yukawa) potentials on photoionization processes are explored within the framework of complex coordinate rotation method. The energy levels of H and He + in both screened potentials shifted with various Debye screening lengths are presented. The photoionization cross sections illustrate the considerable screening effects on photoionization processes in low energy region. The shape resonances can be found near ionization thresholds for certain of Debye screening lengths. The relations between the appearance of resonances and the existence of quasi-bound states under shielding conditions are discussed. (authors)

Effective temperature of an ultracold electron source based on near-threshold photoionization.

Science.gov (United States)

Engelen, W J; Smakman, E P; Bakker, D J; Luiten, O J; Vredenbregt, E J D

2014-01-01

We present a detailed description of measurements of the effective temperature of a pulsed electron source, based on near-threshold photoionization of laser-cooled atoms. The temperature is determined by electron beam waist scans, source size measurements with ion beams, and analysis with an accurate beam line model. Experimental data is presented for the source temperature as a function of the wavelength of the photoionization laser, for both nanosecond and femtosecond ionization pulses. For the nanosecond laser, temperatures as low as 14 ± 3 K were found; for femtosecond photoionization, 30 ± 5 K is possible. With a typical source size of 25 μm, this results in electron bunches with a relative transverse coherence length in the 10⁻⁴ range and an emittance of a few nm rad. © 2013 Elsevier B.V. All rights reserved.

Photoionization sensors for non-invasive medical diagnostics

Science.gov (United States)

Mustafaev, Aleksandr; Rastvorova, Iuliia; Khobnya, Kristina; Podenko, Sofia

2016-09-01

The analysis of biomarkers can help to identify the significant number of diseases: lung cancer, tuberculosis, diabetes, high levels of stress, psychosomatic disorders etc. To implement continuous monitoring of the state of human health, compact VUV photoionization detector with current-voltage measurement is designed by Saint-Petersburg Mining University Plasma Research Group. This sensor is based on the patented method of stabilization of electric parameters - CES (Collisional Electron Spectroscopy). During the operation at atmospheric pressure VUV photoionization sensor measures the energy of electrons, produced in the ionization with the resonance photons, whose wavelength situated in the vacuum ultraviolet (VUV). A special software was developed to obtain the second-order derivative of the I-U characteristics, taken by the VUV sensor, to construct the energy spectra of the characteristic electrons. VUV photoionization detector has an unique set of parameters: small size (10*10*1 mm), low cost, wide range of recognizable molecules, as well as accuracy, sufficient for using this instrument for the medical purposes. This device can be used for non-invasive medical diagnostics without compromising the quality of life, for control of environment and human life. Work supported by Foundation for Assistance to Small Innovative Enterprises in Science and Technology.

Flash photoionization of gamma-ray burst environments

Science.gov (United States)

Band, David L.; Hartmann, Dieter H.

1992-01-01

The H-alpha line emission that a flash-photoionized region emits is calculated. Archival transients, as well as various theoretical predictions, suggest that there may be significant ionizing flux. The limits on the line flux which might be observable indicate that the density must be fairly high for the recombination radiation to be observable. The intense burst radiation is insufficient to melt the dust which will be present in such a dense medium. This dust may attenuate the observable line emission, but does not attenuate the ionizing radiation before it ionizes the neutral medium surrounding the burst source. The dust can also produce a light echo. If there are indeed gamma-ray bursts in dense clouds, then it is possible that the burst was triggered by Bondi-Hoyle accretion from the dense medium, although it is unlikely on statistical grounds that all bursts occur in clouds.

Adaptive finite-element ballooning analysis of bipolar ionized fields

International Nuclear Information System (INIS)

Al-Hamouz, Z.M.

1995-01-01

This paper presents an adaptive finite-element iterative method for the analysis of the ionized field around high-voltage bipolar direct-current (HVDC) transmission line conductors without resort to Deutsch's assumption. A new iterative finite-element ballooning technique is proposed to solve Poisson's equation wherein the commonly used artificial boundary around the transmission line conductors is simulated at infinity. Unlike all attempts reported in the literature for the solution of ionized field, the constancy of the conductors' surface field at the corona onset value is directly implemented in the finite-element formulation. In order to investigate the effectiveness of the proposed method, a laboratory model was built. It has been found that the calculated V-I characteristics and the ground-plane current density agreed well with those measured experimentally. The simplicity in computer programming in addition to the low number of iterations required to achieve convergence characterize this method of analysis

Ionic fragmentation following core-level photoionization of Sn(CH3)4 by soft X-rays

International Nuclear Information System (INIS)

Ueda, Kiyoshi; Shigemasa, Eiji; Sato, Yukinori; Yagishita, Akira; Hayaishi, Tatsuji

1990-01-01

Ionic fragmentation following the photoionization of Sn(CH 3 ) 4 (TMT) has been studied in the photon energy range of 60-600 eV using synchrotron radiation and time-of-flight mass spectrometry. Each of the Sn:4d, 4p, 3d and C:1s photoionization leads to a type of ionic fragmentation that is characteristic of each ionized core. The Sn:4d photoionization above 60 eV predominantly produces the doubly-charged TMT which dissociates into two singly-charged ions and some neutral fragments. The ions produced in this pathway are CH 3 + , C 2 H 3 + , C 2 H 5 + , SnCH m + and/or Sn + . The Sn:4p photoionization produces the triply-charged TMT and enhances the production of H + , CHsub(m' + ) (m' = 0-3) and Sn + significantly. The Sn:3d photoionization produces multiply-charged TMT whose charges are 3-5 and enhances the production of H + , CHsub(m' + ) (m' = 0-2) and Sn + significantly. The C:1s photoionization produces doubly-charged TMT via the KVV Auger transition and enhances the production of CH 3 + , C 2 H 3 + , SnCH m + and/or Sn + . (orig.)

Gadolinium photoionization process

Science.gov (United States)

Paisner, Jeffrey A.; Comaskey, Brian J.; Haynam, Christopher A.; Eggert, Jon H.

1993-01-01

A method is provided for selective photoionization of the odd-numbered atomic mass gadolinium isotopes 155 and 157. The selective photoionization is accomplished by circular or linear parallel polarized laser beam energy effecting a three-step photoionization pathway.

Surface-assisted laser desorption ionization mass spectrometry techniques for application in forensics.

Science.gov (United States)

Guinan, Taryn; Kirkbride, Paul; Pigou, Paul E; Ronci, Maurizio; Kobus, Hilton; Voelcker, Nicolas H

2015-01-01

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) is an excellent analytical technique for the rapid and sensitive analysis of macromolecules (>700 Da), such as peptides, proteins, nucleic acids, and synthetic polymers. However, the detection of smaller organic molecules with masses below 700 Da using MALDI-MS is challenging due to the appearance of matrix adducts and matrix fragment peaks in the same spectral range. Recently, nanostructured substrates have been developed that facilitate matrix-free laser desorption ionization (LDI), contributing to an emerging analytical paradigm referred to as surface-assisted laser desorption ionization (SALDI) MS. Since SALDI enables the detection of small organic molecules, it is rapidly growing in popularity, including in the field of forensics. At the same time, SALDI also holds significant potential as a high throughput analytical tool in roadside, work place and athlete drug testing. In this review, we discuss recent advances in SALDI techniques such as desorption ionization on porous silicon (DIOS), nano-initiator mass spectrometry (NIMS) and nano assisted laser desorption ionization (NALDI™) and compare their strengths and weaknesses with particular focus on forensic applications. These include the detection of illicit drug molecules and their metabolites in biological matrices and small molecule detection from forensic samples including banknotes and fingerprints. Finally, the review highlights recent advances in mass spectrometry imaging (MSI) using SALDI techniques. © 2014 Wiley Periodicals, Inc.

Non-Liouvillean ion injection via resonantly enhanced two-photon ionization

Directory of Open Access Journals (Sweden)

B. A. Knyazev

2004-03-01

Full Text Available The charge-exchange method is now one of the main techniques for ion injection into accelerators and storage rings. The disadvantages of conventional methods, based on the atom or ion stripping in a material target, are emittance growth, energy straggling, and production of ions in many charge states. Recently suggested stripping methods based on direct photoionization require employment of hard-UV lasers, which still do not exist and must obviously be very bulky and expensive. An alternative method, suggested for injection of proton beams, employs excitation of the atom to 3p intermediate state with subsequent Lorentz ionization in a magnetic field gradient. This technique applies rigid requirements to laser characteristic and is not free of growing of the beam divergence. In this paper a variant of the stripping technique based on the resonantly enhanced two-photon ionization (RETPI is considered. The technique allows ionization of singly charged ions of the elements from helium to bismuth. A variant of the technique can be used for proton injection. RETPI can be applied for both ion injection and stacking, as well as for diagnostics of ion beam characteristics on the orbit. Stripping efficiency can be about 100% for the singly charged ions having the singlet ground state and decreases for the other ions. Special methods for “cleaning” unwanted atomic states in such ions, that can provide high stripping efficiency, are discussed. Excimer lasers with very moderate parameters can be employed for implementation of this technique for almost all elements. Numerical examples show that for most of the singly charged ions and for hydrogen atom necessary laser-beam energy density is merely 0.5–8  J/cm^{2} for a 1 m interaction region, and is 10 times higher for several light ions.

Photoionization of the 4d subshell of the La isonuclear sequence

Science.gov (United States)

Kalyadan, Sindhu; Varma, Hari R.; Deshmukh, P. C.; Costello, J. T.; Hayden, P.; Manson, S. T.

2015-05-01

Photoionization studies along isonuclear sequences provide the required systematic data which are useful in many practical applications and also for testing the accuracy of various theoretical models. In the present work, we report on 4d subshell photoionization studies of some of the members of La (Z = 57) isonuclear sequence (La3+, La9+ and La11+) using relativistic random phase approximation (RRPA). Photoionization cross sections, σ, angular distribution asymmetry parameters, β, and the individual dipole matrix elements for 4d3/2 and 4d5/2 subshells are presented along with the 4d branching ratios of these ions. It is found that in La3+, the branching ratios show significant departure from the statistical value 1.5 due to the presence of Cooper minimum in the 4d --> f ionization channels. This departure is minor for the case of La9+ and La11+ since the Cooper minimum in these cases occur in the discrete part of the 4d spectrum.

Comparison of direct and alternating current vacuum ultraviolet lamps in atmospheric pressure photoionization.

Science.gov (United States)

Vaikkinen, Anu; Haapala, Markus; Kersten, Hendrik; Benter, Thorsten; Kostiainen, Risto; Kauppila, Tiina J

2012-02-07

A direct current induced vacuum ultraviolet (dc-VUV) krypton discharge lamp and an alternating current, radio frequency (rf) induced VUV lamp that are essentially similar to lamps in commercial atmospheric pressure photoionization (APPI) ion sources were compared. The emission distributions along the diameter of the lamp exit window were measured, and they showed that the beam of the rf lamp is much wider than that of the dc lamp. Thus, the rf lamp has larger efficient ionization area, and it also emits more photons than the dc lamp. The ionization efficiencies of the lamps were compared using identical spray geometries with both lamps in microchip APPI mass spectrometry (μAPPI-MS) and desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS). A comprehensive view on the ionization was gained by studying six different μAPPI solvent compositions, five DAPPI spray solvents, and completely solvent-free DAPPI. The observed reactant ions for each solvent composition were very similar with both lamps except for toluene, which showed a higher amount of solvent originating oxidation products with the rf lamp than with the dc lamp in μAPPI. Moreover, the same analyte ions were detected with both lamps, and thus, the ionization mechanisms with both lamps are similar. The rf lamp showed a higher ionization efficiency than the dc lamp in all experiments. The difference between the lamp ionization efficiencies was greatest when high ionization energy (IE) solvent compositions (IEs above 10 eV), i.e., hexane, methanol, and methanol/water, (1:1 v:v) were used. The higher ionization efficiency of the rf lamp is likely due to the larger area of high intensity light emission, and the resulting larger efficient ionization area and higher amount of photons emitted. These result in higher solvent reactant ion production, which in turn enables more efficient analyte ion production. © 2012 American Chemical Society

Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

Directory of Open Access Journals (Sweden)

Oleg A. Louchev

2016-09-01

Full Text Available We develop a set of analytical approximations for the estimation of the combined effect of various photoionization processes involved in the resonant four-wave mixing generation of ns pulsed Lyman-α (L-α radiation by using 212.556 nm and 820-845 nm laser radiation pulses in Kr-Ar mixture: (i multi-photon ionization, (ii step-wise (2+1-photon ionization via the resonant 2-photon excitation of Kr followed by 1-photon ionization and (iii laser-induced avalanche ionization produced by generated free electrons. Developed expressions validated by order of magnitude estimations and available experimental data allow us to identify the area for the operation under high input laser intensities avoiding the onset of full-scale discharge, loss of efficiency and inhibition of generated L-α radiation. Calculations made reveal an opportunity for scaling up the output energy of the experimentally generated pulsed L-α radiation without significant enhancement of photoionization.

Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

Science.gov (United States)

Louchev, Oleg A.; Saito, Norihito; Oishi, Yu; Miyazaki, Koji; Okamura, Kotaro; Nakamura, Jumpei; Iwasaki, Masahiko; Wada, Satoshi

2016-09-01

We develop a set of analytical approximations for the estimation of the combined effect of various photoionization processes involved in the resonant four-wave mixing generation of ns pulsed Lyman-α (L-α ) radiation by using 212.556 nm and 820-845 nm laser radiation pulses in Kr-Ar mixture: (i) multi-photon ionization, (ii) step-wise (2+1)-photon ionization via the resonant 2-photon excitation of Kr followed by 1-photon ionization and (iii) laser-induced avalanche ionization produced by generated free electrons. Developed expressions validated by order of magnitude estimations and available experimental data allow us to identify the area for the operation under high input laser intensities avoiding the onset of full-scale discharge, loss of efficiency and inhibition of generated L-α radiation. Calculations made reveal an opportunity for scaling up the output energy of the experimentally generated pulsed L-α radiation without significant enhancement of photoionization.

Experimental study of linear magnetic dichroism in photoionization satellite transitions of atomic rubidium

International Nuclear Information System (INIS)

Jaenkaelae, K.; Alagia, M.; Feyer, V.; Richter, R.; Prince, K. C.

2011-01-01

Laser orientation in the initial state has been used to study the properties of satellite transitions in inner-shell photoionization of rubidium atoms. The linear magnetic dichroism in the angular distribution (LMDAD) has been utilized to probe the continuum waves of orbital angular momentum conserving monopole, and angular momentum changing conjugate satellites, accompanying the 4p ionization of atomic Rb. We show experimentally that LMDAD of both types of satellite transitions is nonzero and that LMDAD of monopole satellites, measured as a function of photon energy, mimics the LMDAD of direct photoionization, whereas the LMDAD of conjugate transitions deviates drastically from that trend. The results indicate that conjugate transitions cannot be described theoretically without explicit inclusion of electron-electron interaction. The present data can thus be used as a very precise test of current models for photoionization.

VUV photoionization of acetamide studied by electron/ion coincidence spectroscopy in the 8-24 eV photon energy range

KAUST Repository

Schwell, Martin; Bé nilan, Yves; Fray, Nicolas; Gazeau, Marie Claire; Es-sebbar, Et-touhami; Garcí a, Gustavo A.; Nahon, Laurent; Champion, Norbert; Leach, Sydney Sydney

2012-01-01

A VUV photoionization study of acetamide was carried out over the 8-24 eV photon energy range using synchrotron radiation and photoelectron/photoion coincidence (PEPICO) spectroscopy. Threshold photoelectron photoion coincidence (TPEPICO) measurements were also made. Photoion yield curves and branching ratios were measured for the parent ion and six fragment ions. The adiabatic ionization energy of acetamide was determined as I.E. (1 2A′) = (9.71 ± 0.02) eV, in agreement with an earlier reported photoionization mass spectrometry (PIMS) value. The adiabatic energy of the first excited state of the ion, 1 2A″, was determined to be ≈10.1 eV. Assignments of the fragment ions and the pathways of their formation by dissociative photoionization were made. The neutral species lost in the principal dissociative photoionization processes are CH 3, NH 2, NH 3, CO, HCCO and NH 2CO. Heats of formation are derived for all ions detected and are compared with literature values. Some astrophysical implications of these results are discussed. © 2011 Elsevier B.V. All rights reserved.

Electric field vector measurements in a surface ionization wave discharge

International Nuclear Information System (INIS)

Goldberg, Benjamin M; Adamovich, Igor V; Lempert, Walter R; Böhm, Patrick S; Czarnetzki, Uwe

2015-01-01

This work presents the results of time-resolved electric field vector measurements in a short pulse duration (60 ns full width at half maximum), surface ionization wave discharge in hydrogen using a picosecond four-wave mixing technique. Electric field vector components are measured separately, using pump and Stokes beams linearly polarized in the horizontal and vertical planes, and a polarizer placed in front of the infrared detector. The time-resolved electric field vector is measured at three different locations across the discharge gap, and for three different heights above the alumina ceramic dielectric surface, ∼100, 600, and 1100 μm (total of nine different locations). The results show that after breakdown, the discharge develops as an ionization wave propagating along the dielectric surface at an average speed of 1 mm ns −1 . The surface ionization wave forms near the high voltage electrode, close to the dielectric surface (∼100 μm). The wave front is characterized by significant overshoot of both vertical and horizontal electric field vector components. Behind the wave front, the vertical field component is rapidly reduced. As the wave propagates along the dielectric surface, it also extends further away from the dielectric surface, up to ∼1 mm near the grounded electrode. The horizontal field component behind the wave front remains quite significant, to sustain the electron current toward the high voltage electrode. After the wave reaches the grounded electrode, the horizontal field component experiences a secondary rise in the quasi-dc discharge, where it sustains the current along the near-surface plasma sheet. The measurement results indicate presence of a cathode layer formed near the grounded electrode with significant cathode voltage fall, ≈3 kV, due to high current density in the discharge. The peak reduced electric field in the surface ionization wave is 85–95 Td, consistent with dc breakdown field estimated from the Paschen

Photoionization of Endohedral Atoms: Collective, Reflective and Collateral Emissions

International Nuclear Information System (INIS)

Chakraborty, Himadri S.; McCune, Matthew A.; Hopper, Dale E.; Madjet, Mohamed E.; Manson, Steven T.

2009-01-01

The photoionization properties of a fullerene-confined atom differ dramatically from that of an isolated atom. In the low energy region, where the fullerene plasmons are active, the electrons of the confined atom emerge through a collective channel carrying a significant chunk of plasmon with it. The photoelectron angular distribution of the confined atom however shows far lesser impact of the effect. At higher energies, the interference between two single-electron ionization channels, one directly from the atom and another reflected off the fullerene cage, producuces oscillatory cross sections. But for the outermost atomic level, which transfers some electrons to the cage, oscillations are further modulated by the collateral emission from the part of the atomic charge density transferred to the cage. These various modes of emissions are studied for the photoionization of Ar endohedrally confined in C 60 .

Dissociative Photoionization of 1-Halogenated Silacyclohexanes: Silicon Traps the Halogen.

Science.gov (United States)

Bodi, Andras; Sigurdardottir, Katrin Lilja; Kvaran, Ágúst; Bjornsson, Ragnar; Arnason, Ingvar

2016-11-23

The threshold photoelectron spectra and threshold photoionization mass spectra of 1-halogenated-1-silacyclohexanes, for the halogens X = F, Cl, Br, and I, have been obtained using synchrotron vacuum ultraviolet radiation and photoelectron photoion coincidence spectroscopy. As confirmed by a similar ionization onset and density functional theory molecular orbitals, the ionization to the ground state is dominated by electron removal from the silacyclohexane ring for X = F, Cl, and Br, and from the halogen lone pair for X = I. The breakdown diagrams show that the dissociative photoionization mechanism is also different for X = I. Whereas the parent ions decay by ethylene loss for X = F to Br in the low-energy regime, the iodine atom is lost for X = I. The first step is followed by a sequential ethylene loss at higher internal energies in each of the compounds. It is argued that the tendency of silicon to lower bond angles stabilizes the complex cation in which C 2 H 4 is η 2 -coordinated to it, and which precedes ethylene loss. Together with the relatively strong silicon-halogen bonds and the increased inductive effect of the silacyclohexane ring in stabilizing the cation, this explains the main differences observed in the fragmentation of the halogenated silacyclohexane and halogenated cyclohexane ions. The breakdown diagrams have been modeled taking into account slow dissociations at threshold and the resulting kinetic shift. The 0 K appearance energies have been obtained to within 0.08 eV for the ethylene loss for X = F to Br (10.56, 10.51, and 10.51 eV, respectively), the iodine atom loss for X = I (10.11 eV), the sequential ethylene loss for X = F to I (12.29, 12.01, 11.94, and 11.86 eV, respectively), and the minor channels of H loss for X = F (10.56 eV) and propylene loss in X = Cl (also at 10.56 eV). The appearance energies for the major channels likely correspond to the dissociative photoionization reaction energy.

Photoionization sensor CES for non-invasive medical diagnostics

Science.gov (United States)

Mustafaev, Aleksandr; Rastvorova, Iuliia; Khobnya, Kristina; Podenko, Sofia

2016-10-01

Method CES (collisional electron spectroscopy), patented in Russia, the USA, Japan, China, Germany and Britain, allows to analyze the gaseous mixtures using electron spectroscopy under high pressures up to atmospheric without using vacuum. The design of VUV photoionization detector was developed based on this method. Such detector is used as a portable gas analyzer for continuous personal bio-medical monitoring. This detector measures energy of electrons produced in ionization with resonance photons, whose wavelength situated in the vacuum ultraviolet (VUV). Nowadays, micro plasma source of such photons on resonant line of Kr with energy of 10,6 eV is developed. Only impurities are ionized and detected by the VUV-emission, meanwhile the main components of air stay neutral that reduces background signal and increases the sensibility along with accuracy. The experimental facilities with VUV photoionization sensors CES are constructed with the overall sizes about 10*10*1 mm. The watt consumption may comprise less than 1W. Increase of electrometer amplifier's sensibility and more high-aperture construction are used today to increase the sensibility of CES-detectors. The wide range of detectable molecules and high sensitivity allow the development of portable device, which can become the base of the future preventive medicine. Work supported by Foundation for Assistance to Small Innovative Enterprises in Science and Technology.

Photoionization of resonantly driven atomic states by an extreme ultraviolet-free-electron laser: intensity dependence and renormalization of Rabi frequencies

International Nuclear Information System (INIS)

Kaiser, B; Brand, A; Glässl, M; Vagov, A; Axt, V M; Pietsch, U

2013-01-01

We analyze theoretically the high intensity photoionization dynamics of a system with two atomic states resonantly coupled by coherent extreme ultraviolet laser radiation that also gives rise to the ionization. The ground state occupation of such a system is shown to exhibit damped Rabi oscillations. The corresponding ionization, which is responsible for the damping, scales almost linearly with the field intensity when the pulse length exceeds the Rabi period. For shorter pulses a quadratic scaling is found. The Rabi frequency is shifted compared to its value for an isolated two-level system. The shift increases with excitation intensity and can acquire a high percentage of the unrenormalized frequency at high intensities. Analytical results obtained within a simplified solvable model demonstrate that the damping and the shift both result from the coupling of the discrete states to the ionization continuum and are therefore closely related. Numerical simulations for a two-electron system reveal at high intensities the importance of off-resonant ionization channels. (paper)

Ionization probes of molecular structure and chemistry

Energy Technology Data Exchange (ETDEWEB)

Johnson, P.M. [State Univ. of New York, Stony Brook (United States)

1993-12-01

Various photoionization processes provide very sensitive probes for the detection and understanding of the spectra of molecules relevant to combustion processes. The detection of ionization can be selective by using resonant multiphoton ionization or by exploiting the fact that different molecules have different sets of ionization potentials. Therefore, the structure and dynamics of individual molecules can be studied even in a mixed sample. The authors are continuing to develop methods for the selective spectroscopic detection of molecules by ionization, and to use these methods for the study of some molecules of combustion interest.

Internuclear Separation Dependent Ionization of the Valence Orbitals of I2 by Strong Laser Fields

Science.gov (United States)

Chen, H.; Tagliamonti, V.; Gibson, G. N.

2012-11-01

Using a pump-dump-probe technique and Fourier-transform spectroscopy, we study the internuclear separation R dependence and relative strength of the ionization rates of the π and σ electrons of I2, whose valence orbitals are σg2πu4πg4σu0. We find that ionization of the highest occupied molecular orbital (HOMO)-2 (σg) has a strong dependence on R while the HOMO and HOMO-1 do not. Surprisingly, the ionization rate of the HOMO-2 exceeds the combined ionization rate of the less bound orbitals and this branching ratio increases with R. Since our technique produces target molecules that are highly aligned with the laser polarization, the σ orbitals will be preferentially ionized and undergo enhanced ionization at larger R compared to the π orbitals. Nevertheless, it is highly unusual that an inner orbital provides the dominant strong field ionization pathway in a small molecule.

Photoionization of radiation-induced traps in quartz and alkali feldspars.

Science.gov (United States)

Hütt, G; Jaek, I; Vasilchenko, V

2001-01-01

For the optimization of luminescence dating and dosimetry techniques on the basis of the optically stimulated luminescence, the stimulation spectra of quartz and alkali feldspars were measured in the spectral region of 250-1100 nm using optically stimulated afterglow. Optically stimulated luminescence in all studied spectral regions is induced by the same kind of deep traps, that produce thermoluminescence in the regions of palaeodosimetric peaks for both minerals. The mechanism for photoionization of deep traps was proposed as being due to delocalization of the excited state of the corresponding lattice defects. The excited state overlaps the zone states; i.e. is situated in the conduction band. Because of the high quantum yield of deep electron trap ionization in the UV spectral region, the present aim was to study the possibility of using UV-stimulation for palaeodose reconstruction.

Photoionization of radiation-induced traps in quartz and alkali feldspars

International Nuclear Information System (INIS)

Huett, G.; Jaek, I.; Vasilchenko, V.

2001-01-01

For the optimization of luminescence dating and dosimetry techniques on the basis of the optically stimulated luminescence, the stimulation spectra of quartz and alkali feldspars were measured in the spectral region of 250-1100 nm using optically stimulated afterglow. Optically stimulated luminescence in all studied spectral regions is induced by the same kind of deep traps, that produce thermoluminescence in the regions of palaeodosimetric peaks for both minerals. The mechanism for photoionization of deep traps was proposed as being due to delocalization of the excited state of the corresponding lattice defects. The excited state overlaps the zone states; i.e. is situated in the conduction band. Because of the high quantum yield of deep electron trap ionization in the UV spectral region, the present aim was to study the possibility of using UV-stimulation for palaeodose reconstruction

Photoionization of radiation-induced traps in quartz and alkali feldspars

Energy Technology Data Exchange (ETDEWEB)

Huett, G. E-mail: hutt@pdos.gi.ee; Jaek, I.; Vasilchenko, V

2001-01-15

For the optimization of luminescence dating and dosimetry techniques on the basis of the optically stimulated luminescence, the stimulation spectra of quartz and alkali feldspars were measured in the spectral region of 250-1100 nm using optically stimulated afterglow. Optically stimulated luminescence in all studied spectral regions is induced by the same kind of deep traps, that produce thermoluminescence in the regions of palaeodosimetric peaks for both minerals. The mechanism for photoionization of deep traps was proposed as being due to delocalization of the excited state of the corresponding lattice defects. The excited state overlaps the zone states; i.e. is situated in the conduction band. Because of the high quantum yield of deep electron trap ionization in the UV spectral region, the present aim was to study the possibility of using UV-stimulation for palaeodose reconstruction.

Development of a hand-portable photoionization time-of-flight mass spectrometer

International Nuclear Information System (INIS)

Dieckman, S.L.; Bostrom, G.A.; Waterfield, L.G.; Jendrzejczyk, J.A.; Raptis, A.C.

1996-01-01

ANL is currently developing a portable chemical sensor system based on laser desorption photoionization time-of-flight mass spectrometry. It will incorporate direct sampling, a cryocooler base sample adsorption and concentration, and direct surface multiphoton ionization. All components will be in a package 9 x 11 x 4 in., weighing 15-18 lbs. A sample spectrum is given for a NaCl sample

Spectroscopy of X-ray Photoionized Plasmas in the Laboratory

Science.gov (United States)

Liedahl, Duane A.; Loisel, Guillaume; Bailey, James E.; Nagayama, Taisuke; Hansen, Stephanie B.; Rochau, Gregory; Fontes, Christopher J.; Mancini, Roberto; Kallman, Timothy R.

2018-06-01

The physical processes operating in astrophysical plasmas --- heating, cooling, ionization, recombination, level population kinetics, and radiation transport --- are all accessible to observation in the laboratory. What distinguishes X-ray photoionized plasmas from the more common case of high-temperature collisionally-ionized plasmas is the elevated level of importance of the radiation/matter interaction. The advent of laboratory facilities with the capability to generate high-powered X-ray sources has provided the means by which to study this interaction, which is also fundamental to active galactic nuclei and other accretion-powered objects. We discuss recent and ongoing experiments, with an emphasis on X-ray spectroscopic measurements of silicon plasmas obtained at the Sandia Z Pulsed Power Facility.

Photoionization of Co+ and electron-impact excitation of Co2 + using the Dirac R-matrix method

Science.gov (United States)

Tyndall, N. B.; Ramsbottom, C. A.; Ballance, C. P.; Hibbert, A.

2016-11-01

Modelling of massive stars and supernovae (SNe) plays a crucial role in understanding galaxies. From this modelling we can derive fundamental constraints on stellar evolution, mass-loss processes, mixing, and the products of nucleosynthesis. Proper account must be taken of all important processes that populate and depopulate the levels (collisional excitation, de-excitation, ionization, recombination, photoionization, bound-bound processes). For the analysis of Type Ia SNe and core collapse SNe (Types Ib, Ic and II) Fe group elements are particularly important. Unfortunately little data is currently available and most noticeably absent are the photoionization cross-sections for the Fe-peaks which have high abundances in SNe. Important interactions for both photoionization and electron-impact excitation are calculated using the relativistic Dirac atomic R-matrix codes (DARC) for low-ionization stages of Cobalt. All results are calculated up to photon energies of 45 eV and electron energies up to 20 eV. The wavefunction representation of Co III has been generated using GRASP0 by including the dominant 3d7, 3d6[4s, 4p], 3p43d9 and 3p63d9 configurations, resulting in 292 fine structure levels. Electron-impact collision strengths and Maxwellian averaged effective collision strengths across a wide range of astrophysically relevant temperatures are computed for Co III. In addition, statistically weighted level-resolved ground and metastable photoionization cross-sections are presented for Co II and compared directly with existing work.

Photoionization modeling of the LWS fine-structure lines in IR bright galaxies

Science.gov (United States)

Satyapal, S.; Luhman, M. L.; Fischer, J.; Greenhouse, M. A.; Wolfire, M. G.

1997-01-01

The long wavelength spectrometer (LWS) fine structure line spectra from infrared luminous galaxies were modeled using stellar evolutionary synthesis models combined with photoionization and photodissociation region models. The calculations were carried out by using the computational code CLOUDY. Starburst and active galactic nuclei models are presented. The effects of dust in the ionized region are examined.

Photoionization and photofragmentation of multiply charged Lu3N@C80 ions

International Nuclear Information System (INIS)

Hellhund, J; Borovik, A Jr; Holste, K; Ricz, S; Schippers, S; Müller, A; Klumpp, S; Martins, M

2015-01-01

Relative cross sections for photoionization and photofragmentation of endohedral fullerene Lu 3 N@C 80 q+ (q=1,2,3) ions have been measured employing the new photon-ion spectrometer PIPE at PETRA III. Prominent structures related to the carbon K-shell ionization threshold were observed in the energy range 280 to 330 eV. (paper)

Desorption atmospheric pressure photoionization high-resolution mass spectrometry: a complementary approach for the chemical analysis of atmospheric aerosols.

Science.gov (United States)

Parshintsev, Jevgeni; Vaikkinen, Anu; Lipponen, Katriina; Vrkoslav, Vladimir; Cvačka, Josef; Kostiainen, Risto; Kotiaho, Tapio; Hartonen, Kari; Riekkola, Marja-Liisa; Kauppila, Tiina J

2015-07-15

On-line chemical characterization methods of atmospheric aerosols are essential to increase our understanding of physicochemical processes in the atmosphere, and to study biosphere-atmosphere interactions. Several techniques, including aerosol mass spectrometry, are nowadays available, but they all suffer from some disadvantages. In this research, desorption atmospheric pressure photoionization high-resolution (Orbitrap) mass spectrometry (DAPPI-HRMS) is introduced as a complementary technique for the fast analysis of aerosol chemical composition without the need for sample preparation. Atmospheric aerosols from city air were collected on a filter, desorbed in a DAPPI source with a hot stream of toluene and nitrogen, and ionized using a vacuum ultraviolet lamp at atmospheric pressure. To study the applicability of the technique for ambient aerosol analysis, several samples were collected onto filters and analyzed, with the focus being on selected organic acids. To compare the DAPPI-HRMS data with results obtained by an established method, each filter sample was divided into two equal parts, and the second half of the filter was extracted and analyzed by liquid chromatography/mass spectrometry (LC/MS). The DAPPI results agreed with the measured aerosol particle number. In addition to the targeted acids, the LC/MS and DAPPI-HRMS methods were found to detect different compounds, thus providing complementary information about the aerosol samples. DAPPI-HRMS showed several important oxidation products of terpenes, and numerous compounds were tentatively identified. Thanks to the soft ionization, high mass resolution, fast analysis, simplicity and on-line applicability, the proposed methodology has high potential in the field of atmospheric research. Copyright © 2015 John Wiley & Sons, Ltd.

Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

OpenAIRE

Oleg A. Louchev; Norihito Saito; Yu Oishi; Koji Miyazaki; Kotaro Okamura; Jumpei Nakamura; Masahiko Iwasaki; Satoshi Wada

2016-01-01

We develop a set of analytical approximations for the estimation of the combined effect of various photoionization processes involved in the resonant four-wave mixing generation of ns pulsed Lyman-α (L-α) radiation by using 212.556 nm and 820-845 nm laser radiation pulses in Kr-Ar mixture: (i) multi-photon ionization, (ii) step-wise (2+1)-photon ionization via the resonant 2-photon excitation of Kr followed by 1-photon ionization and (iii) laser-induced avalanche ionization produced by genera...

Automatic system for evaluation of ionizing field

International Nuclear Information System (INIS)

Pimenta, N.L.; Calil, S.J.

1992-01-01

A three-dimensional cartesian manipulator for evaluating the ionizing field and able to position a ionization chamber in any point of the space is developed. The control system is made using a IBM microcomputer. The system aimed the study of isodose curves from ionizing sources, verifying the performance of radiotherapeutic equipment. (C.G.C.)

Effects of relativistic small radial component on atomic photoionization cross sections

International Nuclear Information System (INIS)

Liu Xiaobin; Xing Yongzhong; Sun Xiaowei

2008-01-01

The effects of relativistic small radial component on atomic photoionization cross sections have been studied within relativistic average self-consistent field theory. Relativistic effects are relatively unimportant for low photon energy, along with a review of high-energy photoionization the relativistic effects are quite important. The effects of relativistic small radial component on photoionization process should show breakdown when the nuclear finite-size effects is taken into account. The compression of wavefunction into the space near nucleus is so strong in highly charged ions that the electronic radius greatly decreases, and the effects of relativistic small radial component on photoionization cross sections turn to stronger than ordinary atoms. Since relativistic effects are extremely sensitive to the behavior of small radial component, the results are in good agreement with relativistic effects on photoionization cross section. (authors)

On the SIMS Ionization Probability of Organic Molecules.

Science.gov (United States)

Popczun, Nicholas J; Breuer, Lars; Wucher, Andreas; Winograd, Nicholas

2017-06-01

The prospect of improved secondary ion yields for secondary ion mass spectrometry (SIMS) experiments drives innovation of new primary ion sources, instrumentation, and post-ionization techniques. The largest factor affecting secondary ion efficiency is believed to be the poor ionization probability (α + ) of sputtered material, a value rarely measured directly, but estimated to be in some cases as low as 10 -5 . Our lab has developed a method for the direct determination of α + in a SIMS experiment using laser post-ionization (LPI) to detect neutral molecular species in the sputtered plume for an organic compound. Here, we apply this method to coronene (C 24 H 12 ), a polyaromatic hydrocarbon that exhibits strong molecular signal during gas-phase photoionization. A two-dimensional spatial distribution of sputtered neutral molecules is measured and presented. It is shown that the ionization probability of molecular coronene desorbed from a clean film under bombardment with 40 keV C 60 cluster projectiles is of the order of 10 -3 , with some remaining uncertainty arising from laser-induced fragmentation and possible differences in the emission velocity distributions of neutral and ionized molecules. In general, this work establishes a method to estimate the ionization efficiency of molecular species sputtered during a single bombardment event. Graphical Abstract GRAPHICAL ABSTRACT TEXT HERE] -->.

Beyond Naphthenic Acids: Environmental Screening of Water from Natural Sources and the Athabasca Oil Sands Industry Using Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Science.gov (United States)

Barrow, Mark P; Peru, Kerry M; Fahlman, Brian; Hewitt, L Mark; Frank, Richard A; Headley, John V

2015-09-01

There is a growing need for environmental screening of natural waters in the Athabasca region of Alberta, Canada, particularly in the differentiation between anthropogenic and naturally-derived organic compounds associated with weathered bitumen deposits. Previous research has focused primarily upon characterization of naphthenic acids in water samples by negative-ion electrospray ionization methods. Atmospheric pressure photoionization is a much less widely used ionization method, but one that affords the possibility of observing low polarity compounds that cannot be readily observed by electrospray ionization. This study describes the first usage of atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (in both positive-ion and negative-ion modes) to characterize and compare extracts of oil sands process water, river water, and groundwater samples from areas associated with oil sands mining activities. When comparing mass spectra previously obtained by electrospray ionization and data acquired by atmospheric pressure photoionization, there can be a doubling of the number of components detected. In addition to polar compounds that have previously been observed, low-polarity, sulfur-containing compounds and hydrocarbons that do not incorporate a heteroatom were detected. These latter components, which are not amenable to electrospray ionization, have potential for screening efforts within monitoring programs of the oil sands.

Femtosecond photoionization of atoms under noise

International Nuclear Information System (INIS)

Singh, Kamal P.; Rost, Jan M.

2007-01-01

We investigate the effect of incoherent perturbations on atomic photoionization due to a femtosecond midinfrared laser pulse by solving the time-dependent stochastic Schroedinger equation. For a weak laser pulse which causes almost no ionization, an addition of a Gaussian white noise to the pulse leads to a significantly enhanced ionization probability. Tuning the noise level, a stochastic resonancelike curve is observed showing the existence of an optimum noise for a given laser pulse. Besides studying the sensitivity of the obtained enhancement curve on the pulse parameters, such as the pulse duration and peak amplitude, we suggest that experimentally realizable broadband chaotic light can also be used instead of the white noise to observe similar features. The underlying enhancement mechanism is analyzed in the frequency domain by computing a frequency-resolved atomic gain profile, as well as in the time domain by controlling the relative delay between the action of the laser pulse and noise

Interferometric analysis of laboratory photoionized plasmas utilizing supersonic gas jet targets.

Science.gov (United States)

Swanson, Kyle James; Ivanov, Vladimir; Mancini, Roberto; Mayes, Daniel C.

2018-06-01

Photoionized plasmas are an important component of active galactic nuclei, x-ray binary systems and other astrophysical objects. Laboratory produced photoionized plasmas have mainly been studied at large scale facilities, due to the need for high intensity broadband x-ray flux. Using supersonic gas jets as targets has allowed university scale pulsed power generators to begin similar research. The two main advantages of this approach with supersonic gas jets include: possibility of a closer location to the x-ray source and no attenuation related to material used for containment and or tamping. Due to these factors, this experimental platform creates a laboratory environment that more closely resembles astrophysical environments. This system was developed at the Nevada Terawatt Facility using the 1 MA pulsed power generator Zebra. Neon, argon, and nitrogen supersonic gas jets are produced approximately 7-8mm from the z-pinch axis. The high intensity broadband x-ray flux produced by the collapse of the z-pinch wire array implosion irradiates the gas jet. Cylindrical wire arrays are made with 4 and 8 gold 10µm thick wire. The z-pinch radiates approximately 12-16kj of x-ray energy, with x-ray photons under 1Kev in energy. The photoionized plasma is measured via x-ray absorption spectroscopy and interferometry. A Mach-Zehnder interferometer is used to the measure neutral density of the jet prior to the zebra shot at a wavelength of 266 nm. A dual channel air-wedge shearing interferometer is used to measure electron density of the ionized gas jet during the shot, at wavelengths of 532nm and 266nm. Using a newly developed interferometric analysis tool, average ionization state maps of the plasma can be calculated. Interferometry for nitrogen and argon show an average ionization state in the range of 3-8. Preliminary x-ray absorption spectroscopy collected show neon absorption lines. This work was sponsored in part by DOE Office of Science Grant DE-SC0014451.

IZI: INFERRING THE GAS PHASE METALLICITY (Z) AND IONIZATION PARAMETER (q) OF IONIZED NEBULAE USING BAYESIAN STATISTICS

Energy Technology Data Exchange (ETDEWEB)

Blanc, Guillermo A. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Kewley, Lisa; Vogt, Frédéric P. A.; Dopita, Michael A. [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611 (Australia)

2015-01-10

We present a new method for inferring the metallicity (Z) and ionization parameter (q) of H II regions and star-forming galaxies using strong nebular emission lines (SELs). We use Bayesian inference to derive the joint and marginalized posterior probability density functions for Z and q given a set of observed line fluxes and an input photoionization model. Our approach allows the use of arbitrary sets of SELs and the inclusion of flux upper limits. The method provides a self-consistent way of determining the physical conditions of ionized nebulae that is not tied to the arbitrary choice of a particular SEL diagnostic and uses all the available information. Unlike theoretically calibrated SEL diagnostics, the method is flexible and not tied to a particular photoionization model. We describe our algorithm, validate it against other methods, and present a tool that implements it called IZI. Using a sample of nearby extragalactic H II regions, we assess the performance of commonly used SEL abundance diagnostics. We also use a sample of 22 local H II regions having both direct and recombination line (RL) oxygen abundance measurements in the literature to study discrepancies in the abundance scale between different methods. We find that oxygen abundances derived through Bayesian inference using currently available photoionization models in the literature can be in good (∼30%) agreement with RL abundances, although some models perform significantly better than others. We also confirm that abundances measured using the direct method are typically ∼0.2 dex lower than both RL and photoionization-model-based abundances.

IZI: INFERRING THE GAS PHASE METALLICITY (Z) AND IONIZATION PARAMETER (q) OF IONIZED NEBULAE USING BAYESIAN STATISTICS

International Nuclear Information System (INIS)

Blanc, Guillermo A.; Kewley, Lisa; Vogt, Frédéric P. A.; Dopita, Michael A.

2015-01-01

We present a new method for inferring the metallicity (Z) and ionization parameter (q) of H II regions and star-forming galaxies using strong nebular emission lines (SELs). We use Bayesian inference to derive the joint and marginalized posterior probability density functions for Z and q given a set of observed line fluxes and an input photoionization model. Our approach allows the use of arbitrary sets of SELs and the inclusion of flux upper limits. The method provides a self-consistent way of determining the physical conditions of ionized nebulae that is not tied to the arbitrary choice of a particular SEL diagnostic and uses all the available information. Unlike theoretically calibrated SEL diagnostics, the method is flexible and not tied to a particular photoionization model. We describe our algorithm, validate it against other methods, and present a tool that implements it called IZI. Using a sample of nearby extragalactic H II regions, we assess the performance of commonly used SEL abundance diagnostics. We also use a sample of 22 local H II regions having both direct and recombination line (RL) oxygen abundance measurements in the literature to study discrepancies in the abundance scale between different methods. We find that oxygen abundances derived through Bayesian inference using currently available photoionization models in the literature can be in good (∼30%) agreement with RL abundances, although some models perform significantly better than others. We also confirm that abundances measured using the direct method are typically ∼0.2 dex lower than both RL and photoionization-model-based abundances

Online characterization of isomeric/isobaric components in the gas phase of mainstream cigarette smoke by tunable synchrotron radiation vacuum ultraviolet photoionization time-of-flight mass spectrometry and photoionization efficiency curve simulation.

Science.gov (United States)

Pan, Yang; Hu, Yonghua; Wang, Jian; Ye, Lili; Liu, Chengyuan; Zhu, Zhixiang

2013-12-17

A newly developed, qualitative and quantitative method based on tunable synchrotron radiation vacuum ultraviolet photoionization time-of-flight mass spectrometry (SR-VUV-PI-TOFMS) and photoionization efficiency (PIE) curve simulation was applied for the online analysis of isomers and isobaric compounds in the gas phase of mainstream cigarette smoke. After blocking the particulate phase components by the Cambridge filter pad, a puff of fresh gas-phase cigarette smoke was immediately introduced into a vacuum ionization chamber through a heated capillary, then was photoionized, and analyzed by a TOF mass spectrometer. The PIE curves for the mass peaks up to m/z = 106 were measured between 8.0 and 10.7 eV. Some components could be directly identified by their discriminated ionization energies (IEs) on the PIE curve. By simulating the PIE curve with the sum of scaled absolute photoionization cross sections (PICSs), complex isomeric/isobaric compounds along with their mole fractions could be obtained when the best-fitting was realized between experimental and simulated PIE curves. A series of reported toxic compounds for quantification, such as 1,3-butadiene (m/z = 54), 1,3-cyclopentadiene (m/z = 66), benzene (m/z = 78), xylene (m/z = 106), 2-propenal (m/z = 56), acetone and propanal (m/z = 58), crotonaldehyde (m/z = 70), furan and isoprene (m/z = 68), were all found to have other isomers and/or isobaric compounds with considerable abundances. Some isomers have never been reported previously in cigarette smoke, like C5H6 isomers 1-penten-3-yne, 3-penten-1-yne, and 1-penten-4-yne at m/z = 66. Isomeric/isobaric compounds characterization for the mass peaks and mole fraction calculations were discussed in detail below 10.7 eV, an energy value covering several conventional used VUV light sources.

Ionization of xenon by electrons: Partial cross sections for single, double, and triple ionization

International Nuclear Information System (INIS)

Mathur, D.; Badrinathan, C.

1987-01-01

High-sensitivity measurements of relative partial cross sections for single, double, and triple ionization of Xe by electron impact have been carried out in the energy region from threshold to 100 eV using a crossed-beam apparatus incorporating a quadrupole mass spectrometer. The weighted sum of the relative partial cross sections at 50 eV are normalized to the total ionization cross section of Rapp and Englander-Golden to yield absolute cross-section functions. Shapes of the partial cross sections for single and double ionization are difficult to account for within a single-particle picture. Comparison of the Xe + data with 4d partial photoionization cross-section measurements indicates the important role played by many-body effects in describing electron-impact ionization of high-Z atoms

High-frequency two-electron photoionization cross section of triplet states

International Nuclear Information System (INIS)

Krivec, R.; Amusia, M.Ya.; Mandelzweig, V.B.

2003-01-01

Using high precision wave functions describing the triplet ground and excited 3 S states of the He atom and heliumlike ions, the cross sections of single- and double-electron photoionization are calculated. The dependence of the ratio R of the double and single ionization cross sections on the nuclear charge Z and the principal quantum number of excitation n is studied. The results obtained are compared to those for previously studied singlet states

Impact of local electrostatic field rearrangement on field ionization

Science.gov (United States)

Katnagallu, Shyam; Dagan, Michal; Parviainen, Stefan; Nematollahi, Ali; Grabowski, Blazej; Bagot, Paul A. J.; Rolland, Nicolas; Neugebauer, Jörg; Raabe, Dierk; Vurpillot, François; Moody, Michael P.; Gault, Baptiste

2018-03-01

Field ion microscopy allows for direct imaging of surfaces with true atomic resolution. The high charge density distribution on the surface generates an intense electric field that can induce ionization of gas atoms. We investigate the dynamic nature of the charge and the consequent electrostatic field redistribution following the departure of atoms initially constituting the surface in the form of an ion, a process known as field evaporation. We report on a new algorithm for image processing and tracking of individual atoms on the specimen surface enabling quantitative assessment of shifts in the imaged atomic positions. By combining experimental investigations with molecular dynamics simulations, which include the full electric charge, we confirm that change is directly associated with the rearrangement of the electrostatic field that modifies the imaging gas ionization zone. We derive important considerations for future developments of data reconstruction in 3D field ion microscopy, in particular for precise quantification of lattice strains and characterization of crystalline defects at the atomic scale.

Synthetic oligomer analysis using atmospheric pressure photoionization mass spectrometry at different photon energies.

Science.gov (United States)

Desmazières, Bernard; Legros, Véronique; Giuliani, Alexandre; Buchmann, William

2014-01-15

Atmospheric pressure photoionization (APPI) followed by mass spectrometric detection was used to ionize a variety of polymers: polyethylene glycol, polymethyl methacrylate, polystyrene, and polysiloxane. In most cases, whatever the polymer or the solvent used (dichloromethane, tetrahydrofuran, hexane, acetone or toluene), only negative ion mode produced intact ions such as chlorinated adducts, with no or few fragmentations, in contrast to the positive ion mode that frequently led to important in-source fragmentations. In addition, it was shown that optimal detection of polymer distributions require a fine tuning of other source parameters such as temperature and ion transfer voltage. Series of mass spectra were recorded in the negative mode, in various solvents (dichloromethane, tetrahydrofuran, hexane, toluene, and acetone), by varying the photon energy from 8eV up to 10.6eV using synchrotron radiation. To these solvents, addition of a classical APPI dopant (toluene or acetone) was not necessary. Courtesy of the synchrotron radiation, it was demonstrated that the photon energy required for an efficient ionization of the polymer was correlated to the ionization energy of the solvent. As commercial APPI sources typically use krypton lamps with energy fixed at 10eV and 10.6eV, the study of the ionization of polymers over a wavelength range allowed to confirm and refine the previously proposed ionization mechanisms. Moreover, the APPI source can efficiently be used as an interface between size exclusion chromatography or reverse phase liquid chromatography and MS for the study of synthetic oligomers. However, the photoionization at fixed wavelength of polymer standards with different molecular weights showed that it was difficult to obtain intact ionized oligomers with molecular weights above a few thousands. Copyright © 2013 Elsevier B.V. All rights reserved.

Techniques for the generation and monitoring of vapors

International Nuclear Information System (INIS)

Nelson, G.O.

1981-01-01

Controlled test atmospheres can be produced using a variety of techniques. Gases are usually generated by using flow dilution methods while vapors are produced by using solvent injection and vaporization, saturation, permeation and diffusion techniques. The resulting gas mixtures can be monitored and measured using flame ionization, photoionization, electrochemical and infrared analytical systems. An ideal system for the production of controlled test atmospheres would not only be able to generate controlled test atmospheres, but also monitor all pertinent environmental parameters, such as temperature, humidity, and air flow

Probing photoelectron multiple interferences via Fourier spectroscopy in energetic photoionization of Xe-C60

International Nuclear Information System (INIS)

Potter, Andrea; McCune, Matthew A.; De, Ruma; Chakraborty, Himadri S.; Madjet, Mohamed E.

2010-01-01

Considering the photoionization of the Xe-C 60 endohedral compound, we study in detail the ionization cross sections of various levels of the system at energies higher than the plasmon resonance region. Five classes of single-electron levels are identified depending on their spectral character. Each class engenders distinct oscillations in the cross section, emerging from the interference between active ionization modes specific to that class. Analysis of the cross sections based on their Fourier transforms unravels oscillation frequencies that carry unique fingerprints of the emitting level.

Photoionization of Ne8+

Science.gov (United States)

Pindzola, M. S.; Abdel-Naby, Sh. A.; Robicheaux, F.; Colgan, J.

2014-05-01

Single and double photoionization cross sections for Ne8+ are calculated using a non-perturbative fully relativistic time-dependent close-coupling method. A Bessel function expansion is used to include both dipole and quadrupole effects in the radiation field interaction and the repulsive interaction between electrons includes both the Coulomb and Gaunt interactions. The fully correlated ground state of Ne8+ is obtained by solving a time-independent inhomogeneous set of close-coupled equations. Propagation of the time-dependent close-coupled equations yields single and double photoionization cross sections for Ne8+ at energies easily accessible at advanced free electron laser facilities. This work was supported in part by grants from NSF and US DoE. Computational work was carried out at NERSC in Oakland, California, NICS in Knoxville, Tennessee, and OLCF in Oak Ridge, Tennessee.

Excitation energies, photoionization cross sections, and asymmetry parameters of the methyl and silyl radicals.

Science.gov (United States)

Velasco, A M; Lavín, C; Dolgounitcheva, O; Ortiz, J V

2014-08-21

Vertical excitation energies of the methyl and silyl radicals were inferred from ab initio electron propagator calculations on the electron affinities of CH3(+) and SiH3(+). Photoionization cross sections and angular distribution of photoelectrons for the outermost orbitals of both CH3 and SiH3 radicals have been obtained with the Molecular Quantum Defect Orbital method. The individual ionization cross sections corresponding to the Rydberg channels to which the excitation of the ground state's outermost electron gives rise are reported. Despite the relevance of methyl radical in atmospheric chemistry and combustion processes, only data for the photon energy range of 10-11 eV seem to be available. Good agreement has been found with experiment for photoionization cross section of this radical. To our knowledge, predictions of the above mentioned photoionization parameters on silyl radical are made here for the first time, and we are not aware of any reported experimental measurements. An analysis of our results reveals the presence of a Cooper minimum in the photoionization of the silyl radical. The adequacy of the two theoretical procedures employed in the present work is discussed.

High-Resolution Photoionization, Photoelectron and Photodissociation Studies. Determination of Accurate Energetic and Spectroscopic Database for Combustion Radicals and Molecules

Energy Technology Data Exchange (ETDEWEB)

Ng, Cheuk-Yiu [Univ. of California, Davis, CA (United States)

2016-04-25

The main goal of this research program was to obtain accurate thermochemical and spectroscopic data, such as ionization energies (IEs), 0 K bond dissociation energies, 0 K heats of formation, and spectroscopic constants for radicals and molecules and their ions of relevance to combustion chemistry. Two unique, generally applicable vacuum ultraviolet (VUV) laser photoion-photoelectron apparatuses have been developed in our group, which have used for high-resolution photoionization, photoelectron, and photodissociation studies for many small molecules of combustion relevance.

Spin dynamics in relativistic ionization with highly charged ions in super-strong laser fields

International Nuclear Information System (INIS)

Klaiber, Michael; Yakaboylu, Enderalp; Bauke, Heiko; Hatsagortsyan, Karen Z; Müller, Carsten; Paulus, Gerhard G

2014-01-01

Spin dynamics and induced spin effects in above-threshold ionization of hydrogenlike highly charged ions in super-strong laser fields are investigated. Spin-resolved ionization rates in the tunnelling regime are calculated by employing two versions of a relativistic Coulomb-corrected strong-field approximation (SFA). An intuitive simpleman model is developed which explains the derived scaling laws for spin flip and spin asymmetry effects. The intuitive model as well as our ab initio numerical simulations support the analytical results for the spin effects obtained in the dressed SFA where the impact of the laser field on the electron spin evolution in the bound state is taken into account. In contrast, the standard SFA is shown to fail in reproducing spin effects in ionization even at a qualitative level. The anticipated spin-effects are expected to be measurable with modern laser techniques combined with an ion storage facility. (paper)

Selective detection of isomers with photoionization mass spectrometry for studies of hydrocarbon flame chemistry

International Nuclear Information System (INIS)

Cool, Terrill A.; Nakajima, Koichi; Mostefaoui, Toufik A.; Qi, Fei; McIlroy, Andrew; Westmoreland, Phillip R.; Law, Matthew E.; Poisson, Lionel; Peterka, Darcy S.; Ahmed, Musahid

2003-01-01

We report the first use of synchrotron radiation, continuously tunable from 8 to 15 eV, for flame-sampling photoionization mass spectrometry (PIMS). Synchrotron radiation offers important advantages over the use of pulsed vacuum ultraviolet lasers for PIMS; these include superior signal-to-noise, soft ionization, and access to photon energies outside the limited tuning ranges of current VUV laser sources. Near-threshold photoionization efficiency measurements were used to determine the absolute concentrations of the allene and propyne isomers of C 3 H 4 in low-pressure laminar ethylene-oxygen and benzene-oxygen flames. Similar measurements of the isomeric composition of C 2 H 4 O species in a fuel-rich ethylene-oxygen flame revealed the presence of substantial concentrations of ethenol (vinyl alcohol) and acetaldehyde. Ethenol has not been previously detected in hydrocarbon flames. Absolute photoionization cross sections were measured for ethylene, allene, propyne, and acetaldehyde, using propene as a calibration standard. PIE curves are presented for several additional reaction intermediates prominent in hydrocarbon flames

Rapid ionization of the environment of SN 1987A

International Nuclear Information System (INIS)

Raga, A.C.

1987-01-01

It has been suggested by some authors that IUE observations of the supernova SN 1987A show the presence of a strong component of the interstellar C IV 1550 and Si IV 1393 absorption lines at a velocity that approximately corresponds to the velocity of the LMC. It is possible that this component might come from originally neutral (or at least not very highly ionized) gas which has been photoionized by the initially very strong ionizing radiation field of the supernova. Theoretical considerations of this scenario lead to the study of fast (with velocities of about c) ionization fronts. It is shown that for reasonable model parameters it is possible to obtain considerably large C IV column densities, in agreement with the IUE observations. On the other hand, the models do not so easily predict the large Si IV column densities that are also obtained from the IUE observations. It is found that only models in which the interstellar medium surrounding SN 1987A is initially composed of already ionized hydrogen and helium predict substantial Si IV column densities. This result provides an interesting prediction of the ionization state of the environment of the presupernova star. 9 references

Rapid ionization of the environment of SN 1987A

Science.gov (United States)

Raga, A. C.

1987-01-01

It has been suggested by some authors that IUE observations of the supernova SN 1987A show the presence of a strong component of the interstellar C IV 1550 and Si IV 1393 absorption lines at a velocity that approximately corresponds to the velocity of the LMC. It is possible that this component might come from originally neutral (or at least not very highly ionized) gas which has been photoionized by the initially very strong ionizing radiation field of the supernova. Theoretical considerations of this scenario lead to the study of fast (with velocities of about c) ionization fronts. It is shown that for reasonable model parameters it is possible to obtain considerably large C IV column densities, in agreement with the IUE observations. On the other hand, the models do not so easily predict the large Si IV column densities that are also obtained from the IUE observations. It is found that only models in which the interstellar medium surrounding SN 1987A is initially composed of already ionized hydrogen and helium predict substantial Si IV column densities. This result provides an interesting prediction of the ionization state of the environment of the presupernova star.

Gas chromatography coupled to atmospheric pressure ionization mass spectrometry (GC-API-MS): Review

International Nuclear Information System (INIS)

Li, Du-Xin; Gan, Lin; Bronja, Amela; Schmitz, Oliver J.

2015-01-01

Although the coupling of GC/MS with atmospheric pressure ionization (API) has been reported in 1970s, the interest in coupling GC with atmospheric pressure ion source was expanded in the last decade. The demand of a “soft” ion source for preserving highly diagnostic molecular ion is desirable, as compared to the “hard” ionization technique such as electron ionization (EI) in traditional GC/MS, which fragments the molecule in an extensive way. These API sources include atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), atmospheric pressure laser ionization (APLI), electrospray ionization (ESI) and low temperature plasma (LTP). This review discusses the advantages and drawbacks of this analytical platform. After an introduction in atmospheric pressure ionization the review gives an overview about the history and explains the mechanisms of various atmospheric pressure ionization techniques used in combination with GC such as APCI, APPI, APLI, ESI and LTP. Also new developments made in ion source geometry, ion source miniaturization and multipurpose ion source constructions are discussed and a comparison between GC-FID, GC-EI-MS and GC-API-MS shows the advantages and drawbacks of these techniques. The review ends with an overview of applications realized with GC-API-MS. - Highlights: • Atmospheric pressure ion sources (APCI, ESI, APPI, APLC etc) enable the coupling of LC-based high-end MS to GC. • APIs show advantages in selectivity and sensitivity compared with EI in GC-MS. • Accurate mass database in GC-APCI/MS is emerging as an alternative to GC-EI/MS database.

Gas chromatography coupled to atmospheric pressure ionization mass spectrometry (GC-API-MS): Review

Energy Technology Data Exchange (ETDEWEB)

Li, Du-Xin; Gan, Lin; Bronja, Amela [University of Duisburg-Essen, Applied Analytical Chemistry, Universitaetsstr. 5-7, 45141 Essen (Germany); Schmitz, Oliver J., E-mail: oliver.schmitz@uni-due.de [University of Duisburg-Essen, Applied Analytical Chemistry, Universitaetsstr. 5-7, 45141 Essen (Germany)

2015-09-03

Although the coupling of GC/MS with atmospheric pressure ionization (API) has been reported in 1970s, the interest in coupling GC with atmospheric pressure ion source was expanded in the last decade. The demand of a “soft” ion source for preserving highly diagnostic molecular ion is desirable, as compared to the “hard” ionization technique such as electron ionization (EI) in traditional GC/MS, which fragments the molecule in an extensive way. These API sources include atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), atmospheric pressure laser ionization (APLI), electrospray ionization (ESI) and low temperature plasma (LTP). This review discusses the advantages and drawbacks of this analytical platform. After an introduction in atmospheric pressure ionization the review gives an overview about the history and explains the mechanisms of various atmospheric pressure ionization techniques used in combination with GC such as APCI, APPI, APLI, ESI and LTP. Also new developments made in ion source geometry, ion source miniaturization and multipurpose ion source constructions are discussed and a comparison between GC-FID, GC-EI-MS and GC-API-MS shows the advantages and drawbacks of these techniques. The review ends with an overview of applications realized with GC-API-MS. - Highlights: • Atmospheric pressure ion sources (APCI, ESI, APPI, APLC etc) enable the coupling of LC-based high-end MS to GC. • APIs show advantages in selectivity and sensitivity compared with EI in GC-MS. • Accurate mass database in GC-APCI/MS is emerging as an alternative to GC-EI/MS database.

The VIMOS Ultra Deep Survey: Nature, ISM properties, and ionizing spectra of CIII]λ1909 emitters at z = 2-4

Science.gov (United States)

Nakajima, K.; Schaerer, D.; Le Fèvre, O.; Amorín, R.; Talia, M.; Lemaux, B. C.; Tasca, L. A. M.; Vanzella, E.; Zamorani, G.; Bardelli, S.; Grazian, A.; Guaita, L.; Hathi, N. P.; Pentericci, L.; Zucca, E.

2018-05-01

Context. Ultraviolet (UV) emission-line spectra are used to spectroscopically confirm high-z galaxies and increasingly also to determine their physical properties. Aims: We construct photoionization models to interpret the observed UV spectra of distant galaxies in terms of the dominant radiation field and the physical condition of the interstellar medium (ISM). These models are applied to new spectroscopic observations from the VIMOS Ultra Deep Survey (VUDS). Methods: We construct a large grid of photoionization models, which use several incident radiation fields (stellar populations, active galactic nuclei (AGNs), mix of stars and AGNs, blackbodies, and others), and cover a wide range of metallicities and ionization parameters. From these models we derive new spectral UV line diagnostics using equivalent widths (EWs) of [CIII]λ1909 doublet, CIVλ1549 doublet and the line ratios of [CIII], CIV, and He IIλ1640 recombination lines. We apply these diagnostics to a sample of 450 [CIII]-emitting galaxies at redshifts z = 2-4 previously identified in VUDS. Results: We demonstrate that our photoionization models successfully reproduce observations of nearby and high-redshift sources with known radiation field and/or metallicity. For star-forming galaxies our models predict that [CIII] EW peaks at sub-solar metallicities, whereas CIV EW peaks at even lower metallicity. Using the UV diagnostics, we show that the average star-forming galaxy (EW([CIII]) 2 Å) based on the composite of the 450 UV-selected galaxies' spectra The inferred metallicity and ionization parameter is typically Z = 0.3-0.5 Z⊙ and logU = -2.7 to - 3, in agreement with earlier works at similar redshifts. The models also indicate an average age of 50-200 Myr since the beginning of the current star-formation, and an ionizing photon production rate, ξion, of logξion/erg-1 Hz = 25.3-25.4. Among the sources with EW([CIII]) >= 10 Å, approximately 30% are likely dominated by AGNs. The metallicity derived

Effects of ionizing radiation and steady magnetic field on erythrocytes

International Nuclear Information System (INIS)

Ivanov, S. P.; Galutzov, B. P.; Kuzmanova, M. A.; Markov, M. S.

1996-01-01

A complex biophysical test for studying the effects of ionizing and non-ionizing radiation has been developed. The following cell and membrane parameters have been investigated: cell size, cell shape, cell distribution by size, electrophoretic mobility, extent of hemolysis, membrane transport and membrane impedance. Gamma ray doses of 2.2 Gy and 3.3 Gy were used as ionizing radiation and steady (DC) magnetic field of 5-90 mT representing the non-ionizing radiation. Erythrocytes from humans and rats were exposed in vitro to both ionizing and non-ionizing radiation. In some experiments ionizing radiation was applied in vivo as well. Each of the simultaneously studied parameters have been found to change as a function of applied radiation. The proposed test allows an estimation of the changes in the elastic, rheological and electrical parameters of cells and biological membranes. Results indicate that ionizing radiation is significantly more effective in an in vivo application, while magnetic fields are more effective when applied in vitro. Surprisingly, steady magnetic fields were found to act as protector against some harmful effects of ionizing radiation. (authors)

Measurements of the Townsend first ionization coefficient in pure isobutane under uniform electric fields

International Nuclear Information System (INIS)

Petri, Anna Raquel

2013-01-01

In this work are presented data of Townsend first ionization coefficient, α, in pure isobutane, obtained with a parallel plate chamber of resistive anode, for the reduced electric field range of 140 Td up to 230 Td. The adopted method is based on a new version of the Pulsed Townsend Technique, where the primary ionization is produced by the incidence of nitrogen pulsed laser beam in an aluminum electrode (cathode). The glass anode of high resistivity (ρ = 2 x 10 12 Ω.cm) protects the detector against sparks. To validate the method, the α values were determined by comparing the ionization and avalanche electric currents in nitrogen, gas widely studied with well-established data in literature. This technique was successfully extended to obtain α parameters in pure isobutane. The presence of effects related to spatial charge, recombination and ohmic drop across the resistive anode was investigated by varying laser pulse repetition rate, its intensity and applied electric field. Of these secondary processes, only the ohmic drop was relevant and the reduced electric field values were corrected for it. The first Townsend coefficients obtained are compatible, within the experimental errors, with those determined with Magboltz 2 program versions 7.1 e 8.6. (author)

Coherent combs in ionization by intense and short laser pulses

Energy Technology Data Exchange (ETDEWEB)

Krajewska, K., E-mail: Katarzyna.Krajewska@fuw.edu.pl [Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warszawa (Poland); Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588-0299 (United States); Kamiński, J.Z., E-mail: Jerzy.Kaminski@fuw.edu.pl [Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warszawa (Poland)

2016-03-22

Photoionization of positive ions by a train of intense, short laser pulses is investigated within the relativistic strong field approximation, using the velocity gauge. The formation of broad peak structures in the high-energy domain of photoelectrons is observed and interpreted. The emergence of coherent photoelectron energy combs within these structures is demonstrated, and it is interpreted as the consequence of the Fraunhofer-type interference/diffraction of probability amplitudes of ionization from individual pulses comprising the train. Extensions to the coherent angular combs are also studied, and effects related to the radiation pressure are presented. - Highlights: • We develop relativistic Strong-Field Approximation for ionization by intense and short laser pulses of arbitrary spectral compositions. • We show that the consistent interpretation of results is provided by the Keldysh-type saddle point analysis of probability amplitudes. • We derive a general Fraunhofer-type interference/diffraction formula for finite train of pulses. • We study the coherent combs in photoelectron probability distributions.

Atomic and molecular resonance ionization

International Nuclear Information System (INIS)

Botter, R.; Petit, A.

1990-01-01

Published in summary form only the paper recalls the principle of resonance photoionization, transition probability, selectivity and critical parameters. Examples of applications are briefly treated: Trace analysis by resonance ionization mass spectroscopy for detection of Fe in Zr F 4 for fabrication of optical fibers and laser isotopic separation of U 235 and Gd 157 [fr

Photoionization microscopy: Hydrogenic theory in semiparabolic coordinates and comparison with experimental results

Science.gov (United States)

Kalaitzis, P.; Danakas, S.; Lépine, F.; Bordas, C.; Cohen, S.

2018-05-01

Photoionization microscopy (PM) is an experimental method allowing for high-resolution measurements of the electron current probability density in the case of photoionization of an atom in an external uniform static electric field. PM is based on high-resolution velocity-map imaging and offers the unique opportunity to observe the quantum oscillatory spatial structure of the outgoing electron flux. We present the basic elements of the quantum-mechanical theoretical framework of PM for hydrogenic systems near threshold. Our development is based on the computationally more convenient semiparabolic coordinate system. Theoretical results are first subjected to a quantitative comparison with hydrogenic images corresponding to quasibound states and a qualitative comparison with nonresonant images of multielectron atoms. Subsequently, particular attention is paid on the structure of the electron's momentum distribution transversely to the static field (i.e., of the angularly integrated differential cross-section as a function of electron energy and radius of impact on the detector). Such 2D maps provide at a glance a complete picture of the peculiarities of the differential cross-section over the entire near-threshold energy range. Hydrogenic transverse momentum distributions are computed for the cases of the ground and excited initial states and single- and two-photon ionization schemes. Their characteristics of general nature are identified by comparing the hydrogenic distributions among themselves, as well as with a presently recorded experimental distribution concerning the magnesium atom. Finally, specificities attributed to different target atoms, initial states, and excitation scenarios are also discussed, along with directions of further work.

Absolute partial photoionization cross sections of ethylene

Science.gov (United States)

Grimm, F. A.; Whitley, T. A.; Keller, P. R.; Taylor, J. W.

1991-07-01

Absolute partial photoionization cross sections for ionization out of the first four valence orbitals to the X 2B 3u, A 2B 3g, B 2A g and C 2B 2u states of the C 2H 4+ ion are presented as a function of photon energy over the energy range from 12 to 26 eV. The experimental results have been compared to previously published relative partial cross sections for the first two bands at 18, 21 and 24 eV. Comparison of the experimental data with continuum multiple scattering Xα calculations provides evidence for extensive autoionization to the X 2B 3u state and confirms the predicted shape resonances in ionization to the A 2B 3g and B 2A g states. Identification of possible transitions for the autoionizing resonances have been made using multiple scattering transition state calculations on Rydberg excited states.

Photoionization and Recombination

Science.gov (United States)

Nahar, Sultana N.

2000-01-01

Theoretically self-consistent calculations for photoionization and (e + ion) recombination are described. The same eigenfunction expansion for the ion is employed in coupled channel calculations for both processes, thus ensuring consistency between cross sections and rates. The theoretical treatment of (e + ion) recombination subsumes both the non-resonant recombination ("radiative recombination"), and the resonant recombination ("di-electronic recombination") processes in a unified scheme. In addition to the total, unified recombination rates, level-specific recombination rates and photoionization cross sections are obtained for a large number of atomic levels. Both relativistic Breit-Pauli, and non-relativistic LS coupling, calculations are carried out in the close coupling approximation using the R-matrix method. Although the calculations are computationally intensive, they yield nearly all photoionization and recombination parameters needed for astrophysical photoionization models with higher precision than hitherto possible, estimated at about 10-20% from comparison with experimentally available data (including experimentally derived DR rates). Results are electronically available for over 40 atoms and ions. Photoionization and recombination of He-, and Li-like C and Fe are described for X-ray modeling. The unified method yields total and complete (e+ion) recombination rate coefficients, that can not otherwise be obtained theoretically or experimentally.

Resonant excitation and the decay of autoionization states in a strong electromagnetic field

International Nuclear Information System (INIS)

Andryushin, A.I.; Kazakov, A.E.; Fedorov, M.V.

1985-01-01

Photoionization of atoms involving resonant excitation of the auto-ionization state is studied. The evolution of the total ionization probability, its dependence on the frequency of the resonance radiation and also the photoelectron energy spectrum are investigated. It is shown that the energy of the final state of the system may be localized either in the vicinity of E approximately Esub(α), where Esub(α) is the auto-ionization energy, or in the vicinity of E approximately Esub(α)+h/2πω where h/2πω is the quantum energy of the resonance radiation. The photoelectron specturum in the region E approximately Esub(α)+h/2πω as a whole is similar to the electron spectrum on photoionization of atoms involving resonance excitation of the bound state. A strong effect on the photoelectron spectrum in the region E approximately Esub(α) is exerted by interference of various decay channels of the ground state in the resonance field which leads to the appearance in the spectrum of a characteristic structure of the Fano type. Interence also affects the widths of the two spectral curves, the relatve amount of electrons in the two energy ranges and also other characteristics of the ionization process. It is shown that the presence of a noninterfering photoionization channel of the autoionization state ensures the finiteness of the swidths and heights of the spectral curves and the absence of complete ''coherency merging''

Finite element modelling of ionized field quantities around a monopolar HVDC transmission line

International Nuclear Information System (INIS)

Jaiswal, Vinay; Thomas, M Joy

2003-01-01

In this paper, the Poisson's equation describing the ionized field around an HVDC line is solved using an improved finite element based technique. First order isoparametric quadrilateral elements, together with a modified updating criterion for the space charge distribution, are implemented in the iterative procedure. A novel technique is presented for mesh generation in the presence of space charges. Electric field lines and equipotential lines have been computed using the proposed technique. Total corona current at different applied voltages above corona onset voltage, electric field at the ground plane with and without the presence of space charges and current density at the ground plane have also been computed. The results are in agreement with the experimental values available in the published literature

Coupled-cluster treatment of molecular strong-field ionization

Science.gov (United States)

Jagau, Thomas-C.

2018-05-01

Ionization rates and Stark shifts of H2, CO, O2, H2O, and CH4 in static electric fields have been computed with coupled-cluster methods in a basis set of atom-centered Gaussian functions with a complex-scaled exponent. Consideration of electron correlation is found to be of great importance even for a qualitatively correct description of the dependence of ionization rates and Stark shifts on the strength and orientation of the external field. The analysis of the second moments of the molecular charge distribution suggests a simple criterion for distinguishing tunnel and barrier suppression ionization in polyatomic molecules.

Fluctuation charge effects in ionization fronts

International Nuclear Information System (INIS)

Arrayas, Manuel; Trueba, Jose L; Baltanas, J P

2008-01-01

In this paper, we study the effects of charge fluctuations on the propagation of both negative and positive ionization fronts in streamer discharges. We show that fronts accelerate when random charge creation events are present. This effect might play a similar role to photoionization in order to make the front move faster

Fluctuation charge effects in ionization fronts

Energy Technology Data Exchange (ETDEWEB)

Arrayas, Manuel; Trueba, Jose L [Area de Electromagnetismo, Universidad Rey Juan Carlos, Camino del Molino s/n, 28943 Fuenlabrada, Madrid (Spain); Baltanas, J P [Departamento de Fisica Aplicada II, Universidad de Sevilla, Av. Reina Mercedes 2, 41012 Sevilla (Spain)

2008-05-21

In this paper, we study the effects of charge fluctuations on the propagation of both negative and positive ionization fronts in streamer discharges. We show that fronts accelerate when random charge creation events are present. This effect might play a similar role to photoionization in order to make the front move faster.

Vacuum ultraviolet photoionization of carbohydrates and nucleotides

Energy Technology Data Exchange (ETDEWEB)

Shin, Joong-Won, E-mail: jshin@govst.edu [Division of Science, Governors State University, University Park, Illinois 60484-0975 (United States); Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872 (United States); Bernstein, Elliot R., E-mail: erb@lamar.colostate.edu [Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872 (United States)

2014-01-28

Carbohydrates (2-deoxyribose, ribose, and xylose) and nucleotides (adenosine-, cytidine-, guanosine-, and uridine-5{sup ′}-monophosphate) are generated in the gas phase, and ionized with vacuum ultraviolet photons (VUV, 118.2 nm). The observed time of flight mass spectra of the carbohydrate fragmentation are similar to those observed [J.-W. Shin, F. Dong, M. Grisham, J. J. Rocca, and E. R. Bernstein, Chem. Phys. Lett. 506, 161 (2011)] for 46.9 nm photon ionization, but with more intensity in higher mass fragment ions. The tendency of carbohydrate ions to fragment extensively following ionization seemingly suggests that nucleic acids might undergo radiation damage as a result of carbohydrate, rather than nucleobase fragmentation. VUV photoionization of nucleotides (monophosphate-carbohydrate-nucleobase), however, shows that the carbohydrate-nucleobase bond is the primary fragmentation site for these species. Density functional theory (DFT) calculations indicate that the removed carbohydrate electrons by the 118.2 nm photons are associated with endocyclic C–C and C–O ring centered orbitals: loss of electron density in the ring bonds of the nascent ion can thus account for the observed fragmentation patterns following carbohydrate ionization. DFT calculations also indicate that electrons removed from nucleotides under these same conditions are associated with orbitals involved with the nucleobase-saccharide linkage electron density. The calculations give a general mechanism and explanation of the experimental results.

Vacuum ultraviolet photoionization of carbohydrates and nucleotides

International Nuclear Information System (INIS)

Shin, Joong-Won; Bernstein, Elliot R.

2014-01-01

Carbohydrates (2-deoxyribose, ribose, and xylose) and nucleotides (adenosine-, cytidine-, guanosine-, and uridine-5 ′ -monophosphate) are generated in the gas phase, and ionized with vacuum ultraviolet photons (VUV, 118.2 nm). The observed time of flight mass spectra of the carbohydrate fragmentation are similar to those observed [J.-W. Shin, F. Dong, M. Grisham, J. J. Rocca, and E. R. Bernstein, Chem. Phys. Lett. 506, 161 (2011)] for 46.9 nm photon ionization, but with more intensity in higher mass fragment ions. The tendency of carbohydrate ions to fragment extensively following ionization seemingly suggests that nucleic acids might undergo radiation damage as a result of carbohydrate, rather than nucleobase fragmentation. VUV photoionization of nucleotides (monophosphate-carbohydrate-nucleobase), however, shows that the carbohydrate-nucleobase bond is the primary fragmentation site for these species. Density functional theory (DFT) calculations indicate that the removed carbohydrate electrons by the 118.2 nm photons are associated with endocyclic C–C and C–O ring centered orbitals: loss of electron density in the ring bonds of the nascent ion can thus account for the observed fragmentation patterns following carbohydrate ionization. DFT calculations also indicate that electrons removed from nucleotides under these same conditions are associated with orbitals involved with the nucleobase-saccharide linkage electron density. The calculations give a general mechanism and explanation of the experimental results

Femtosecond Light Source for Phase-Controlled Multiphoton Ionization

International Nuclear Information System (INIS)

Sokolov, A. V.; Walker, D. R.; Yavuz, D. D.; Yin, G. Y.; Harris, S. E.

2001-01-01

We describe a femtosecond Raman light source with more than an octave of optical bandwidth. We use this source to demonstrate phase control of multiphoton ionization under conditions where ionization requires eleven photons of the lowest frequency of the spectrum or five photons of the highest frequency. The nonlinearity of the photoionization process allows us to characterize the light source. Experiment-to-theory comparison implies generation of a near single-cycle waveform

Ionization waves caused by the effects of a magnetic field

International Nuclear Information System (INIS)

Miura, Kosuke; Imazu, Shingo

1980-01-01

The self-excited ionization waves was observed in the Ne positive column. The experiments were made for Ne gas from 0.07 to 1.0 Torr, with the magnetic field from 0 to 3.33 kG. The discharge current were 10 to 300 mA. The longitudinal magnetic field was made by an air-core solenoid coil. The axial electric field was measured by two wall probes. The frequency, wave length and amplitude of waves were measured with a photo multiplier. It was found that the longitudinal magnetic field caused new self-excited ionization waves. The frequency of these waves decreased monotonously with increasing field. The behaviors of the wave length and amplitude were complicate, and the cause of these phenomena is related to the ionization waves due to the spatial resonance of electron gas, namely s-waves, p-waves and fluid γ-waves. The threshold of the magnetic field to cause the ionization waves increased with increasing gas pressure, and with decreasing discharge current in the range 0.07 to 0.44 Torr. The frequency of the self-excited ionization waves occurred at zero field was almost constant in the field-frequency relation. A simple dispersion equation was derived, and the Novak constant can be introduced. (J.P.N.)

Imaging photoelectron photoion coincidence spectroscopy with velocity focusing electron optics

International Nuclear Information System (INIS)

Bodi, Andras; Johnson, Melanie; Gerber, Thomas; Gengeliczki, Zsolt; Sztaray, Balint; Baer, Tomas

2009-01-01

An imaging photoelectron photoion coincidence spectrometer at the vacuum ultraviolet (VUV) beamline of the Swiss Light Source is presented and a few initial measurements are reported. Monochromatic synchrotron VUV radiation ionizes the cooled or thermal gas-phase sample. Photoelectrons are velocity focused, with better than 1 meV resolution for threshold electrons, and also act as start signal for the ion time-of-flight analysis. The ions are accelerated in a relatively low, 40-80 V cm -1 field, which enables the direct measurement of rate constants in the 10 3 -10 7 s -1 range. All electron and ion events are recorded in a triggerless multiple-start/multiple-stop setup, which makes it possible to carry out coincidence experiments at >100 kHz event frequencies. As examples, the threshold photoelectron spectrum of the argon dimer and the breakdown diagrams for hydrogen atom loss in room temperature methane and the chlorine atom loss in cold chlorobenzene are shown and discussed.

Local clouds ionization, temperatures, electron densities and interfaces, from GHRS and IMAPS spectra of epsilon Canis Majoris

CERN Document Server

Gry, C; Gry, Cecile; Jenkins, Edward B.

2001-01-01

The composition and physical properties of several local clouds, including the Local Interstellar Cloud (LIC) in which the Sun is embedded, are derived from absorption features in the UV spectrum of the star epsilon CMa. We derive temperatures and densities for three components by combining our interpretations of the ionization balance of magnesium and the relative population of C II in an excited fine-structure level. We find that for the LIC n(e) = 0.12 +/-0.05 cm-3 and T = 7000 +/-1200 K. We derive the ionization fractions of hydrogen and discuss the ionizing processes. In particular the hydrogen and helium ionizations in the LIC are compatible with photoionization by the local EUV radiation fields from the hot stars and the cloud interface with the hot gas. We confirm the detection of high ionization species : Si III is detected in all clouds and C IV in two of them, including the LIC, suggesting the presence of ionized interfaces around the local clouds.

Rydberg atoms ionization by microwave field and electromagnetic pulses

International Nuclear Information System (INIS)

Kaulakys, B.; Vilutis, G.

1995-01-01

A simple theory of the Rydberg atoms ionization by electromagnetic pulses and microwave field is presented. The analysis is based on the scale transformation which reduces the number of parameters and reveals the functional dependencies of the processes. It is shown that the observed ionization of Rydberg atoms by subpicosecond electromagnetic pulses scale classically. The threshold electric field required to ionise a Rydberg state may be simply evaluated in the photonic basis approach for the quantum dynamics or from the multiphoton ionization theory

Effect of negative ions on current growth and ionizing wave propagation in air

International Nuclear Information System (INIS)

Kline, L.E.

1975-01-01

The spatiotemporal development of electron and ion densities, electric fields, and luminosity are calculated for electron pulse experiments in overvolted parallel-plane gaps by numerically solving continuity equations together with Poisson's equation. Experimental coefficients for primary ionization, cathode photoemission, photoionization, and luminosity are used. Unambiguous determination of the coefficients for attachment, detachment, and charge transfer is not possible from available experimental results. Therefore, the calculations are repeated for three sets of coefficients for these processes, corresponding to the following assumptions: unstable negative ions, stable negative ions, and no negative ions. The results of the calculations show, in each case, that the electron pulse initiates an avalanche which grows exponentially until the onset of space-charge effects. The calculated growth rate is strongly affected by the assumed attachment, detachment, and charge-transfer coefficients. When the total number of electrons in the avalanche reaches approx.10 8 , anode- and cathode-directed ionizing waves, or streamers, develop from the avalanche and produce a weakly ionized filamentary plasma. The calculated ionizing wave velocities are strongly increasing functions of the space-charge--enhanced electric field within the waves and are insensitive to the assumed attachment, detachment, and charge-transfer coefficients. The numerically calculated ionizing wave velocities are in approximate agreement with a simple analytical theory

X-ray heating of laboratory photoionized plasmas at Z

Science.gov (United States)

Mancini, R.; Lockard, T.; Mayes, D.; Loisel, G.; Bailey, J.; Rochau, G.; Abdallah, J.; Fontes, C.; Liedahl, D.; Golovkin, I.

2017-10-01

In separate experiments performed at the Z facility of Sandia National Laboratories two different samples were employed to produce and characterize photoionized plasmas. One was a gas cell filled with neon, and the other was a thin silicon layer coated with plastic. Both samples were driven by the broadband x-ray flux produced at the collapse of a wire array z-pinch implosion. Transmission spectroscopy of a narrowband portion of the x-ray flux was used to diagnose the charge state distribution, and the electron temperature was extracted from a Li-like ion level population ratio. To interpret the temperature measurement, we performed Boltzmann kinetics and radiation-hydrodynamic simulations. We found that non-equilibrium atomic physics and the coupling of the radiation flux to the level population kinetics play a critical role in modeling the x-ray heating of photoionized plasmas. In spite of being driven by similar x-ray drives, differences of ionization and charged state distributions in the neon and silicon plasmas are reflected in the plasma heating and observed temperatures. DOE OFES Grant DE-SC0014451 and ZFSP.

Fine- and hyperfine-structure effects in molecular photoionization. I. General theory and direct photoionization

Energy Technology Data Exchange (ETDEWEB)

Germann, Matthias; Willitsch, Stefan, E-mail: stefan.willitsch@unibas.ch [Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel (Switzerland)

2016-07-28

We develop a model for predicting fine- and hyperfine intensities in the direct photoionization of molecules based on the separability of electron and nuclear spin states from vibrational-electronic states. Using spherical tensor algebra, we derive highly symmetrized forms of the squared photoionization dipole matrix elements from which we derive the salient selection and propensity rules for fine- and hyperfine resolved photoionizing transitions. Our theoretical results are validated by the analysis of the fine-structure resolved photoelectron spectrum of O{sub 2} reported by Palm and Merkt [Phys. Rev. Lett. 81, 1385 (1998)] and are used for predicting hyperfine populations of molecular ions produced by photoionization.

Fine- and hyperfine-structure effects in molecular photoionization. I. General theory and direct photoionization.

Science.gov (United States)

Germann, Matthias; Willitsch, Stefan

2016-07-28

We develop a model for predicting fine- and hyperfine intensities in the direct photoionization of molecules based on the separability of electron and nuclear spin states from vibrational-electronic states. Using spherical tensor algebra, we derive highly symmetrized forms of the squared photoionization dipole matrix elements from which we derive the salient selection and propensity rules for fine- and hyperfine resolved photoionizing transitions. Our theoretical results are validated by the analysis of the fine-structure resolved photoelectron spectrum of O2 reported by Palm and Merkt [Phys. Rev. Lett. 81, 1385 (1998)] and are used for predicting hyperfine populations of molecular ions produced by photoionization.

Single Photon Double Ionization of Atomic Oxygen

Science.gov (United States)

Wickramarathna, Madhushani; Gorczyca, Thomas; Ballance, Connor; Stolte, Wayne

2017-04-01

Single photon double ionization cross sections are calculated using an R-matrix with pseudostates (RMPS) method which was recently applied by Gorczyca et al. for the double photoionization of helium. With the convergence of these theoretical calculations for the simple case of helium, we extend this methodology to consider the more complex case of oxygen double photoionization. We compare our calculated results with recent measurements at the Advanced Light Source, as well as earlier experimental measurements. Our RMPS results agree well, qualitatively, with the experimental measurements, but there exist outstanding discrepancies to be addressed. This project is supported by NASA APRA award NNX17AD41G.

Photoionization behavior of Eu2+-doped BaMgSiO4 long-persisting phosphor upon UV irradiation

International Nuclear Information System (INIS)

Li, Y.; Wang, Y.; Gong, Y.; Xu, X.; Zhang, F.

2011-01-01

Highlights: → Photoionization behavior of BaMgSiO 4 :Eu 2+ long persistent phosphor upon UV irradiation. → Green phosphorescence was obtained from BaMgSiO 4 :Eu 2+ . → The ionization of Eu 2+ to Eu 3+ was observed in BaMgSiO 4 :Eu 2+ . → The photogenerated Eu 3+ cannot change back to its divalent state at room temperature. → The phosphorescence is associated with the formation forming Eu 3+ -e - pairs. - Abstract: The fluorescence, phosphorescence and thermoluminescence properties of Eu-doped BaMgSiO 4 phosphors sintered in air and in a reducing atmosphere were investigated. Phosphorescence of phosphor sintered in a reducing atmosphere can last for 1.5 h at a recognizable intensity level, whereas phosphorescence of air-sintered phosphor can only persist for 6 min. In addition, a distinction between the shape of the fluorescence spectrum and its corresponding phosphorescence spectrum is observed in the former case. Ionization of Eu 2+ to Eu 3+ upon UV irradiation is observed in the phosphor prepared in a reducing atmosphere, but there is no indication that the photogenerated Eu 3+ cannot change back to its divalent state at room temperature after the excitation source is switched off. In addition, phosphor sintered in a reducing atmosphere shows photochromism upon UV irradiation. No such photoionization and photochromism behavior is observed for the air-sintered phosphor. A possible Eu 2+ photoionization mechanism is constructed on the basis of these experimental observations. The photoionization mechanism presented can also successfully explain the fluorescence and phosphorescence behavior of Eu in BaMgSiO 4 .

Imaging photoelectrons formed in strong laser fields

International Nuclear Information System (INIS)

Helm, H.; Dyer, M.J.; Saeed, M.; Huestis, D.L.

1993-01-01

An instrument capable of characterizing the angular correlation and energy distribution of products from photoionization of single atoms or molecules will be described. An external electric field is used to project individual charged particles generated in multiphoton ionization from the focal volume onto two-dimensional detectors. Digital images are recorded for each laser shot and summed. These images provide a direct view of the angular nodal plants of the photoelectrons and they can be analyzed to represent the spatial and energy distributions in the form of a polar plot, f(E,Θ). We discuss the application of this instrument to short pulse photoionization of rare gases and molecular hydrogen at visible and UV wavelengths at intensities ranging from 10 13 to 10 15 W/cm 2

Photoabsorption and S 2p photoionization of the SF6 molecule: resonances in the excitation energy range of 200-280 eV.

Science.gov (United States)

Stener, M; Bolognesi, P; Coreno, M; O'Keeffe, P; Feyer, V; Fronzoni, G; Decleva, P; Avaldi, L; Kivimäki, A

2011-05-07

Photoabsorption and S 2p photoionization of the SF(6) molecule have been studied experimentally and theoretically in the excitation energy range up to 100 eV above the S 2p ionization potentials. In addition to the well-known 2t(2g) and 4e(g) shape resonances, the spin-orbit-resolved S 2p photoionization cross sections display two weak resonances between 200 and 210 eV, a wide resonance around 217 eV, a Fano-type resonance around 240 eV, and a second wide resonance around 260 eV. Calculations based on time-dependent density functional theory allow us to assign the 217-eV and 260-eV features to the shape resonances in S 2p photoionization. The Fano resonance is caused by the interference between the direct S 2p photoionization channel and the resonant channel that results from the participator decay of the S 2s(-1)6t(1u) excited state. The weak resonances below 210-eV photon energy, not predicted by theory, are tentatively suggested to originate from the coupling between S 2p shake-up photoionization and S 2p single-hole photoionization. The experimental and calculated angular anisotropy parameters for S 2p photoionization are in good agreement.

A compact neutron generator using a field ionization source.

Science.gov (United States)

Persaud, Arun; Waldmann, Ole; Kapadia, Rehan; Takei, Kuniharu; Javey, Ali; Schenkel, Thomas

2012-02-01

Field ionization as a means to create ions for compact and rugged neutron sources is pursued. Arrays of carbon nano-fibers promise the high field-enhancement factors required for efficient field ionization. We report on the fabrication of arrays of field emitters with a density up to 10(6) tips∕cm(2) and measure their performance characteristics using electron field emission. The critical issue of uniformity is discussed, as are efforts towards coating the nano-fibers to enhance their lifetime and surface properties.

Vacuum ultraviolet photoionization mass spectrometric study of cyclohexene.

Science.gov (United States)

Chen, Jun; Cao, Maoqi; Wei, Bin; Ding, Mengmeng; Shan, Xiaobin; Liu, Fuyi; Sheng, Liusi

2016-02-01

In this work, photoionization and dissociation of cyclohexene have been studied by means of coupling a reflectron time-of-flight mass spectrometer with the tunable vacuum ultraviolet (VUV) synchrotron radiation. The adiabatic ionization energy of cyclohexene as well as the appearance energies of its fragment ions C6 H9 (+) , C6 H7 (+) , C5 H7 (+) , C5 H5 (+) , C4 H6 (+) , C4 H5 (+) , C3 H5 (+) and C3 H3 (+) were derived from the onset of the photoionization efficiency (PIE) curves. The optimized structures for the transition states and intermediates on the ground state potential energy surfaces related to photodissociation of cyclohexene were characterized at the ωB97X-D/6-31+g(d,p) level. The coupled cluster method, CCSD(T)/cc-pVTZ, was employed to calculate the corresponding energies with the zero-point energy corrections by the ωB97X-D/6-31+g(d,p) approach. Combining experimental and theoretical results, possible formation pathways of the fragment ions were proposed and discussed in detail. The retro-Cope rearrangement was found to play a crucial role in the formation of C4 H6 (+) , C4 H5 (+) and C3 H5 (+) . Intramolecular hydrogen migrations were observed as dominant processes in most of the fragmentation pathways of cyclohexene. The present research provides a clear picture of the photoionization and dissociation processes of cyclohexene in the 8- to 15.5-eV photon energy region. Copyright © 2016 John Wiley & Sons, Ltd.

Photoelectron wave function in photoionization: plane wave or Coulomb wave?

Science.gov (United States)

Gozem, Samer; Gunina, Anastasia O; Ichino, Takatoshi; Osborn, David L; Stanton, John F; Krylov, Anna I

2015-11-19

The calculation of absolute total cross sections requires accurate wave functions of the photoelectron and of the initial and final states of the system. The essential information contained in the latter two can be condensed into a Dyson orbital. We employ correlated Dyson orbitals and test approximate treatments of the photoelectron wave function, that is, plane and Coulomb waves, by comparing computed and experimental photoionization and photodetachment spectra. We find that in anions, a plane wave treatment of the photoelectron provides a good description of photodetachment spectra. For photoionization of neutral atoms or molecules with one heavy atom, the photoelectron wave function must be treated as a Coulomb wave to account for the interaction of the photoelectron with the +1 charge of the ionized core. For larger molecules, the best agreement with experiment is often achieved by using a Coulomb wave with a partial (effective) charge smaller than unity. This likely derives from the fact that the effective charge at the centroid of the Dyson orbital, which serves as the origin of the spherical wave expansion, is smaller than the total charge of a polyatomic cation. The results suggest that accurate molecular photoionization cross sections can be computed with a modified central potential model that accounts for the nonspherical charge distribution of the core by adjusting the charge in the center of the expansion.

Triggering Excimer Lasers by Photoionization from Corona Discharges

Science.gov (United States)

Xiong, Zhongmin; Duffey, Thomas; Brown, Daniel; Kushner, Mark

2009-10-01

High repetition rate ArF (192 nm) excimer lasers are used for photolithography sources in microelectronics fabrication. In highly attaching gas mixtures, preionization is critical to obtaining stable, reproducible glow discharges. Photoionization from a separate corona discharge is one technique for preionization which triggers the subsequent electron avalanche between the main electrodes. Photoionization triggering of an ArF excimer laser sustained in multi-atmosphere Ne/Ar/F2/Xe gas mixtures has been investigated using a 2-dimensional plasma hydrodynamics model including radiation transport. Continuity equations for charged and neutral species, and Poisson's equation are solved coincident with the electron temperature with transport coefficients obtained from solutions of Boltzmann's equation. Photoionizing radiation is produced by a surface discharge which propagates along a corona-bar located adjacent to the discharge electrodes. The consequences of pulse power waveform, corona bar location, capacitance and gas mixture on uniformity, symmetry and gain of the avalanche discharge will be discussed.

Ionization of colliding atoms the hard way and the easy way

International Nuclear Information System (INIS)

Jong, M.A.M. de.

1989-01-01

The photoionization of the He(2 1 , 3 S)/He collision system at thermic collision energy has been studied by measurement of the energy distribution of the photoelectrons and comparison of this with the one from spontaneous ionization, in particular transfer ionization during collisions between He ++ ions and Xenon atoms. (h;w). 119 refs.; 44 figs.; 78 schemes; 1 tab

An intense polarized beam by a laser ionization injection

International Nuclear Information System (INIS)

Ohmori, Chihiro; Hiramatsu, Shigenori; Nakamura, Takeshi.

1990-12-01

Accumulation of protons and polarized protons by photo-ionization injection are described. This method consists of (1)producing the neutral hydrogen beam by Lorentz stripping, (2)excitation of the neutral hydrogen beam with a laser, and (3)ionization of the hydrogen beam in the 2P excited state with another laser. When the laser for the excitation is circularly polarized, we can get a polarized proton beam. An ionization efficiency of 98% and a polarization of 80% can be expected by an intense laser beam from a FEL(Free Electron Laser). (author)

Modelling massive-star feedback with Monte Carlo radiation hydrodynamics: photoionization and radiation pressure in a turbulent cloud

Science.gov (United States)

Ali, Ahmad; Harries, Tim J.; Douglas, Thomas A.

2018-04-01

We simulate a self-gravitating, turbulent cloud of 1000M⊙ with photoionization and radiation pressure feedback from a 34M⊙ star. We use a detailed Monte Carlo radiative transfer scheme alongside the hydrodynamics to compute photoionization and thermal equilibrium with dust grains and multiple atomic species. Using these gas temperatures, dust temperatures, and ionization fractions, we produce self-consistent synthetic observations of line and continuum emission. We find that all material is dispersed from the (15.5pc)3 grid within 1.6Myr or 0.74 free-fall times. Mass exits with a peak flux of 2× 10-3M⊙yr-1, showing efficient gas dispersal. The model without radiation pressure has a slight delay in the breakthrough of ionization, but overall its effects are negligible. 85 per cent of the volume, and 40 per cent of the mass, become ionized - dense filaments resist ionization and are swept up into spherical cores with pillars that point radially away from the ionizing star. We use free-free emission at 20cm to estimate the production rate of ionizing photons. This is almost always underestimated: by a factor of a few at early stages, then by orders of magnitude as mass leaves the volume. We also test the ratio of dust continuum surface brightnesses at 450 and 850μ to probe dust temperatures. This underestimates the actual temperature by more than a factor of 2 in areas of low column density or high line-of-sight temperature dispersion; the HII region cavity is particularly prone to this discrepancy. However, the probe is accurate in dense locations such as filaments.

Imaging with Mass Spectrometry: A SIMS and VUV-Photoionization Study of Ion-Sputtered Atoms and Clusters from GaAs and Au

Energy Technology Data Exchange (ETDEWEB)

Takahashi, Lynelle; Zhou, Jia; Wilson, Kevin R.; Leone, Stephen R.; Ahmed, Musahid

2008-12-05

A new mass spectrometry surface imaging method is presented in which ion-sputtered neutrals are postionized by wavelength-tunable vacuum ultraviolet (VUV) light from a synchrotron source. Mass spectra and signal counts of the photoionized neutrals from GaAs (100) and Au are compared to those of the secondary ions. While clusters larger than dimers are more efficiently detected as secondary ions, certain species, such as As2, Au and Au2, are more efficiently detected through the neutral channel. Continuously tuning the photon wavelength allows photoionization efficiency (PIE) curves to be obtained for sputtered Asm (m=1,2) and Aun (n=1-4). From the observed ionization thresholds, sputtered neutral As and Au show no clear evidence of electronic excitation, while neutral clusters have photoionization onsets shifted to lower energies by ~;;0.3 eV. These shifts are attributed to unresolved vibrational and rotational excitations. High-spatial resolution chemical imaging with synchrotron VUV postionization is demonstrated at two different photon energies using a copper TEM grid embedded in indium. The resulting images are used to illustrate the use of tunable VUV light for verifying mass peak assignments by exploiting the unique wavelength-dependent PIE of each sputtered neutral species. This capability is valuable for identifying compounds when imaging chemically complex systems with mass spectrometry-based techniques.

Total OH reactivity measurements using a new fast Gas Chromatographic Photo-Ionization Detector (GC-PID

Directory of Open Access Journals (Sweden)

V. Sinha

2012-12-01

Full Text Available The primary and most important oxidant in the atmosphere is the hydroxyl radical (OH. Currently OH sinks, particularly gas phase reactions, are poorly constrained. One way to characterize the overall sink of OH is to measure directly the ambient loss rate of OH, the total OH reactivity. To date, direct measurements of total OH reactivity have been either performed using a Laser-Induced Fluorescence (LIF system ("pump-and-probe" or "flow reactor" or the Comparative Reactivity Method (CRM with a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS. Both techniques require large, complex and expensive detection systems. This study presents a feasibility assessment for CRM total OH reactivity measurements using a new detector, a Gas Chromatographic Photoionization Detector (GC-PID. Such a system is smaller, more portable, less power consuming and less expensive than other total OH reactivity measurement techniques.

Total OH reactivity is measured by the CRM using a competitive reaction between a reagent (here pyrrole with OH alone and in the presence of atmospheric reactive molecules. The new CRM method for total OH reactivity has been tested with parallel measurements of the GC-PID and the previously validated PTR-MS as detector for the reagent pyrrole during laboratory experiments, plant chamber and boreal field studies. Excellent agreement of both detectors was found when the GC-PID was operated under optimum conditions. Time resolution (60–70 s, sensitivity (LOD 3–6 s⁻¹ and overall uncertainty (25% in optimum conditions for total OH reactivity were similar to PTR-MS based total OH reactivity measurements. One drawback of the GC-PID system was the steady loss of sensitivity and accuracy during intensive measurements lasting several weeks, and a possible toluene interference. Generally, the GC-PID system has been shown to produce closely comparable results to the PTR-MS and thus in suitable environments (e.g. forests it

Effects of a static electric field on nonsequential double ionization

International Nuclear Information System (INIS)

Li Hongyun; Wang Bingbing; Li Xiaofeng; Fu Panming; Chen Jing; Liu Jie; Jiang Hongbing; Gong Qihuang; Yan Zongchao

2007-01-01

Using a three-dimensional semiclassical method, we perform a systematic analysis of the effects of an additional static electric field on nonsequential double ionization (NSDI) of a helium atom in an intense, linearly polarized laser field. It is found that the static electric field influences not only the ionization rate, but also the kinetic energy of the ionized electron returning to the parent ion, in such a way that, if the rate is increased, then the kinetic energy of the first returning electron is decreased, and vice versa. These two effects compete in NSDI. Since the effect of the static electric field on the ionization of the first electron plays a more crucial role in the competition, the symmetric double-peak structure of the He 2+ momentum distribution parallel to the polarization of the laser field is destroyed. Furthermore, the contribution of the trajectories with multiple recollisions to the NSDI is also changed dramatically by the static electric field. As the static electric field increases, the trajectories with two recollisions, which start at the time when the laser and the static electric field are in the same direction, become increasingly important for the NSDI

Photoionization in the Precursor of Laser Supported Detonation by Ultraviolet Radiation

International Nuclear Information System (INIS)

Shimamura, Kohei; Michigami, Keisuke; Wang, Bin; Komurasaki, Kimiya; Arakawa, Yoshihiro

2011-01-01

The propagation mechanism of laser-supported detonation (LSD) is important for designing laser propulsion for a detonation type thruster. The purpose of this work to was to confirm that photo-ionization in precursor is the predominant LSD sustainment mechanism. First of all, we tried to investigate the dependency of LSD duration on ambient gas species, air and argon. We took a series of high-speed images using the laser shadow-graphy. Besides, to estimate the UV photons emitted from the plasma, we used plasma emission spectroscopy and determined the electron temperature and density. As a result, the LSD duration of argon plasma and air plasma are 0.7 μs and 0.3 μs, resp. Besides, argon plasma emitted 10 10 to 10 14 photons/seconds, which was higher than air plasma. These results reveal that LSD propagation depends on the photon-contributing photoionization. The threshold photon-emission rate of LSD termination gives the elucidation of the LSD termination condition.

Interplay between Coulomb-focusing and non-dipole effects in strong-field ionization with elliptical polarization

Science.gov (United States)

Daněk, J.; Klaiber, M.; Hatsagortsyan, K. Z.; Keitel, C. H.; Willenberg, B.; Maurer, J.; Mayer, B. W.; Phillips, C. R.; Gallmann, L.; Keller, U.

2018-06-01

We study strong-field ionization and rescattering beyond the long-wavelength limit of the dipole approximation with elliptically polarized mid-IR laser pulses. Full three-dimensional photoelectron momentum distributions (PMDs) measured with velocity map imaging and tomographic reconstruction revealed an unexpected sharp ridge structure in the polarization plane (2018 Phys. Rev. A 97 013404). This thin line-shaped ridge structure for low-energy photoelectrons is correlated with the ellipticity-dependent asymmetry of the PMD along the beam propagation direction. The peak of the projection of the PMD onto the beam propagation axis is shifted from negative to positive values when the sharp ridge fades away with increasing ellipticity. With classical trajectory Monte Carlo simulations and analytical analysis, we study the underlying physics of this feature. The underlying physics is based on the interplay between the lateral drift of the ionized electron, the laser magnetic field induced drift in the laser propagation direction, and Coulomb focusing. To apply our observations to emerging techniques relying on strong-field ionization processes, including time-resolved holography and molecular imaging, we present a detailed classical trajectory-based analysis of our observations. The analysis leads to the explanation of the fine structure of the ridge and its non-dipole behavior upon rescattering while introducing restrictions on the ellipticity. These restrictions as well as the ionization and recollision phases provide additional observables to gain information on the timing of the ionization and recollision process and non-dipole properties of the ionization process.

Analysis of 62 synthetic cannabinoids by gas chromatography-mass spectrometry with photoionization.

Science.gov (United States)

Akutsu, Mamoru; Sugie, Ken-Ichi; Saito, Koichi

2017-01-01

Gas chromatography-mass spectrometry (GC-MS) in electron ionization (EI) mode is one of the most commonly used techniques for analysis of synthetic cannabinoids, because the GC-EI-MS spectra contain characteristic fragment ions for identification of a compound; however, the information on its molecular ions is frequently lacking. To obtain such molecular ion information, GC-MS in chemical ionization (CI) mode is frequently used. However, GC-CI-MS requires a relatively tedious process using reagent gas such as methane or isobutane. In this study, we show that GC-MS in photoionization (PI) mode provided molecular ions in all spectra of 62 synthetic cannabinoids, and 35 of the 62 compounds showed only the molecular radical cations. Except for the 35 compounds, the PI spectra showed very simple patterns with the molecular peak plus only a few fragment peak(s). An advantage is that the ion source for GC-PI-MS can easily be used for GC-EI-MS as well. Therefore, GC-EI/PI-MS will be a useful tool for the identification of synthetic cannabinoids contained in a dubious product. To the best of our knowledge, this is the first report to use GC-PI-MS for analysis of synthetic cannabinoids.

The ratio of double to single ionization of helium: The relationship of photon and bare charged particle impact ionization

International Nuclear Information System (INIS)

Manson, S.T.

1994-01-01

In this paper the author derives expressions for the ratio of double to single ionization of helium from its ground state, by both single photons, and charged particle impact. He shows that in the limit of large reduced incident energy T of a charged particle, that the ratio of the double to single ionization cross sections at some energy transfer ΔE is equal to the ratio of photoionization cross sections for a photon of energy hν = ΔE, independent of T. He then goes on to find a relationship for this ionization ratio which is not restricted to some specific energy transfer, and shows that the double to single ionization cross section ratio approaches an asymtotic limit for large enough T

First prediction of the direct effect of a confined atom on photoionization of the confining fullerene

International Nuclear Information System (INIS)

McCune, Matthew A; De, Ruma; Chakraborty, Himadri S; Madjet, Mohamed E

2010-01-01

We predict that the confined atom can qualitatively modify the energetic photoionization of some cage levels, even though these levels are of very dominant fullerene character. The effect imposes strong new oscillations in the cross sections which are forbidden to the ionization of empty fullerenes. Results are presented for the AratC 60 endofullerene compound. (fast track communication)

First prediction of the direct effect of a confined atom on photoionization of the confining fullerene

Energy Technology Data Exchange (ETDEWEB)

McCune, Matthew A; De, Ruma; Chakraborty, Himadri S [Center for Innovation and Entrepreneurship, Department of Chemistry and Physics, Northwest Missouri State University, Maryville, MO 64468 (United States); Madjet, Mohamed E, E-mail: himadri@nwmissouri.ed [Institute of Chemistry and Biochemistry, Free University, Fabeckstrasse 36a, D-14195 Berlin (Germany)

2010-09-28

We predict that the confined atom can qualitatively modify the energetic photoionization of some cage levels, even though these levels are of very dominant fullerene character. The effect imposes strong new oscillations in the cross sections which are forbidden to the ionization of empty fullerenes. Results are presented for the AratC{sub 60} endofullerene compound. (fast track communication)

Electron streaking and dissociation in laser-assisted photoionization of molecular hydrogen

International Nuclear Information System (INIS)

Palacios, Alicia; González-Castrillo, Alberto; Martín, Fernando

2014-01-01

We report ab initio calculations on laser-assisted photoionization of the hydrogen molecule in the energy region where autoionization from doubly excited states is expected to occur. We use a UV-pump/IR-probe scheme in which an isolated attosecond UV pulse and a 750 nm IR pulse are combined. The IR pulse has a relatively low intensity (10 12 W cm −2 ), which allows us to perform a perturbative analysis of the calculated ionization probabilities differential in either electron or nuclear energy or both. We show that, for dissociative ionization, the electron energy distributions as a function of time delay exhibit unusual streaking patterns that are due to the presence of autoionizing states. These patterns significantly differ from the standard ones observed in direct single ionization of atoms and molecules. We also show that, by using such a pump–probe scheme, one can suppress autoionization from doubly excited states for time delays between 0 and 4 fs. (paper)

Optical observations on the CRIT-II Critical Ionization Velocity Experiment

International Nuclear Information System (INIS)

Stenbaek-Nielsen, H.C.; Wescott, E.M.; Haerendel, G.; Valenzuela, A.

1990-01-01

A rocket borne Critical Ionization Velocity (CIV) experiment was carried out from Wallops Island at dusk on May 4, 1989. Two barium shaped charges were released below the solar terminator (to prevent photoionization) at altitudes near 400 km. The ambient ionospheric electron density was 5x10 5 cm -3 . The neutral barium jet was directed upwards and at an angle of nominally 45 degrees to B which gives approximately 3x10 23 neutrals with super critical velocity. Ions created by a CIV process in the region of the neutral jet would travel up along B into sunlight where they can be detected optically. Well defined ion clouds (max. brightness 750 R) were observed in both releases. An ionization rate of 0.8%s -1 (125s ionization time constant) can account for the observed ion cloud near the release field line, but the ionization rate falls off with increasing distance from the release. It is concluded that a CIV process was present in the neutral jet out to about 50 km from the release, which is significantly further than allowed by current theories

Binary and Recoil Collisions in Strong Field Double Ionization of Helium

International Nuclear Information System (INIS)

Staudte, A.; Villeneuve, D. M.; Corkum, P. B.; Ruiz, C.; Becker, A.; Schoeffler, M.; Schoessler, S.; Meckel, M.; Doerner, R.; Zeidler, D.; Weber, Th.

2007-01-01

We have investigated the correlated momentum distribution of both electrons from nonsequential double ionization of helium in a 800 nm, 4.5x10 14 W/cm 2 laser field. Using very high resolution coincidence techniques, we find a so-far unobserved fingerlike structure in the correlated electron momentum distribution. The structure can be interpreted as a signature of the microscopic dynamics in the recollision process. We identify features corresponding to the binary and recoil lobe in field-free (e,2e) collisions. This interpretation is supported by analyzing ab initio solutions of a fully correlated three-dimensional helium model

Classical trajectory perspective of atomic ionization in strong laser fields. Semiclassical modeling

International Nuclear Information System (INIS)

Liu, Jie

2014-01-01

Dealing with timely and interesting issues in strong laser physics. Illustrates complex strong field atomic ionization with the simple semiclassical model of classical trajectory perspective for the first time. Provides a theoretical model that can be used to account for recent experiments. The ionization of atoms and molecules in strong laser fields is an active field in modern physics and has versatile applications in such as attosecond physics, X-ray generation, inertial confined fusion (ICF), medical science and so on. Classical Trajectory Perspective of Atomic Ionization in Strong Laser Fields covers the basic concepts in this field and discusses many interesting topics using the semiclassical model of classical trajectory ensemble simulation, which is one of the most successful ionization models and has the advantages of a clear picture, feasible computing and accounting for many exquisite experiments quantitatively. The book also presents many applications of the model in such topics as the single ionization, double ionization, neutral atom acceleration and other timely issues in strong field physics, and delivers useful messages to readers with presenting the classical trajectory perspective on the strong field atomic ionization. The book is intended for graduate students and researchers in the field of laser physics, atom molecule physics and theoretical physics. Dr. Jie Liu is a professor of Institute of Applied Physics and Computational Mathematics, China and Peking University.

Ionization and recombination in attosecond electric field pulses

International Nuclear Information System (INIS)

Dimitrovski, Darko; Solov'ev, Eugene A.; Briggs, John S.

2005-01-01

Based on the results of a previous communication [Dimitrovski et al., Phys. Rev. Lett. 93, 083003 (2004)], we study ionization and excitation of a hydrogenic atom from the ground and first excited states in short electric field pulses of several cycles. A process of ionization and recombination which occurs periodically in time is identified, for both small and extremely large peak electric field strengths. In the limit of large electric peak fields closed-form analytic expressions for the population of the initial state after single- and few-cycle pulses are derived. These formulas, strictly valid for asymptotically large momentum transfer from the field, give excellent agreement with fully numerical calculations for all momentum transfers

Multiple ionization dynamics of molecules in intense laser fields

International Nuclear Information System (INIS)

Ichimura, Atsushi; Ohyama-Yamaguchi, Tomoko

2005-01-01

A classical field-ionization model is developed for sequential multiple ionization of diatomic and linear triatomic molecules exposed to intense (∼ 10 15 W/cm 2 ) laser fields. The distance R ion of Coulomb explosion is calculated for a combination of fragment charges, by considering nonadiabatic excitation followed by field ionization associated with the inner and outer saddle points. For diatomic molecules (N 2 , NO, and I 2 ), the model explains behaviors observed in experiments, as R ion (21→31) ion (21→22) between competing charge-asymmetric and symmetric channels, and even-odd fluctuation along a principal pathway. For a triatomic molecule CO 2 , a comparison of the model with an experiment suggests that charge-symmetric (or nearly symmetric) channels are dominantly populated. (author)

Analysis of anabolic steroids in urine by gas chromatography-microchip atmospheric pressure photoionization-mass spectrometry with chlorobenzene as dopant.

Science.gov (United States)

Hintikka, Laura; Haapala, Markus; Kuuranne, Tiia; Leinonen, Antti; Kostiainen, Risto

2013-10-18

A gas chromatography-microchip atmospheric pressure photoionization-tandem mass spectrometry (GC-μAPPI-MS/MS) method was developed for the analysis of anabolic androgenic steroids in urine as their trimethylsilyl derivatives. The method utilizes a heated nebulizer microchip in atmospheric pressure photoionization mode (μAPPI) with chlorobenzene as dopant, which provides high ionization efficiency by producing abundant radical cations with minimal fragmentation. The performance of GC-μAPPI-MS/MS was evaluated with respect to repeatability, linearity, linear range, and limit of detection (LOD). The results confirmed the potential of the method for doping control analysis of anabolic steroids. Repeatability (RSD<10%), linearity (R(2)≥0.996) and sensitivity (LODs 0.05-0.1ng/mL) were acceptable. Quantitative performance of the method was tested and compared with that of conventional GC-electron ionization-MS, and the results were in good agreement. Copyright © 2013 Elsevier B.V. All rights reserved.

Ionization of atoms by high energy photons

International Nuclear Information System (INIS)

Amusia, M.Y.; Ioffe, A.F.

1994-01-01

Photoionization of atoms by high energy photons is considered. It is emphasized that in this frequency region the cross section and other characteristics of the process are strongly effected by electron shell polarization and rearrangement effects, including that due to inner vacancy Auger decay. In the effects of nuclear structure could be important and noticeable, i.e. of virtual or real excitation of the nucleus degrees of freedom and of the Quantum Electrodynamics vacuum. Ionization accompanied by secondary photon emission (Compton ionization) is analyzed in the considered domain of energies

Parabolic versus spherical partial cross sections for photoionization excitation of He near threshold

International Nuclear Information System (INIS)

Bouri, C.; Selles, P.; Malegat, L.; Kwato Njock, M. G.

2006-01-01

Spherical and parabolic partial cross sections and asymmetry parameters, defined in the ejected electron frame, are presented for photoionization excitation of the helium atom at 0.1 eV above its double ionization threshold. A quantitative law giving the dominant spherical partial wave l dom for each excitation level n is obtained. The parabolic partial cross sections are shown to satisfy the same approximate selection rules as the related Rydberg series of doubly excited states (K,T) n A . The analysis of radial and angular correlations reveals the close relationship between double excitation, ionization excitation, and double ionization. Opposite to a widespread belief, the observed value of the asymmetry parameter is shown to result from the interplay of radial correlations and symmetry constraints, irrespective of angular correlations. Finally, the measurement of parabolic partial cross sections is proposed as a challenge to experimentalists

Selected cis- and trans-3-fluorostyrene rotamers studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

Science.gov (United States)

Wu, Pei Ying; Tzeng, Wen Bih

2015-10-01

We applied two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques to record the vibronic, photoionization efficiency, and cation spectra of the selected rotamers of 3-fluorostyrene. The adiabatic ionization energies of cis- and trans-3-fluorostyrene were determined to be 69 960 ± 5 and 69 856 ± 5 cm-1, respectively. Cation vibrations 10a, 15, 6b, and 12 of both rotamers have been found to have frequencies of 218, 404, 452, and 971 cm-1, respectively. This finding shows that the relative orientation of the vinyl group with respect to the F atom does not affect these vibrations of the 3-fluorostyrene cation. Our one-dimensional potential energy surface calculations support that the cis-trans isomerization of 3-fluorostyrene does not occur under the present experimental conditions.

SDSS-IV MaNGA: identification of active galactic nuclei in optical integral field unit surveys

Science.gov (United States)

Wylezalek, Dominika; Zakamska, Nadia L.; Greene, Jenny E.; Riffel, Rogemar A.; Drory, Niv; Andrews, Brett H.; Merloni, Andrea; Thomas, Daniel

2018-02-01

In this paper, we investigate 2727 galaxies observed by MaNGA as of 2016 June to develop spatially resolved techniques for identifying signatures of active galactic nuclei (AGNs). We identify 303 AGN candidates. The additional spatial dimension imposes challenges in identifying AGNs due to contamination from diffuse ionized gas, extraplanar gas and photoionization by hot stars. We show that the combination of spatially resolved line diagnostic diagrams and additional cuts on H α surface brightness and H α equivalent width can distinguish between AGN-like signatures and high-metallicity galaxies with low-ionization nuclear emission-line regions-like spectra. Low-mass galaxies with high specific star formation rates are particularly difficult to diagnose and routinely show diagnostic line ratios outside of the standard star formation locus. We develop a new diagnostic - the distance from the standard diagnostic line in the line-ratio space - to evaluate the significance of the deviation from the star formation locus. We find 173 galaxies that would not have been selected as AGN candidates based on single-fibre spectral measurements but exhibit photoionization signatures suggestive of AGN activity in the Mapping Nearby Galaxies at APO resolved observations, underscoring the power of large integral field unit surveys. A complete census of these new AGN candidates is necessary to understand their nature and probe the complex co-evolution of supermassive black holes and their hosts.

Channel-closing effects in strong-field ionization by a bicircular field

Science.gov (United States)

Milošević, D. B.; Becker, W.

2018-03-01

Channel-closing effects, such as threshold anomalies and resonantlike intensity-dependent enhancements in strong-field ionization by a bicircular laser field are analyzed. A bicircular field consists of two coplanar corotating or counter-rotating circularly polarized fields having different frequencies. For the total detachment rate of a negative ion by a bicircular field we observe threshold anomalies and explain them using the Wigner threshold law and energy and angular momentum conservation. For the corotating bicircular case, these effects are negligible, while for the counter-rotating case they are pronounced and their position depends on the magnetic quantum number of the initial state. For high-order above-threshold ionization of rare-gas atoms by a counter-rotating bicircular laser field we observe very pronounced intensity-dependent enhancements. We find all four types of threshold anomalies known from collision theory. Contrary to the case of linear polarization, channel-closing effects for a bicircular field are visible also in the cutoff region of the electron energy spectrum, which is explained using quantum-orbit theory.

Integral Field Spectroscopy of the Extended Emission-Line Region of 4C 37.43

Science.gov (United States)

Fu, Hai; Stockton, Alan

2007-09-01

We present Gemini integral field spectroscopy and Keck II long-slit spectroscopy of the extended emission-line region (EELR) around the quasar 4C 37.43. The velocity structure of the ionized gas is complex and cannot be explained globally by a simple dynamical model. The spectra from the clouds are inconsistent with shock or ``shock + precursor'' ionization models, but they are consistent with photoionization by the quasar nucleus. The best-fit photoionization model requires a low-metallicity [12+log(O/H)Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the financial support of the W. M. Keck Foundation.

Optimum conditions for the determination of ionization potentials, appearance potentials and fine structure in ionization efficiency curves using edd technique

International Nuclear Information System (INIS)

Selim, Ezzat T.; El-Kholy, S.B.; Zahran, Nagwa F.

1978-01-01

The optimum conditions for determining ionization potentials as well as fine structure in electron impact ionization efficiency curves are studied using energy distribution difference technique. Applying these conditions to Ar + , Kr + , CO + 2 and N + from N 2 , very good agreement is obtained when compared with results determined by other techniques including UV spectroscopy. The merits and limitation of the technique are also discussed

Collisional ionization of Na by HBr in weak to strong electric fields

International Nuclear Information System (INIS)

Safinya, K.A.; Gallagher, T.F.; Sandner, W.; Gounand, F.

1985-01-01

We report the effect of static electric fields on the collisional ionization of highly excited sodium atoms by HBr. The binding energy dependence of the collisional ionization cross section is measured at zero field and in static electric fields up to that point at which the atom field ionizes. The applied electric field lowers the ionization threshold of the atom from its zero field value. Therefore an atom near the ionization threshold in an electric field is of smaller size than a free field atom with the same binding energy. Thus measuring the binding energy dependence of the cross section at different values of the electric field allows us to study the effects of the physical size of the atom on the cross section. The effect of the electric field was to lower the measured ionization cross section. However, the binding energy dependence of the cross section remains unchanged at the level of our measurement accuracy. The measured cross sections are larger for larger atoms, exhibit a drop with increasing binding energy characteristic of rotational to electronic excitation transfer, and are of order 10 -12 --10 -11 cm 2 . A simple calculation based on dipole (J→ J-1) excitation transfer from the molecule to the atom predicts, with good agreement, the binding energy dependence of the cross section. The electric field dependence of the data however, is not shown in the theory

Electron Correlation in the Ionization Continuum of Molecules: Photoionization of N2 in the Vicinity of the Hopfield Series of Autoionizing States.

Science.gov (United States)

Klinker, Markus; Marante, Carlos; Argenti, Luca; González-Vázquez, Jesús; Martín, Fernando

2018-02-15

Direct measurement of autoionization lifetimes by using time-resolved experimental techniques is a promising approach when energy-resolved spectroscopic methods do not work. Attosecond time-resolved experiments have recently provided the first quantitative determination of autoionization lifetimes of the lowest members of the well-known Hopfield series of resonances in N 2 . In this work, we have used the recently developed XCHEM approach to study photoionization of the N 2 molecule in the vicinity of these resonances. The XCHEM approach allows us to describe electron correlation in the molecular electronic continuum at a level similar to that provided by multireference configuration interaction methods in bound state calculations, a necessary condition to accurately describe autoionization, shakeup, and interchannel couplings occurring in this range of photon energies. Our results show that electron correlation leading to interchannel mixing is the main factor that determines the magnitude and shape of the N 2 photoionization cross sections, as well as the lifetimes of the Hopfield resonances. At variance with recent speculations, nonadiabatic effects do not seem to play a significant role. These conclusions are supported by the very good agreement between the calculated cross sections and those determined in synchrotron radiation and attosecond experiments.

Resonances in electron-molecule scattering and photoionization

International Nuclear Information System (INIS)

Schneider, B.I.; Collins, L.A.

1984-05-01

The development of reliable theoretical models for calculating the decay of quasi-stationary states of molecular systems has become an important endeavor for theoretical chemists. The understanding and analysis of a wide variety of physical and chemical phenomena depend on a knowledge of the behavior of these states in both collisional and photoionization problems. In this article we describe the theory and calculation of these cross sections using our Linear Algebraic/Optical Potential method. The theory makes optimal use of the numerical methods developed to solve large sets of coupled integral equations and the bound state techniques used by quantum chemists. Calculations are presented for a representative class of diatomic and triatomic molecules at varying levels of sophistication and for collisional and photoionization cross sections. 48 references, 11 figures

Photoionization of disk galaxies: An explanation of the sharp edges in the H I distribution

Science.gov (United States)

Dove, James B.; Shull, J. Michael

1994-01-01

We have reproduced the observed radial truncation of the H I distribution in isolated spiral galaxies with a model in which extragalactic radiation photoionizes the gaseous disk. For a galactic mass distribution model that reproduces the observed rotation curves, including dark matter in the disk and halo, the vertical structure of the gas is determined self-consistently. The ionization structure and column densities of H and He ions are computed by solving the radiation transfer equation for both continuum and lines. Our model is similar to that of Maloney, and the H I structure differs by less than 10%. The radial structure of the column density of H I is found to be more sensitive to the extragalactic radiation field than to the distribution of mass. For this reason, considerable progress can be made in determining the extragalactic flux of ionizing photons, phi(sub ex), with more 21 cm observations of isolated galaxies. However, owing to the uncertainty of the radial distribution of total hydrogen at large radii, inferring the extragalactic flux by comparing the observed edges to photoionization models is somewhat subjective. We find 1 x 10(exp 4)/sq cm/s is less than or approximately phi(sub ex) is less than or approximately 5 x 10(exp 4)/sq cm/s, corresponding to 2.1 is less than or approximately iota(sub 0) is less than or approximately 10.5 x 10(exp -23) ergs/sq cm/s/Hz/sr for a 1/nu spectrum. Although somewhat higher, our inferred range of iota(sub 0) is consistent with the large range of values obtained by Kulkarni & Fall from the 'proximity effect' toward Quasi-Stellar Objects (QSOs) at approximately 0.5.

Approaches for the analysis of low molecular weight compounds with laser desorption/ionization techniques and mass spectrometry.

Science.gov (United States)

Bergman, Nina; Shevchenko, Denys; Bergquist, Jonas

2014-01-01

This review summarizes various approaches for the analysis of low molecular weight (LMW) compounds by different laser desorption/ionization mass spectrometry techniques (LDI-MS). It is common to use an agent to assist the ionization, and small molecules are normally difficult to analyze by, e.g., matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) using the common matrices available today, because the latter are generally small organic compounds themselves. This often results in severe suppression of analyte peaks, or interference of the matrix and analyte signals in the low mass region. However, intrinsic properties of several LDI techniques such as high sensitivity, low sample consumption, high tolerance towards salts and solid particles, and rapid analysis have stimulated scientists to develop methods to circumvent matrix-related issues in the analysis of LMW molecules. Recent developments within this field as well as historical considerations and future prospects are presented in this review.

One-photon two-electron processes in helium close to the double ionization threshold

International Nuclear Information System (INIS)

Bouri, C.

2007-04-01

This work presents a study of the 1 P 0 excited states of He that can be reached by absorption of a single photon carrying an energy close to the double ionization threshold (DIT) (79 eV). Above the DIT, these states are the double continuum states; below, they are the double excited states. These two types of states are tightly coupled to the single continuum states with or without excitation of the residual ion He + , owing to their degeneracy in energy. In a one-photon process, these states can only be formed owing to the electronic correlations in the system which must be well described to obtain quantitative good results. Our study is a part of the work which aims at a united description of all these doubly excited, ionized-excited, and double continuum states. We use the Hyperspherical R-Matrix with Semiclassical Outgoing Waves (HRM-SOW) method, initially dedicated to double photoionization studies. We extend it to extract information on the single continuum. This extension allows us to compute cross sections of single photoionization with or without excitation up to n 50 for an excess of 100 meV just above the double ionization threshold. A deep insight into this process is given by a partial waves analysis. The results obtained shed light on the key role of angular and radial correlations. The numerous data we obtain on double and single ionization allow us to establish a continuity relation between these two processes. We show that single ionization with an infinite excitation of the residual ion merges into double photoionization when the excess energy is redistributed between the two electrons. It appears that this relation is valid not only for low but also for high photon energies. Since the HRM-SOW can produce the integrated cross section for double photoionization with high accuracy in the low energy domain, we check the Wannier threshold law. The parameters extracted support strongly this threshold law, and are in good agreement with experimental

Feasibility of gas chromatography-microchip atmospheric pressure photoionization-mass spectrometry in analysis of anabolic steroids.

Science.gov (United States)

Hintikka, Laura; Haapala, Markus; Franssila, Sami; Kuuranne, Tiia; Leinonen, Antti; Kostiainen, Risto

2010-12-24

Mass spectrometers equipped with atmospheric pressure ion sources (API-MS) have been designed to be interfaced with liquid chromatographs (LC) and have rarely been connected to gas chromatographs (GC). Recently, we introduced a heated nebulizer microchip and showed its potential to interface liquid microseparation techniques and GC with API-MS. This study demonstrates the feasibility of GC-microchip atmospheric pressure photoionization-tandem mass spectrometry (GC-μAPPI-MS/MS) in the analysis of underivatized anabolic steroids in urine. The APPI microchip provides high ionization efficiency and produces abundant protonated molecules or molecular ions with minimal fragmentation. The feasibility of GC-μAPPI-MS/MS in the analysis of six selected anabolic steroids in urine samples was studied with respect to intra-batch repeatability, linearity, linear range, and limit of detection (LOD). The method showed good sensitivity (LODs 0.2-1 ng/mL), repeatability (relative standard deviationanabolic steroids. Quantitative performance of the method was tested with two authentic urine samples, and the results were in good agreement with those obtained with conventional GC-electron ionization-MS after derivatization. Copyright © 2010 Elsevier B.V. All rights reserved.

Mass spectrometry. [in organic chemistry

Science.gov (United States)

Burlingame, A. L.; Shackleton, C. H. L.; Howe, I.; Chizhov, O. S.

1978-01-01

A review of mass spectrometry in organic chemistry is given, dealing with advances in instrumentation and computer techniques, selected topics in gas-phase ion chemistry, and applications in such fields as biomedicine, natural-product studies, and environmental pollution analysis. Innovative techniques and instrumentation are discussed, along with chromatographic-mass spectrometric on-line computer techniques, mass spectral interpretation and management techniques, and such topics in gas-phase ion chemistry as electron-impact ionization and decomposition, photoionization, field ionization and desorption, high-pressure mass spectrometry, ion cyclotron resonance, and isomerization reactions of organic ions. Applications of mass spectrometry are examined with respect to bio-oligomers and their constituents, biomedically important substances, microbiology, environmental organic analysis, and organic geochemistry.

Many body perturbation calculations of photoionization

International Nuclear Information System (INIS)

Kelly, H.P.

1979-01-01

The application of many body perturbation theory to the calculation of atomic photoionization cross sections is reviewed. The choice of appropriate potential for the single-particle state is discussed and results are presented for several atoms including resonance structure. In addition to single photoionization, the process of double photoionization is considered and is found to be significant. (Auth.)

Six categories of ionizing radiation quantities practical in various fields

International Nuclear Information System (INIS)

Zheng Junzheng; Zhuo Weihai

2011-01-01

This paper is the part of review on the evolvement of the systems for ionizing radiation quantities and units. In the paper, for better understanding and correct use of the relevant quantities of ionizing radiation, the major ionizing radiation quantities in various fields are divided into six categories. (authors)

Notes on photon assisted field ionization

International Nuclear Information System (INIS)

Niu, B.H.C.; Bryant, P.J.

1979-01-01

A response to comments by Viswanathan et al (2) on a previous publication(1) by the authors is given. It is contended that the original hypothesis of photon assisted field ionization at metal surfaces correctly explains the results reported in Ref. 1

Synchrotron-based valence shell photoionization of CH radical

Energy Technology Data Exchange (ETDEWEB)

Gans, B., E-mail: berenger.gans@u-psud.fr, E-mail: christian.alcaraz@u-psud.fr; Falvo, C. [Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay (France); Holzmeier, F.; Röder, A. [Institut of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg (Germany); Krüger, J.; Garcia, G. A. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint Aubin BP 48, F-91192 Gif sur Yvette Cedex (France); Lopes, A.; Alcaraz, C., E-mail: berenger.gans@u-psud.fr, E-mail: christian.alcaraz@u-psud.fr [Laboratoire de Chimie Physique, UMR 8000 CNRS—Univ. Paris-Sud, Univ. Paris-Saclay, Bât. 350, Centre Universitaire Paris-Sud, F-91405 Orsay Cedex (France); Fittschen, C. [Université Lille, CNRS, UMR 8522–PC2A–Physicochimie des Processus de Combustion et de l’Atmosphère, F-59000 Lille (France); Loison, J.-C. [Institut des Sciences Moléculaires, UMR 5255 CNRS—Université de Bordeaux, Bât. A12, 351 cours de la Libération, F-33405 Talence Cedex (France)

2016-05-28

We report the first experimental observations of X{sup +} {sup 1}Σ{sup +}←X {sup 2}Π and a{sup +} {sup 3}Π←X {sup 2}Π single-photon ionization transitions of the CH radical performed on the DESIRS beamline at the SOLEIL synchrotron facility. The radical was produced by successive hydrogen-atom abstractions on methane by fluorine atoms in a continuous microwave discharge flow tube. Mass-selected ion yields and photoelectron spectra were recorded as a function of photon energy using a double imaging photoelectron/photoion coincidence spectrometer. The ion yield appears to be strongly affected by vibrational and electronic autoionizations, which allow the observation of high Rydberg states of the neutral species. The photoelectron spectra enable the first direct determinations of the adiabatic ionization potential and the energy of the first triplet state of the cation with respect to its singlet ground state. This work also brings valuable information on the complex electronic structure of the CH radical and its cation and adds new observations to complement our understanding of Rydberg states and autoionization processes.

Self-consistent ab initio Calculations for Photoionization and Electron-Ion Recombination Using the R-Matrix Method

Science.gov (United States)

Nahar, S. N.

2003-01-01

Most astrophysical plasmas entail a balance between ionization and recombination. We present new results from a unified method for self-consistent and ab initio calculations for the inverse processes of photoionization and (e + ion) recombination. The treatment for (e + ion) recombination subsumes the non-resonant radiative recombination and the resonant dielectronic recombination processes in a unified scheme (S.N. Nahar and A.K. Pradhan, Phys. Rev. A 49, 1816 (1994);H.L. Zhang, S.N. Nahar, and A.K. Pradhan, J.Phys.B, 32,1459 (1999)). Calculations are carried out using the R-matrix method in the close coupling approximation using an identical wavefunction expansion for both processes to ensure self-consistency. The results for photoionization and recombination cross sections may also be compared with state-of-the-art experiments on synchrotron radiation sources for photoionization, and on heavy ion storage rings for recombination. The new experiments display heretofore unprecedented detail in terms of resonances and background cross sections and thereby calibrate the theoretical data precisely. We find a level of agreement between theory and experiment at about 10% for not only the ground state but also the metastable states. The recent experiments therefore verify the estimated accuracy of the vast amount of photoionization data computed under the OP, IP and related works. features. Present work also reports photoionization cross sections including relativistic effects in the Breit-Pauli R-matrix (BPRM) approximation. Detailed features in the calculated cross sections exhibit the missing resonances due to fine structure. Self-consistent datasets for photoionization and recombination have so far been computed for approximately 45 atoms and ions. These are being reported in a continuing series of publications in Astrophysical J. Supplements (e.g. references below). These data will also be available from the electronic database TIPTOPBASE (http://heasarc.gsfc.nasa.gov)

Photoionization Efficiencies of Five Polycyclic Aromatic Hydrocarbons.

Science.gov (United States)

Johansson, K Olof; Campbell, Matthew F; Elvati, Paolo; Schrader, Paul E; Zádor, Judit; Richards-Henderson, Nicole K; Wilson, Kevin R; Violi, Angela; Michelsen, Hope A

2017-06-15

We have measured photoionization-efficiency curves for pyrene, fluoranthene, chrysene, perylene, and coronene in the photon energy range of 7.5-10.2 eV and derived their photoionization cross-section curves in this energy range. All measurements were performed using tunable vacuum ultraviolet (VUV) radiation generated at the Advanced Light Source synchrotron at Lawrence Berkeley National Laboratory. The VUV radiation was used for photoionization, and detection was performed using a time-of-flight mass spectrometer. We measured the photoionization efficiency of 2,5-dimethylfuran simultaneously with those of pyrene, fluoranthene, chrysene, perylene, and coronene to obtain references of the photon flux during each measurement from the known photoionization cross-section curve of 2,5-dimethylfuran.

Three-dimensional spatial imaging in multiphoton ionization rate measurements

International Nuclear Information System (INIS)

Bredy, Richard; Camp, Howard A.; Nguyen, Hai; Awata, Takaaki; Shan Bing; Chang Zhenghu; DePaola, B.D.

2004-01-01

An experiment is described in which an apparatus is used to demonstrate the feasibility of measuring multiphoton photoionization rates in the interaction of short pulsed lasers with atoms or molecules. With this methodology, the ionization rate is measured as a function of the spatial position in the beam-waist region of the laser through the direct three-dimensional spatial imaging of the ionization events. Thus, if the spatial dependence of the laser beam intensity were known, a series of experiments could yield the intensity dependence of multiphoton ionization without the assumptions or errors that are generally inherent in the integration over one or more dimensions in the laser focal volume

Measurements of excited-state-to-excited-state transition probabilities and photoionization cross-sections using laser-induced fluorescence and photoionization signals

International Nuclear Information System (INIS)

Shah, M.L.; Sahoo, A.C.; Pulhani, A.K.; Gupta, G.P.; Dikshit, B.; Bhatia, M.S.; Suri, B.M.

2014-01-01

Laser-induced photoionization and fluorescence signals were simultaneously observed in atomic samarium using Nd:YAG-pumped dye lasers. Two-color, three-photon photoionization and two-color fluorescence signals were recorded simultaneously as a function of the second-step laser power for two photoionization pathways. The density matrix formalism has been employed to analyze these signals. Two-color laser-induced fluorescence signal depends on the laser powers used for the first and second-step transitions as well as the first and second-step transition probability whereas two-color, three-photon photoionization signal depends on the third-step transition cross-section at the second-step laser wavelength along with the laser powers and transition probability for the first and second-step transitions. Two-color laser-induced fluorescence was used to measure the second-step transition probability. The second-step transition probability obtained was used to infer the photoionization cross-section. Thus, the methodology combining two-color, three-photon photoionization and two-color fluorescence signals in a single experiment has been established for the first time to measure the second-step transition probability as well as the photoionization cross-section. - Highlights: • Laser-induced photoionization and fluorescence signals have been simultaneously observed. • The density matrix formalism has been employed to analyze these signals. • Two-color laser-induced fluorescence was used to measure the second-step transition probability. • The second-step transition probability obtained was used to infer the photoionization cross-section. • Transition probability and photoionization cross-section have been measured in a single experiment

Laser ionization installation for measurement of atomic beam parameters

CERN Document Server

Tukhlibaev, O; Khalilov, E E; Alimov, U Z

2002-01-01

The design of the laser ionization installation for determination of the atomic beam intensity, density and spatial structure is described. The method of the atoms laser resonance staged photoionization is applied in the installation. The above installation consists of two lasers on the dyestuffs, the atomizer, the ionization system and the ion signals registration system. The results of studies on the spatial structure of the In atoms beam are presented. The proposed method provides for the spatial resolution at the level of 10-100 mu m

Density-dependent expressions for photoionization cross-sections

International Nuclear Information System (INIS)

Sun Weiguo; Ma Xiaoguang; Cheng Yansong

2004-01-01

Alternative expressions for photoionization cross-sections and dielectric influence functions are suggested to study the photoionization cross-sections of atoms in solid system. The basic picture is that the photoionization cross-section of atoms in a real system can be described as the coupling between quantum quantity (QQ) and classical quantity (CQ) parts. The QQ part represents the photoionization cross-sections of an isolated particle, while the CQ part may represent most of the important influence of the macroscopic effects (e.g., the interactions of all surrounding polarized particles, and the dielectric property, etc.) on the photoionization cross-sections. The applications to the barium system show that the number-density-dependent new photoionization formula not only obtains the same cross-sections as those from the first order approximation for ideal gas, but also can generate the cross-sections for solid barium by transforming those of ideal gas of the same species using the dielectric influence function

Density-dependent expressions for photoionization cross-sections

Energy Technology Data Exchange (ETDEWEB)

Sun Weiguo; Ma Xiaoguang; Cheng Yansong

2004-06-07

Alternative expressions for photoionization cross-sections and dielectric influence functions are suggested to study the photoionization cross-sections of atoms in solid system. The basic picture is that the photoionization cross-section of atoms in a real system can be described as the coupling between quantum quantity (QQ) and classical quantity (CQ) parts. The QQ part represents the photoionization cross-sections of an isolated particle, while the CQ part may represent most of the important influence of the macroscopic effects (e.g., the interactions of all surrounding polarized particles, and the dielectric property, etc.) on the photoionization cross-sections. The applications to the barium system show that the number-density-dependent new photoionization formula not only obtains the same cross-sections as those from the first order approximation for ideal gas, but also can generate the cross-sections for solid barium by transforming those of ideal gas of the same species using the dielectric influence function.

Indirect double photoionization of water

Science.gov (United States)

Resccigno, T. N.; Sann, H.; Orel, A. E.; Dörner, R.

2011-05-01

The vertical double ionization thresholds of small molecules generally lie above the dissociation limits corresponding to formation of two singly charged fragments. This gives the possibility of populating singly charged molecular ions by photoionization in the Franck-Condon region at energies below the lowest dication state, but above the dissociation limit into two singly charged fragment ions. This process can produce a superexcited neutral fragment that autoionizes at large internuclear separation. We study this process in water, where absorption of a photon produces an inner-shell excited state of H2O+ that fragments to H++OH*. The angular distribution of secondary electrons produced by OH* when it autoionizes produces a characteristic asymmetric pattern that reveals the distance, and therefore the time, at which the decay takes place. LBNL, Berkeley, CA, J. W. Goethe Universität, Frankfurt, Germany. Work performed under auspices of US DOE and supported by OBES, Div. of Chemical Sciences.

Measurements of meteor smoke particles during the ECOMA-2006 campaign: 1. Particle detection by active photoionization

Science.gov (United States)

Rapp, Markus; Strelnikova, Irina

2009-03-01

We present a new design of an in situ detector for the study of meteor smoke particles (MSPs) in the middle atmosphere. This detector combines a classical Faraday cup with a xenon-flashlamp for the active photoionization/photodetachment of MSPs and the subsequent detection of corresponding photoelectrons. This instrument was successfully launched in September 2006 from the Andøya Rocket Range in Northern Norway. A comparison of photocurrents measured during this rocket flight and measurements performed in the laboratory proves that observed signatures are truly due to photoelectrons. In addition, the observed altitude cut-off at 60 km (i.e., no signals were observed below this altitude) is fully understood in terms of the mean free path of the photoelectrons in the ambient atmosphere. This interpretation is also proven by a corresponding laboratory experiment. Consideration of all conceivable species which can be ionized by the photons of the xenon-flashlamp demonstrates that only MSPs can quantitatively explain the measured currents below an altitude of 90 km. Above this altitude, measured photocurrents are most likely due to photoionization of nitric oxide. In conclusion, our results demonstrate that the active photoionization and subsequent detection of photoelectrons provides a promising new tool for the study of MSPs in the middle atmosphere. Importantly, this new technique does not rely on the a priori charge of the particles, neither is the accessible particle size range severely limited by aerodynamical effects. Based on the analysis described in this study, the geophysical interpretation of our measurements is presented in the companion paper by Strelnikova, I., et al. [2008. Measurements of meteor smoke particles during the ECOMA-2006 campaign: 2. results. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.07.011].

X-ray Heating and Electron Temperature of Laboratory Photoionized Plasmas

Science.gov (United States)

Mancini, Roberto; Lockard, Tom; Mayes, Daniel C.; Loisel, Guillaume; Bailey, James E.; Rochau, Gregory; Abdallah, J.; Golovkin, I.

2018-06-01

In separate experiments performed at the Z facility of Sandia National Laboratories two different samples were employed to produce and characterize photoionized plasmas. One was a gas cell filled with neon, and the other was a thin silicon layer coated with plastic. Both samples were driven by the broadband x-ray flux produced at the collapse of a wire array z-pinch implosion. Transmission spectroscopy of a narrowband portion of the x-ray flux was used to diagnose the charge state distribution, and the electron temperature was extracted from a Li-like ion level population ratio. To interpret the temperature measurement, we performed Boltzmann kinetics and radiation-hydrodynamic simulations. We found that non-equilibrium atomic physics and the coupling of the radiation flux to the atomic level population kinetics play a critical role in modeling the x-ray heating of photoionized plasmas. In spite of being driven by similar x-ray drives, differences of ionization and charged state distributions in the neon and silicon plasmas are reflected in the plasma heating and observed electron temperatures.This work was sponsored in part by DOE Office of Science Grant DE-SC0014451, and the Z Facility Fundamental Science Program of SNL.

Atmospheric pressure ionization-tandem mass spectrometry of the phenicol drug family.

Science.gov (United States)

Alechaga, Élida; Moyano, Encarnación; Galceran, M Teresa

2013-11-01

In this work, the mass spectrometry behaviour of the veterinary drug family of phenicols, including chloramphenicol (CAP) and its related compounds thiamphenicol (TAP), florfenicol (FF) and FF amine (FFA), was studied. Several atmospheric pressure ionization sources, electrospray (ESI), atmospheric pressure chemical ionization and atmospheric pressure photoionization were compared. In all atmospheric pressure ionization sources, CAP, TAP and FF were ionized in both positive and negative modes; while for the metabolite FFA, only positive ionization was possible. In general, in positive mode, [M + H](+) dominated the mass spectrum for FFA, while the other compounds, CAP, TAP and FF, with lower proton affinity showed intense adducts with species present in the mobile phase. In negative mode, ESI and atmospheric pressure photoionization showed the deprotonated molecule [M-H](-), while atmospheric pressure chemical ionization provided the radical molecular ion by electron capture. All these ions were characterized by tandem mass spectrometry using the combined information obtained by multistage mass spectrometry and high-resolution mass spectrometry in a quadrupole-Orbitrap instrument. In general, the fragmentation occurred via cyclization and losses or fragmentation of the N-(alkyl)acetamide group, and common fragmentation pathways were established for this family of compounds. A new chemical structure for the product ion at m/z 257 for CAP, on the basis of the MS(3) and MS(4) spectra is proposed. Thermally assisted ESI and selected reaction monitoring are proposed for the determination of these compounds by ultra high-performance liquid chromatography coupled to tandem mass spectrometry, achieving instrumental detection limits down to 0.1 pg. Copyright © 2013 John Wiley & Sons, Ltd.

High-frequency, high-intensity photoionization

Science.gov (United States)

Reiss, H. R.

1996-02-01

Two analytical methods for computing ionization by high-frequency fields are compared. Predicted ionization rates compare well, but energy predictions for the onset of ionization differ radically. The difference is shown to arise from the use of a transformation in one of the methods that alters the zero from which energy is measured. This alteration leads to an apparent energy threshold for ionization that can, especially in the stabilization regime, differ strongly from the laboratory measurement. It is concluded that channel closings in intense-field ionization can occur at high as well as low frequencies. It is also found that the stabilization phenomenon at high frequencies, very prominent for hydrogen, is absent in a short-range potential.

Double electron ionization in Compton scattering of high energy photons by helium atoms

International Nuclear Information System (INIS)

Amusia, M.Y.; Mikhailov, A.I.

1995-01-01

The cross section for double-electron ionization of two-electron atoms and ions in Compton scattering of high energy photons is calculated. It is demonstrated that its dependence on the incoming photon frequency is the same as that for single-electron ionization. The ratio of open-quotes double-to-singleclose quotes ionization in Compton scattering was found to be energy independent and almost identical with the corresponding value for photoionization. For the He atom it is 1.68%. This surprising result deserves experimental verification

Double electron ionization in Compton scattering of high energy photons by helium atoms

Energy Technology Data Exchange (ETDEWEB)

Amusia, M.Y.; Mikhailov, A.I. [St. Petersburg Nuclear Physics Institute, Gatchina (Russian Federation)

1995-08-01

The cross section for double-electron ionization of two-electron atoms and ions in Compton scattering of high energy photons is calculated. It is demonstrated that its dependence on the incoming photon frequency is the same as that for single-electron ionization. The ratio of {open_quotes}double-to-single{close_quotes} ionization in Compton scattering was found to be energy independent and almost identical with the corresponding value for photoionization. For the He atom it is 1.68%. This surprising result deserves experimental verification.

Time-Dependent Photoionization of Gaseous Nebulae: The Pure Hydrogen Case

Science.gov (United States)

Garcia, J.; Elhoussieny, E. E.; Bautista, M. A.; Kallman, Timothy R.

2013-01-01

We study the problem of time-dependent photoionization of low density gaseous nebulae subjected to sudden changes in the intensity of ionizing radiation. To this end, we write a computer code that solves the full timedependent energy balance, ionization balance, and radiation transfer equations in a self-consistent fashion for a simplified pure hydrogen case. It is shown that changes in the ionizing radiation yield ionizationthermal fronts that propagate through the cloud, but the propagation times and response times to such fronts vary widely and nonlinearly from the illuminated face of the cloud to the ionization front (IF). IFthermal fronts are often supersonic, and in slabs initially in pressure equilibrium such fronts yield large pressure imbalances that are likely to produce important dynamical effects in the cloud. Further, we studied the case of periodic variations in the ionizing flux. It is found that the physical conditions of the plasma have complex behaviors that differ from any steady-state solution. Moreover, even the time average of ionization and temperature is different from any steady-state case. This time average is characterized by overionization and a broader IF with respect to the steady-state solution for a mean value of the radiation flux. Around the time average of physical conditions there is a large dispersion in instantaneous conditions, particularly across the IF, which increases with the period of radiation flux variations. Moreover, the variations in physical conditions are asynchronous along the slab due to the combination of nonlinear propagation times for thermal frontsIFs and equilibration times.

Measurements of photoionization cross sections from the 4p, 5d and 7s excited states of potassium

International Nuclear Information System (INIS)

Amin, Nasir; Mahmood, S.; Haq, S.U.; Kalyar, M.A.; Rafiq, M.; Baig, M.A.

2008-01-01

New measurements of the photoionization cross sections from the 4p 2 P 1/2,3/2 , 5d 2 D 5/2,3/2 and 7s 2 S 1/2 excited states of potassium are presented. The cross sections have been measured by two-step excitation and ionization using a Nd:YAG laser in conjunction with a thermionic diode ion detector. By applying the saturation technique, the absolute values of the cross sections from the 4p 2 P 3/2 and 4p 2 P 1/2 states at 355 nm are determined as 7.2±1.1 and 5.6±0.8 Mb, respectively. The photoionization cross section from the 5d 2 D 5/2,3/2 excited state has been measured using two excitation paths, two-step excitation and two-photon excitation from the ground state. The measured values of the cross sections from the 5d 2 D 5/2 state by two-photon excitation from the ground state is 28.9±4.3 Mb, whereas in the two-step excitation, the cross section from the 5d 2 D 3/2 state via the 4p 2 P 1/2 state and from the 5d 2 D 5/2,3/2 states via the 4p 2 P 3/2 state are determined as 25.1±3.8 and 30.2±4.5 Mb, respectively. Besides, we have measured the photoionization cross sections from the 7s 2 S 1/2 excited state using the two-photon excitation from the ground state as 0.61±0.09 Mb

Photoionization of the Buckminsterfullerene Cation.

Science.gov (United States)

Douix, Suzie; Duflot, Denis; Cubaynes, Denis; Bizau, Jean-Marc; Giuliani, Alexandre

2017-01-05

Photoionization of a buckminsterfullerene ion is investigated using an ion trap and a merged beam setup coupled to synchrotron radiation beamlines and compared to theoretical calculations. Absolute measurements derived from the ion trap experiment allow discrepancies concerning the photoionization cross section of C 60 + to be solved.

Historical survey of resonance ionization spectroscopy

International Nuclear Information System (INIS)

Hurst, G.S.

1984-04-01

We have recently celebrated the 10th birthday of Resonance Ionization Spectroscopy (RIS), and this seems an appropriate time to review the history of its development. Basically, RIS is a photophysics process in which tunable light sources are used to remove a valence electron from an atom of selected atomic number, Z. If appropriate lasers are used as the light source, one electron can be removed from each atom of the selected Z in the laser pulse. This implies that RIS can be a very efficient, as well as selective, ionization process. In what we normally call RIS, laser schemes are employed which preserve both of these features. In contrast, multiphoton ionization (MPI) is more general, although not necessarily Z selective or very efficient because resonances are often not used. Early research completed in the USSR and described as selective two-step photoionization, employed resonances to ionize the rubidium atom and served to guide work on laser isotope separation. 29 references, 8 figures

Rotational distributions of molecular photoions following resonant excitation

International Nuclear Information System (INIS)

Poliakoff, E.D.; Chan, J.C.K.; White, M.G.

1986-01-01

We demonstrate that the photoelectron energy mediates the rotational energy distribution of N + 2 ions created by photoionization, and conversely, that rotational energy determinations probe resonant excitation in molecular photoionization. Experimentally, this is accomplished by monitoring the dispersed fluorescence from N + 2 (B 2 Σ + /sub u/) photoions to determine their rotational energy distribution. These results demonstrate that while dipole selection rules constrain the total angular momentum of the electron--ion complex, the partitioning of angular momentum between the photoelectron and photoion depends on the photoejection dynamics. Implications for photoionization and electron impact ionizatin studies are discussed

Inner-shell ionization of atoms by electron, positron and photon impacts

International Nuclear Information System (INIS)

Khare, S.P.; Sinha, P.; Wadehra, J.M.

1994-01-01

Plane wave Born approximation with Coulomb, relativistic and exchange corrections is employed to obtain L1-, L2- and L3-subshell ionization cross sections of several atoms due to electron and positron impacts for projectile energy varying from the threshold of ionization to 60 times the threshold energy. Photoionization cross sections for all the three L-subshells of the atoms are also calculated using the hydrogenic approximation for the atomic wave functions. For L3-subshell the present cross sections due to electron impact are in good agreement with a number of experimental data for different atoms over the entire energy range investigated. For L1- and L2-subshells the present calculations yield qualitative agreement with the experimental data. The agreement between the present results and the limited experimental data for positron impact is also satisfactory. The hydrogenic approximation for the L-subshell photoionization is found to be good at small photon energies but it underestimates the cross sections at large photon energies. (orig.)

Characterization of high-energy photoionization in terms of the singularities of the atomic potential. I. Photoionization of the ground state of a two-electron atom

International Nuclear Information System (INIS)

Suric, T.; Drukarev, E.G.; Pratt, R.H.

2003-01-01

We describe single and double photoionization of two-electron atoms by photoabsorption at high incident photon energies ω (but still ω 2 ) using a unified approach based on asymptotic Fourier transform (AFT) theory modified by Coulombic interactions. Within this approach the matrix elements for photoabsorption processes at high energies can be understood in terms of the singularities of the many-body Coulomb potential. These singularities (e-e and e-N) result in the singularities of the wave functions and the singularities of the e-γ interaction, which determine the asymptotic behavior of the matrix element. Within our unified approach we explain the dominant contributions, including both the dominant contributions to the total cross section for single ionization and for ionization with excitation, and the dominant contributions to the double ionization spectrum, as a Fourier transform asymptotic in a single large momentum (dependent on the process and the region of the spectrum). These dominant contributions are connected, through AFT, with either the e-N singularity or the e-e singularity. The AFT results are modified by Coulombic interactions. We include these modifications, for the cases of single ionization and of double ionization in the shake-off region at high energies, and extract a slowly convergent factor (Stobbe factor). In this way we obtain rapid convergence of the cross sections to their high-energy behaviors. This also allows us to discuss the convergence of ratios of cross sections

Photoelectron photoion molecular beam spectroscopy

International Nuclear Information System (INIS)

Trevor, D.J.

1980-12-01

The use of supersonic molecular beams in photoionization mass spectroscopy and photoelectron spectroscopy to assist in the understanding of photoexcitation in the vacuum ultraviolet is described. Rotational relaxation and condensation due to supersonic expansion were shown to offer new possibilities for molecular photoionization studies. Molecular beam photoionization mass spectroscopy has been extended above 21 eV photon energy by the use of Stanford Synchrotron Radiation Laboratory (SSRL) facilities. Design considerations are discussed that have advanced the state-of-the-art in high resolution vuv photoelectron spectroscopy. To extend gas-phase studies to 160 eV photon energy, a windowless vuv-xuv beam line design is proposed

Inner-shell photoionization and core-hole decay of Xe and XeF2.

Science.gov (United States)

Southworth, Stephen H; Wehlitz, Ralf; Picón, Antonio; Lehmann, C Stefan; Cheng, Lan; Stanton, John F

2015-06-14

Photoionization cross sections and partial ion yields of Xe and XeF2 from Xe 3d(5/2), Xe 3d(3/2), and F 1s subshells in the 660-740 eV range are compared to explore effects of the F ligands. The Xe 3d-ϵf continuum shape resonances dominate the photoionization cross sections of both the atom and molecule, but prominent resonances appear in the XeF2 cross section due to nominal excitation of Xe 3d and F 1s electrons to the lowest unoccupied molecular orbital (LUMO), a delocalized anti-bonding MO. Comparisons of the ion products from the atom and molecule following Xe 3d photoionization show that the charge-state distribution of Xe ions is shifted to lower charge states in the molecule along with production of energetic F(+) and F(2+) ions. This suggests that, in decay of a Xe 3d core hole, charge is redistributed to the F ligands and the system dissociates due to Coulomb repulsion. The ion products from excitation of the F 1s-LUMO resonance are different and show strong increases in the yields of Xe(+) and F(+) ions. The subshell ionization thresholds, the LUMO resonance energies, and their oscillator strengths are calculated by relativistic coupled-cluster methods and agree well with measurements.

Laboratory studies of photoionized plasma related to astrophysics

International Nuclear Information System (INIS)

Yang Peiqiang; Wang Feilu; Zhao Gang

2011-01-01

Photoionized plasma is universal in astronomy and has great importance on account of its close relation to compact astrophysical objects such as black holes. Recently, with the development of high energy density lasers and Z-pinch facilities, it has become possible to simulate astronomical photoionized plasma in the laboratory. These experiments help us to benchmark and modify the photoionization models, and to understand the photoionization processes to diagnose related astronomical plasma environments. (authors)

VUV photo-processing of PAH cations: quantitative study on the ionization versus fragmentation processes.

Science.gov (United States)

Zhen, Junfeng; Castillo, Sarah Rodriguez; Joblin, Christine; Mulas, Giacomo; Sabbah, Hassan; Giuliani, Alexandre; Nahon, Laurent; Martin, Serge; Champeaux, Jean-Philippe; Mayer, Paul M

2016-05-10

Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7 - 20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below ~13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies, all species behave similarly, the ionization yield gradually increases, leveling off between 0.8 and 0.9 at ~18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section, but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them, all are in good agreement with theoretical ones confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models.

VUV PHOTO-PROCESSING OF PAH CATIONS: QUANTITATIVE STUDY ON THE IONIZATION VERSUS FRAGMENTATION PROCESSES

Energy Technology Data Exchange (ETDEWEB)

Zhen, Junfeng; Castillo, Sarah Rodriguez; Joblin, Christine; Mulas, Giacomo; Sabbah, Hassan [Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie, Toulouse (France); Giuliani, Alexandre; Nahon, Laurent [Synchrotron SOLEIL, LOrme des Merisiers, F-91192 Gif sur Yvette Cedex (France); Martin, Serge [Institut Lumière Matière, Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne cedex (France); Champeaux, Jean-Philippe [Laboratoire Collisions Agrégats Réactivité, Université de Toulouse, UPS-IRSAMC, CNRS, 118 Route de Narbonne, Bat 3R1B4, F-31062 Toulouse Cedex 9 (France); Mayer, Paul M., E-mail: christine.joblin@irap.omp.eu [Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa K1N 6N5 (Canada)

2016-05-10

Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7–20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below ∼13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies all species behave similarly; the ionization yield gradually increases, leveling off between 0.8 and 0.9 at ∼18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them; all are in good agreement with theoretical ones, confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models.

VUV PHOTO-PROCESSING OF PAH CATIONS: QUANTITATIVE STUDY ON THE IONIZATION VERSUS FRAGMENTATION PROCESSES

International Nuclear Information System (INIS)

Zhen, Junfeng; Castillo, Sarah Rodriguez; Joblin, Christine; Mulas, Giacomo; Sabbah, Hassan; Giuliani, Alexandre; Nahon, Laurent; Martin, Serge; Champeaux, Jean-Philippe; Mayer, Paul M.

2016-01-01

Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7–20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below ∼13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies all species behave similarly; the ionization yield gradually increases, leveling off between 0.8 and 0.9 at ∼18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them; all are in good agreement with theoretical ones, confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models.

VUV photo-processing of PAH cations: quantitative study on the ionization versus fragmentation processes

Science.gov (United States)

Zhen, Junfeng; Castillo, Sarah Rodriguez; Joblin, Christine; Mulas, Giacomo; Sabbah, Hassan; Giuliani, Alexandre; Nahon, Laurent; Martin, Serge; Champeaux, Jean-Philippe; Mayer, Paul M.

2016-01-01

Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7 – 20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below ~13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies, all species behave similarly, the ionization yield gradually increases, leveling off between 0.8 and 0.9 at ~18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section, but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them, all are in good agreement with theoretical ones confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models. PMID:27212712

Identifying the Tunneling Site in Strong-Field Ionization of H_{2}^{+}.

Science.gov (United States)

Liu, Kunlong; Barth, Ingo

2017-12-15

The tunneling site of the electron in a molecule exposed to a strong laser field determines the initial position of the ionizing electron and, as a result, has a large impact on the subsequent ultrafast electron dynamics on the polyatomic Coulomb potential. Here, the tunneling site of the electron of H_{2}^{+} ionized by a strong circularly polarized (CP) laser pulse is studied by numerically solving the time-dependent Schrödinger equation. We show that the electron removed from the down-field site is directly driven away by the CP field and the lateral photoelectron momentum distribution (LPMD) exhibits a Gaussian-like distribution, whereas the corresponding LPMD of the electron removed from the up-field site differs from the Gaussian shape due to the Coulomb focusing and scattering by the down-field core. Our current study presents the direct evidence clarifying a long-standing controversy over the tunneling site in H_{2}^{+} and raises the important role of the tunneling site in strong-field molecular ionization.

Hole dynamics and spin currents after ionization in strong circularly polarized laser fields

International Nuclear Information System (INIS)

Barth, Ingo; Smirnova, Olga

2014-01-01

We apply the time-dependent analytical R-matrix theory to develop a movie of hole motion in a Kr atom upon ionization by strong circularly polarized field. We find rich hole dynamics, ranging from rotation to swinging motion. The motion of the hole depends on the final energy and the spin of the photoelectron and can be controlled by the laser frequency and intensity. Crucially, hole rotation is a purely non-adiabatic effect, completely missing in the framework of quasistatic (adiabatic) tunneling theories. We explore the possibility to use hole rotation as a clock for measuring ionization time. Analyzing the relationship between the relative phases in different ionization channels we show that in the case of short-range electron-core interaction the hole is always initially aligned along the instantaneous direction of the laser field, signifying zero delays in ionization. Finally, we show that strong-field ionization in circular fields creates spin currents (i.e. different flow of spin-up and spin-down density in space) in the ions. This phenomenon is intimately related to the production of spin-polarized electrons in strong laser fields Barth and Smirnova (2013 Phys. Rev. A 88 013401). We demonstrate that rich spin dynamics of electrons and holes produced during strong field ionization can occur in typical experimental conditions and does not require relativistic intensities or strong magnetic fields. (paper)

A merged-beam setup at SOLEIL dedicated to photoelectron–photoion coincidence studies on ionic species

Energy Technology Data Exchange (ETDEWEB)

Bizau, J.M., E-mail: jean-marc.bizau@u-psud.fr [Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris Paris-Sud, Université Paris-Saclay, F-91405 Orsay (France); Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex (France); Cubaynes, D. [Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris Paris-Sud, Université Paris-Saclay, F-91405 Orsay (France); Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex (France); Guilbaud, S.; El Eassan, N.; Al Shorman, M.M.; Bouisset, E.; Guigand, J.; Moustier, O.; Marié, A.; Nadal, E. [Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris Paris-Sud, Université Paris-Saclay, F-91405 Orsay (France); Robert, E.; Nicolas, C. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex (France); Miron, C. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex (France); Extreme Light Infrastructure—Nuclear Physics, “Horia Hulubei” National Institute for Physics and Nuclear Engineering, 30 Reactorului Street, RO-077125 Măgurele, Jud. Ilfov (Romania)

2016-07-15

Highlights: • Description of a merged-beam setup at SOLEIL synchrotron radiation facility. • Unique setup of this kind allowing photoelectron spectroscopy on ionic species. • Use of electron-ion coincidence to reduce the background. • Examples on the photoionization of Xe{sup 5+} multiply-charged ion. - Abstract: We describe the merged-beam setup permanently installed on a dedicated optical branch of the PLEIADES beamline at SOLEIL, the French synchrotron radiation facility in St-Aubin, delivering photons in the 10–1000 eV photon energy range. The setup is designed both for photoion and photoelectron spectroscopy experiments on atomic and molecular ions. Ion spectrometry is dedicated to the determination of absolute single and multiple photoionization cross sections. Electron spectroscopy brings additional information on the non-radiative decay of inner-vacancies produced in the photoionization processes and allows for the determination of partial cross sections. Efficient reduction of the background in the electron spectra is achieved by the use of the electron-ion coincidence technique. Examples of photoion and photoelectron spectra are given for the Xe{sup 5+} ion.

Near-threshold photoionization of hydrogenlike uranium studied in ion-atom collisions via the time-reversed process.

Science.gov (United States)

Stöhlker, T; Ma, X; Ludziejewski, T; Beyer, H F; Bosch, F; Brinzanescu, O; Dunford, R W; Eichler, J; Hagmann, S; Ichihara, A; Kozhuharov, C; Krämer, A; Liesen, D; Mokler, P H; Stachura, Z; Swiat, P; Warczak, A

2001-02-05

Radiative electron capture, the time-reversed photoionization process occurring in ion-atom collisions, provides presently the only access to photoionization studies for very highly charged ions. By applying the deceleration mode of the ESR storage ring, we studied this process in low-energy collisions of bare uranium ions with low- Z target atoms. This technique allows us to extend the current information about photoionization to much lower energies than those accessible for neutral heavy elements in the direct reaction channel. The results prove that for high- Z systems, higher-order multipole contributions and magnetic corrections persist even at energies close to the threshold.

First light on 3d photoionization of multiply charged xenon ions: a new photon-ion merged beam setup at PETRA III

International Nuclear Information System (INIS)

Ricz, S; Schippers, S; Buhr, T; Holste, K; Jr, A Borovik; Hellhund, J; Schäfer, H-J; Schury, D; Klumpp, S; Mertens, K; Martins, M; Flesch, R; Ulrich, G; Rühl, E; Lower, J; Jahnke, T; Metz, D; Schmidt, L; Schöffler, M; Williams, J B

2014-01-01

A photon-ion merged beam endstation has been set up at the variable polarization XUV-beamline P04 of PETRA III in Hamburg. In a commissioning experiment first results could be obtained for multiple photoionization of Xe q+ ions (q = 1,2,..,5) at photon energies around the 3d ionization threshold.

Schwinger variational principle applied to molecular photoionization

International Nuclear Information System (INIS)

Smith, M.E.

1985-01-01

A method based upon the Schwinger variational principle was developed to study molecular photoionization and electron-molecule scattering. Exact static-exchange solutions to the equations for the continuum orbitals are obtained within the Hartree-Fock approximation; and from these cross sections and angular distributions are derived for both of the above processes. This method was applied to photoionization of the valence levels of three different systems. The first application of this method is a study of the photoionization of the valence levels of NO. Next, vibrationally resolved branching ratios and vibrational state-specific asymmetry parameters for photoionization of the 5sigma level of CO are presented. Finally, a study of the photoionization of the 5sigma level of CO absorbed on a nickel surface is reported. Approximating this system by the linear triatomic molecule NiCO leads to cross sections and angular distributions which are in good agreement with experimental data

Liquid chromatography/mass spectrometric determination of patulin in apple juice using atmospheric pressure photoionization.

Science.gov (United States)

Takino, Masahiko; Daishima, Shigeki; Nakahara, Taketoshi

2003-01-01

This paper describes a comparison between atmospheric pressure chemical ionization (APCI) and the recently introduced atmospheric pressure photoionization (APPI) technique for the liquid chromatography/mass spectrometric (LC/MS) determination of patulin in clear apple juice. A column switching technique for on-line extraction of clear apple juice was developed. The parameters investigated for the optimization of APPI were the ion source parameters fragmentor voltage, capillary voltage, and vaporizer temperature, and also mobile phase composition and flow rate. Furthermore, chemical noise and signal suppression of analyte signals due to sample matrix interference were investigated for both APCI and APPI. The results indicated that APPI provides lower chemical noise and signal suppression in comparison with APCI. The linear range for patulin in apple juice (correlation coefficient >0.999) was 0.2-100 ng mL(-1). Mean recoveries of patulin in three apple juices ranged from 94.5 to 103.2%, and the limit of detection (S/N = 3), repeatability and reproducibility were 1.03-1.50 ng mL(-1), 3.9-5.1% and 7.3-8.2%, respectively. The total analysis time was 10.0 min. Copyright 2003 John Wiley & Sons, Ltd.

Improving the accuracy of ionization chamber dosimetry in small megavoltage x-ray fields

Science.gov (United States)

McNiven, Andrea L.

computed tomography dose index (CTDI), a concept normally used in diagnostic radiology. This involved experimental determination of the fan beam thickness using the ion chambers to acquire fan beam profiles and extrapolation to a 'zero-size' detector. In conclusion, improvements have been made in the accuracy of small field dosimetry measurements in stereotactic radiotherapy and helical tomotherapy. This was completed through introduction of an original technique involving micro-CT imaging for sensitive volume determination and potentially ion chamber calibration coefficients, the use of appropriate Monte Carlo derived correction factors for RDF measurement, and the exploitation of the partial volume effect for helical tomotherapy fan beam dosimetry. With improved dosimetry for a wide range of challenging small x-ray field situations, it is expected that the patient's radiation safety will be maintained, and that clinical trials will adopt calibration protocols specialized for modern radiotherapy with small fields or beamlets. Keywords. radiation therapy, ionization chambers, small field dosimetry, stereotactic radiotherapy, helical tomotherapy, micro-CT.

Multiphoton atomic ionization in the field of a very short laser pulse

International Nuclear Information System (INIS)

Popov, V.S.

2001-01-01

Closed analytic expressions are derived for the probability of multiphoton atomic and ionic ionization in a variable electric field E(t), which are applicable for arbitrary Keldysh parameters γ. Dependencies of the ionization probability and photoelectron pulse spectrum on the shape of a very short laser pulse are analyzed. Examples of pulse fields of various forms, including a modulated light pulse with a Gaussian or Lorentz envelope, are considered in detail. The interference effect in the photoelectron energy spectrum during atomic ionization by a periodic field of a general form is examined. The range of applicability of the adiabatic approximation in the multiphoton ionization theory is discussed. The imaginary time method is used in the calculations, which allows the probability of particle tunneling through oscillating barriers to be effectively calculated

Three-colour photoionization optogalvanic spectroscopy in U-Ne hollow cathode discharges: observation of even-parity autoionization states of uranium

International Nuclear Information System (INIS)

Mandal, P.K.; Seema, A.U.; Das, R.C.; Shah, M.L.; Dev, Vas; Suri, B.M.

2013-01-01

Three-colour three-step photoionization spectroscopy of uranium has been performed in a U-Ne hollow cathode discharge tube by temporally resolving three-colour photoionization optogalvanic (PIOG) signal from the normal optogalvanic (OG) signal using three tunable pulsed dye lasers. U-Ne hollow cathode discharge tube has been used as a source of uranium atomic vapour and photoionization detector. Using this technique, photoionization spectra of uranium have been investigated systematically in the energy region 52150-52590 cm -1 , through three different excitation pathways, originating from its ground state, 0 cm -1 ( 5 L 0 6 ). By analyzing the three-colour photoionization spectra sixty new even-parity autoionization resonances of uranium have been identified and their probable total angular momentum (J) values have been assigned according to the J-momentum selection rule. (author)

Initial ionization stage of FRC formation

International Nuclear Information System (INIS)

Commisso, R.J.; Armstrong, W.T.; Cochrane, J.C.; Ekdahl, C.A.; Lipson, J.; Linford, R.K.; Sherwood, E.G.; Siemon, R.E.; Tuszewski, M.

1980-01-01

A Field-Reversed Configuration (FRC) is a prolate compact torus that is confined by poloidal fields only. Theta-pinch formation of an FRC employs an initial bias field, B 1 , whose direction is opposite to that of the main theta-pinch field. Some fraction of the flux associated with this bias field eventually constitutes the closed-field-line flux of the FRC. Experimental and theoretical evidence suggest that the longest-lived FRC's are obtained when the closed flux is maximized. Because the initial ionization is done in the presence of the bias field, the actual bias flux available at the time of application of the main theta-pinch field depends strongly on the initial ionization, or preionization, technique used. In this paper we report on experiments characterizing the previously used theta-pinch preionization technique that employed a net field (bias plus preionization) null, or zero-crossing, of the axial component of the magnetic field to break down the gas. We also discuss results of experiments designed to develop preionization techniques in which the gas breakdown is not accomplished by a zero-crossing

Improving the Selectivity of the ISOLDE Resonance Ionization Laser Ion Source and In-Source Laser Spectroscopy of Polonium

CERN Document Server

Fink, Daniel Andreas; Jochim, Selim

Exotic atomic nuclei far away from stability are fascinating objects to be studied in many scientic elds such as atomic-, nuclear-, and astrophysics. Since these are often short-lived isotopes, it is necessary to couple their production with immediate extraction and delivery to an experiment. This is the purpose of the on-line isotope separator facility, ISOLDE, at CERN. An essential aspect of this laboratory is the Resonance Ionization Laser Ion Source (RILIS) because it provides a fast and highly selective means of ionizing the reaction products. This technique is also a sensitive laser-spectroscopy tool for the development and improvement of electron excitation schemes for the resonant laser photoionization and the study of the nuclear structure or fundamental atomic physics. Each of these aspects of the RILIS applications are subjects of this thesis work: a new device for the suppression of unwanted surface ionized contaminants in RILIS ion beams, known as the Laser Ion Source and Trap (LIST), was impleme...

Dual ring multilayer ionization chamber and theory-based correction technique for scanning proton therapy.

Science.gov (United States)

Takayanagi, Taisuke; Nihongi, Hideaki; Nishiuchi, Hideaki; Tadokoro, Masahiro; Ito, Yuki; Nakashima, Chihiro; Fujitaka, Shinichiro; Umezawa, Masumi; Matsuda, Koji; Sakae, Takeji; Terunuma, Toshiyuki

2016-07-01

To develop a multilayer ionization chamber (MLIC) and a correction technique that suppresses differences between the MLIC and water phantom measurements in order to achieve fast and accurate depth dose measurements in pencil beam scanning proton therapy. The authors distinguish between a calibration procedure and an additional correction: 1-the calibration for variations in the air gap thickness and the electrometer gains is addressed without involving measurements in water; 2-the correction is addressed to suppress the difference between depth dose profiles in water and in the MLIC materials due to the nuclear interaction cross sections by a semiempirical model tuned by using measurements in water. In the correction technique, raw MLIC data are obtained for each energy layer and integrated after multiplying them by the correction factor because the correction factor depends on incident energy. The MLIC described here has been designed especially for pencil beam scanning proton therapy. This MLIC is called a dual ring multilayer ionization chamber (DRMLIC). The shape of the electrodes allows the DRMLIC to measure both the percentage depth dose (PDD) and integrated depth dose (IDD) because ionization electrons are collected from inner and outer air gaps independently. IDDs for which the beam energies were 71.6, 120.6, 159, 180.6, and 221.4 MeV were measured and compared with water phantom results. Furthermore, the measured PDDs along the central axis of the proton field with a nominal field size of 10 × 10 cm(2) were compared. The spread out Bragg peak was 20 cm for fields with a range of 30.6 and 3 cm for fields with a range of 6.9 cm. The IDDs measured with the DRMLIC using the correction technique were consistent with those that of the water phantom; except for the beam energy of 71.6 MeV, all of the points satisfied the 1% dose/1 mm distance to agreement criterion of the gamma index. The 71.6 MeV depth dose profile showed slight differences in the shallow

Photoionization of H2O at high resolution

International Nuclear Information System (INIS)

Dehmer, P.M.; Chupka, W.A.

1978-01-01

The relative photoionization cross sections for the formation of H 2 O + , OH + , and H + from H 2 O were measured at high wavelength resolution using a 3-meter photoionization mass spectrometer equipped with a quadrupole mass flter and a 1-meter photoionization mass spectrometer equipped with a 12-inch radius, 60 0 sector magnetic mass spectrometer. Discrete structure in the parent ion photoionization efficiency curve is interpreted in terms of Rydberg series converging to excited states of the H 2 O + ion. 9 references

Ionizing and non-ionizing radiation and the risk of childhood cancer-illustrated with domestic radon and radio frequency electromagnetic field exposure

OpenAIRE

Hauri, Dimitri

2013-01-01

Background Children are exposed to many different environmental factors, including exposure to low-dose ionizing radiation and to non-ionizing radiation. Low-dose ionizing radiation comprises anthropogenic modified radiation and natural ionizing radiation from cosmic rays from the atmosphere, terrestrial gamma radiation from radionuclides in rocks and soils and radiation from radon. Non-ionizing radiation comprises optical radiation and radiation from electromagnetic fields. The la...

Tunneling ionization and harmonic generation in two-color fields

International Nuclear Information System (INIS)

Kondo, K.; Kobayashi, Y.; Sagisaka, A.; Nabekawa, Y.; Watanabe, S.

1996-01-01

Tunneling ionization and harmonic generation in two-color fields were studied with a fundamental beam (ω) and its harmonics (2ω,3ω), which were generated by a 100-fs Ti:sapphire laser. Ion yields of atoms and molecules were successfully controlled by means of a change in the relative phase between ω and 3ω pulses. Two-color interference was clearly observed in photoelectron spectra and harmonic spectra. In the ω endash 2ω field even-order harmonics were observed in which the intensity was almost equal to that of the odd harmonics because of an asymmetric optical field. These results were compared with the quasi-static model for ionization and with the quantum theory for harmonic generation. copyright 1996 Optical Society of America

Dosimetry of ionizing radiation

International Nuclear Information System (INIS)

Musilek, L.; Seda, J.; Trousil, J.

1992-01-01

The publication deals with a major field of ionizing radiation dosimetry, viz., integrating dosimetric methods, which are the basic means of operative dose determination. It is divided into the following sections: physical and chemical effects of ionizing radiation; integrating dosimetric methods for low radiation doses (film dosimetry, nuclear emulsions, thermoluminescence, radiophotoluminescence, solid-state track detectors, integrating ionization dosemeters); dosimetry of high ionizing radiation doses (chemical dosimetric methods, dosemeters based on the coloring effect, activation detectors); additional methods applicable to integrating dosimetry (exoelectron emission, electron spin resonance, lyoluminescence, etc.); and calibration techniques for dosimetric instrumentation. (Z.S.). 422 refs

Multiphoton ionization of (Xe)n and (NO)n clusters using a picosecond laser

International Nuclear Information System (INIS)

Smith, D.B.; Miller, J.C.

1989-01-01

Mass-resolved multiphoton ionization (MPI) spectroscopy is an established technique for detecting and analyzing van der Waals molecules and larger clusters. MPI spectroscopy provides excellent detection sensitivity, moderately high resolution, and selectivity among cluster species. In addition to information provided by the analysis of photoions following MPI, photoelectron spectroscopy can reveal details regarding the structure of ionic states. Unfortunately, the technique is limited by its tendency to produce extensive fragmentation. Fragmentation is also a problem with other ionization techniques (e.g., electron impact ionization), but the intense laser beams required for MPI cause additional dissociation channels to become available. These channels include absorption of additional photons by parent ions (ion ladder mechanism), absorption of additional photons by fragment ions (ladder switching mechanism), and resonances with dissociative states in the neutral manifold. The existence of these dissociation channels can preclude the use of MPI spectroscopy in many situations. Recently, MPI studies of stable molecules using picosecond lasers (pulse length = 1 - 10 ps) have indicated that limitations due to fragmentation might be subdued. With picosecond lasers, dissociation mechanisms can be altered and in some cases fragmentation can be eliminated or reduced. Additional photon absorption competes effectively with dissociation channels when a very short laser pulse or, perhaps more importantly, a sufficiently high peak-power is used. In the case where ionic absorption and fragmentation occurs, it has been shown that picosecond MPI might favor the ion ladder mechanism rather than the ladder switching mechanism

Valence shell photoionization energies and cross-sections of NF sub 3 and PF sub 3

CERN Document Server

Jürgensen, A

2003-01-01

Relative outer valence shell ionization potentials and cross-sections were determined for the isostructural, Group 15, trifluorides NF sub 3 and PF sub 3 in the gas phase using synchrotron radiation. Excitation photon energies ranged from 70 to 160 eV. The experimental spectra were assigned and cross-sections analyzed with the aid of both MS-X alpha and ab initio calculations. Spectral differences in peak energies and relative intensities are related to structural and electronic differences between these two fluoride molecules. Valence shell ionization potentials were compared to calculated values obtained by several different methods. The partial photoionization cross-sections for each orbital were obtained as a function of excitation energy and compared to theoretical results obtained with the X alpha method.

Study of the three-step photoionization of uranium using a hollow cathode discharge tube

International Nuclear Information System (INIS)

Hu, Q.; Yin, L.; Zhang, Y.; Jin, C.; Cui, J.; Su, H.; Lin, F.

1986-01-01

The hollow cathode discharge (HCD) tube as a spectral light source has been developed. Because any element including refractory metals can be atomized by the cathode sputtering effect in HCD, a simple and reliable atomic vapor source produced by HCD has been widely used in laser spectroscopy. To the authors' knowledge, there is no previous work on the photoionization processes of metal atoms using an HCD tube. Here the authors report their study of the resonant three-step ionization of U in a homemade HCD tube

Photoionization Models of the H_2 Emission of the Narrow Line Region of AGNs

Science.gov (United States)

Aleman, I.; Gruenwald, R.

2011-05-01

The excitation mechanism of the narrow line region (NLR) of AGNs is still an open question. Excitation by UV radiation from O and B stars, x-rays from the central black hole, shock from supernovae or jets, or a combination of these mechanisms have been suggested. In the present work, we use photoionization models to study the excitation mechanisms of the H_2 infrared emission lines in the NLR. In the literature, analyzes of the H_2 emission have been done assuming that the molecules is present only in neutral regions (photodissociation regions, x-ray-dominated regions, or shocks; Veilleux et al. 1997, Krabbe et al. 2000, Rigopoulou et al. 2002, Rodriguez-Ardila et al. 2004, 2005, and Davies et al. 2005). However, they are not conclusive. In previous work (Aleman & Gruenwald 2004, 2011), we show that the H_2 emission from the ionized region of PNe can be significant for planetary nebulae (PNe) with hot central stars (T⋆ > 150000 K). Such stars produce copious amounts of high energy photons, which create an extended partially ionized region that favors the H_2 survival. The conditions in the NLR are similar to those in PNe with hot central stars, so we can expect that the H_2 emission might also be important. We obtain and analyze a grid of photoionization models for different NRL parameters. We study the resulting H_2 density and emission, as well as, the formation, destruction, excitation, and de-excitation mechanisms. The higher values observed for the H_2 1-0 S(1)/Brγ ratio cannot be reproduced by our models. The calculated ratios are between 10^-8 and 10^-1, while the observational ration can be as high as 10. The calculated ratio is strongly anti-correlated with the ionization parameter (U) and only models with U<10-3 result in ratios inside the observational range. We show that the NLR is an environment more hostile to the H_2 molecule than the ionized region of PNe. Another interesting result of our calculations is that the H_2 formation on grain surfaces

Demonstration of soft x-ray amplification by optical-field-induced ionization

International Nuclear Information System (INIS)

Midorikawa, Katsumi; Nagata, Yutaka; Kubodera, Shoichi; Obara, Minoru; Tashiro, Hideo; Toyoda, Koichi

1995-01-01

We have demonstrated the amplification of the 13.5-nm Lyman-α transition in hydrogen-like Li + ions, using a novel optical-field-induced ionization. A small-signal gain coefficient of 20 cm -1 was obtained. The use of preformed Li + plasma as an initial laser medium plays important roles for the production of suitable plasma conditions for an optical-field-induced ionization x-ray laser. (author)

Novel Application of Density Estimation Techniques in Muon Ionization Cooling Experiment

Energy Technology Data Exchange (ETDEWEB)

Mohayai, Tanaz Angelina [IIT, Chicago; Snopok, Pavel [IIT, Chicago; Neuffer, David [Fermilab; Rogers, Chris [Rutherford

2017-10-12

The international Muon Ionization Cooling Experiment (MICE) aims to demonstrate muon beam ionization cooling for the first time and constitutes a key part of the R&D towards a future neutrino factory or muon collider. Beam cooling reduces the size of the phase space volume occupied by the beam. Non-parametric density estimation techniques allow very precise calculation of the muon beam phase-space density and its increase as a result of cooling. These density estimation techniques are investigated in this paper and applied in order to estimate the reduction in muon beam size in MICE under various conditions.

Photoionization of atoms. Progress report, 1 April 1979-30 March 1980

International Nuclear Information System (INIS)

Samson, J.A.R.; Starace, A.F.

1979-12-01

A strong 304 A fluorescent signal from He + (n = 2) has been observed as a function of incident photon wavelength; strong autoionizing structure arising from 3n + states are seen in the spectrum. Measurements of the ratio of photoproduced Ne + ions to Ne 2+ ions indicate that further calibration of detector response is required. The dissociative photoionization of O 2 has been measured successfully as a necessary preliminary to measuring the photoionization cross section of atomic oxygen. The experimental apparatus has been built to measure the photoelectron angular distribution of atomic cesium. In order to measure rare gas photoionization cross sections to +-1% accuracy, a new gas tight window has been developed and second order lines in the laboratory light sources have been classified. A new random phase approximation (RPA) for the theoretical calculation of open- or closed-shell atom photoionization cross sections has been developed; the close-coupling approximation and the closed-shell atom RPA of Chang and Fano are limiting cases of a new set of coupled differential equations. The Rydberg energy spectrum and oscillator strengths of atomic hydrogen have been calculated for magnetic fields of order 10 5 Gauss using a basis of oblate spheroidal angle functions. Below N approx. = 12 an adiabatic approximation is excellent. Above n approx. = 12 non-adiabatic coupling terms rapidly become important, and the perturbed energy levels for n greater than or equal to 16 cross, indicating quasi-conserved dynamical symmetries. A previous calculation of the cesium 6s → epsilon p photoionization cross section has been extended to include interchannel coupling to the 5p → epsilon d photoionization channels; above the near threshold cross section minimum, the cross section is dominated by 5p → 5d resonance transitions

Electric field dependence of the total excimer luminescence of xenon excited below the atomic ionization limit

International Nuclear Information System (INIS)

Anon.

1987-01-01

In the spectral region of interest (i.e., 11.1 eV ≤ h nu ≤ 11.9 eV), the photoionization yield of electrons from excited-state dimers of xenon, increases monotonically to relatively high values (e.g., Y(11.7 eV) = 0.43 electrons/absorbed photon). It is also known however, that the luminescence intensity excited by photons in this region is quite high, even at low pressures. These two observations can be reconciled only by assuming that one of the processes leading to excimer luminescence involves dimer-ion + electron recombination. If this assumption is correct, application of an electric field, with concomitant collection of the free charges generated by the incident photons, should lead to a decrease in luminescence intensity; moreover, this decrease should follow the energy dependence of the photoionization yield function. The present report demonstrates experimentally that this is indeed the case. Such experiments combining luminescence and electric fields were made, until now, only by high-energy excitation. In this case the deconvolution of the various decay channels is hardly possible

Assessment of electron propagator methods for the simulation of vibrationally-resolved valence and core photoionization spectra

Science.gov (United States)

Baiardi, A.; Paoloni, L.; Barone, V.; Zakrzewski, V.G.; Ortiz, J.V.

2017-01-01

The analysis of photoelectron spectra is usually facilitated by quantum mechanical simulations. Due to the recent improvement of experimental techniques, the resolution of experimental spectra is rapidly increasing, and the inclusion of vibrational effects is usually mandatory to obtain a reliable reproduction of the spectra. With the aim of defining a robust computational protocol, a general time-independent formulation to compute different kinds of vibrationally-resolved electronic spectra has been generalized to support also photoelectron spectroscopy. The electronic structure data underlying the simulation are computed using different electron propagator approaches. In addition to the more standard approaches, a new and robust implementation of the second-order self-energy approximation of the electron propagator based on a transition operator reference (TOEP2) is presented. To validate our implementation, a series of molecules has been used as test cases. The result of the simulations shows that, for ultraviolet photoionization spectra, the more accurate non-diagonal approaches are needed to obtain a reliable reproduction of vertical ionization energies, but diagonal approaches are sufficient for energy gradients and pole strengths. For X-ray photoelectron spectroscopy, the TOEP2 approach, besides being more efficient, is also the most accurate in the reproduction of both vertical ionization energies and vibrationally-resolved bandshapes. PMID:28521087

The ionizing radiation of Seyfert 2 galactic nuclei

Science.gov (United States)

Ho, Luis C.; Shields, Joseph C.; Filippenko, Alexei V.

1993-01-01

We report the discovery of a nonrandom trend in the dispersion of emission-line intensity ratios for Seyfert 2 galaxies. The sense of this pattern suggests the influence of a single physical parameter, the hardness of the ionizing continuum, which controls the heating energy per ionizing photon. We compare the observed line ratios with new photoionization calculations and find that the observed distributions can be reproduced if the ionizing continuum is parametrized by a power law. Our results also suggest an inverse correlation between luminosity and continuum hardness for Seyfert 2 nuclei; if true, this trend extends a similar pattern known in quasars and Seyfert 1 galaxies to active galactic nuclei of lower luminosity. Samples of Seyfert 2 nuclei with improved selection uniformity are desirable for elaboration of these findings.

Determination of Optical-Field Ionization Dynamics in Plasmas through the Direct Measurement of the Optical Phase Change

International Nuclear Information System (INIS)

Taylor, A.J.; Omenetto, G.; Rodriguez, G.; Siders, C.W.; Siders, J.L.W.; Downer, C.

1999-01-01

This is the final report of a three-year Laboratory Directed Research and Development (LDRD) Project at Los Alamos National Laboratory (LANL). The detailed dynamics of an atom in a strong laser field is rich in both interesting physics and potential applications. The goal of this project was to develop a technique for characterizing high-field laser-plasma interactions with femtosecond resolution based on the direct measurement of the phase change of an optical pulse. The authors developed the technique of Multi-pulse Interferometric Frequency Resolved Optical Gating (MI-FROG), which recovers (to all orders) the phase difference between pumped and unpumped probe pulses, enabling the determination of sub-pulsewidth time-resolved phase and frequency shifts impressed by a pump pulse on a weak probe pulse. Using MI-FROG, the authors obtained the first quantitative measurements of high-field ionization rates in noble gases and diatomic molecules. They obtained agreement between the measured ionization rates an d those calculated for the noble gases and diatomic nitrogen and hydrogen using a one-dimensional fluid model and rates derived from tunneling theory. However, much higher rates are measured for diatomic oxygen than predicted by tunneling theory calculations

REVERBERATION AND PHOTOIONIZATION ESTIMATES OF THE BROAD-LINE REGION RADIUS IN LOW-z QUASARS

Energy Technology Data Exchange (ETDEWEB)

Negrete, C. Alenka [Instituto Nacional de Astrofisica, Optica y Electronica (Mexico); Dultzin, Deborah [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico (Mexico); Marziani, Paola [INAF, Astronomical Observatory of Padova, I-35122 Padova (Italy); Sulentic, Jack W., E-mail: cnegrete@inaoep.mx, E-mail: deborah@astro.unam.mx, E-mail: paola.marziani@oapd.inaf.it, E-mail: sulentic@iaa.es [Instituto de Astrofisica de Andalucia, E-18008 Granada (Spain)

2013-07-01

Black hole mass estimation in quasars, especially at high redshift, involves the use of single-epoch spectra with signal-to-noise ratio and resolution that permit accurate measurement of the width of a broad line assumed to be a reliable virial estimator. Coupled with an estimate of the radius of the broad-line region (BLR) this yields the black hole mass M{sub BH}. The radius of the BLR may be inferred from an extrapolation of the correlation between source luminosity and reverberation-derived r{sub BLR} measures (the so-called Kaspi relation involving about 60 low-z sources). We are exploring a different method for estimating r{sub BLR} directly from inferred physical conditions in the BLR of each source. We report here on a comparison of r{sub BLR} estimates that come from our method and from reverberation mapping. Our ''photoionization'' method employs diagnostic line intensity ratios in the rest-frame range 1400-2000 A (Al III {lambda}1860/Si III] {lambda}1892, C IV {lambda}1549/Al III {lambda}1860) that enable derivation of the product of density and ionization parameter with the BLR distance derived from the definition of the ionization parameter. We find good agreement between our estimates of the density, ionization parameter, and r{sub BLR} and those from reverberation mapping. We suggest empirical corrections to improve the agreement between individual photoionization-derived r{sub BLR} values and those obtained from reverberation mapping. The results in this paper can be exploited to estimate M{sub BH} for large samples of high-z quasars using an appropriate virial broadening estimator. We show that the width of the UV intermediate emission lines are consistent with the width of H{beta}, thereby providing a reliable virial broadening estimator that can be measured in large samples of high-z quasars.

SOLAR PHOTOIONIZATION RATES FOR INTERSTELLAR NEUTRALS IN THE INNER HELIOSPHERE: H, He, O, AND Ne

Energy Technology Data Exchange (ETDEWEB)

Bochsler, P.; Kucharek, H.; Möbius, E. [Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 (United States); Bzowski, Maciej; Sokół, Justyna M. [Space Research Center of the Polish Academy of Sciences, Ul. Bartycka 18A, 00-716 Warsaw (Poland); Didkovsky, Leonid; Wieman, Seth, E-mail: bochsler@space.unibe.ch [Space Sciences Center, University of Southern California, Los Angeles, CA 90089-1341 (United States)

2014-01-01

Extreme UV (EUV) spectra from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Solar EUV Experiment are used to infer photoionization rates in the inner heliosphere. Relating these rates to various proxies describing the solar EUV radiation, we construct a multi-linear model which allows us to extrapolate ionization rates back to periods when no routine measurements of the solar EUV spectral distribution have been available. Such information is important, e.g., for comparing conditions of the interstellar neutral particles in the inner heliosphere at the time of Ulysses/GAS observations with conditions during the more recent observations of the Interstellar Boundary Explorer. From a period of 11 yr when detailed spectra from both TIMED and three proxies—Solar and Heliospheric Observatory/CELIAS/SEM-rates, F10.7 radio flux, and Mg II core-to-wing indices—have been available, we conclude that the simple model is able to reproduce the photoionization rates with an uncertainty of typically 5%.

Multicomponent mixed dopant optimization for rapid screening of polycyclic aromatic hydrocarbons using ultra high performance liquid chromatography coupled to atmospheric pressure photoionization high-resolution mass spectrometry

KAUST Repository

Sioud, Salim

2012-05-04

RATIONALE To enhance the ionization efficiencies in atmospheric pressure photoionization mass spectrometry a dopant with favorable ionization energy such as chlorobenzene is typically used. These dopants are typically toxic and difficult to mix with water-soluble organic solvents. In order to achieve a more efficient and less toxic dopant, a multicomponent mixed dopant was explored. METHODS A multicomponent mixed dopant for non-targeted rapid screening of polycyclic aromatic hydrocarbons (PAHs) was developed and optimized using ultra high performance liquid chromatography (UPLC) coupled to atmospheric pressure photoionization high-resolution mass spectrometry. Various single and multicomponent mixed dopants consisting of ethanol, chlorobenzene, bromobenzene, anisole and toluene were evaluated. RESULTS Fourteen out of eighteen PAHs were successfully separated and detected at low pg/μL levels within 5 min with high mass accuracy ≤4 ppm. The optimal mixed multicomponent dopant consisted of ethanol/chlorobenzene/bromobenzene/anisole (98.975:0.1:0.9:0.025, v/v %) and it improved the limit of detection (LOD) by 2- to 10-fold for the tested PAHs compared to those obtained with pure chlorobenzene. CONCLUSIONS A novel multicomponent dopant that contains 99% ethanol and 1% mixture of chlorobenzene, bromobenzene and anisole was found to be an effective dopant mixture to ionize PAHs. The developed UPLC multicomponent dopant assisted atmospheric pressure photoionization high-resolution mass spectrometry offered a rapid non targeted screening method for detecting the PAHs at low pg/;μL levels within a 5 min run time with high mass accuracy a;circ4 ppm. Copyright © 2012 John Wiley & Sons, Ltd.

Photoionization in negative streamers : fast computations and two propagation modes

NARCIS (Netherlands)

Luque, A.; Ebert, U.M.; Montijn, C.; Hundsdorfer, W.

2007-01-01

Streamer discharges play a central role in electric breakdown of matter in pulsed electric fields, both in nature and in technology. Reliable and fast computations of the minimal model for negative streamers in simple gases such as nitrogen have recently been developed. However, photoionization was

The use of isoprene as a novel dopant in negative ion atmospheric pressure photoionization mass spectrometry coupled to high-performance liquid chromatography.

Science.gov (United States)

Dousty, Faezeh; O'Brien, Rob

2015-06-15

As in the case with positive ion atmospheric pressure photoionization (PI-APPI), the addition of dopants significantly improves the sensitivity of negative ion APPI (NI-APPI). However, the research on dopant-assisted-NI-APPI has been quite limited compared to the studies on dopant-assisted PI-APPI. This work presents the potential of isoprene as a novel dopant for NI-APPI. Thirteen compounds, possessing suitable gas-phase ion energetic properties in order to make stable negative ions, were selected. Dopants were continuously introduced into a tee junction prior to the ion source through a fused-silica capillary, while analytes were directly injected into the same tee. Then both were mixed with the continuous solvent from high-performance liquid chromatography (HPLC), nebulized, and entered the source. The nebulized stream was analyzed by APPI tandem quadrupole mass spectrometry in the negative ion mode. The results obtained using isoprene were compared with those obtained by using toluene as a dopant and dopant-free NI-APPI. Isoprene enhanced the ionization intensities of the studied compounds, which were found to be comparable and, in some cases, more effective than toluene. The mechanisms leading to the observed set of negative analyte ions were also discussed. Because in NI-APPI, thermal electrons, which are produced during the photoionization of a dopant, are considered the main reagent ions, both isoprene and toluene promoted the ionization of analytes through the same mechanisms, as expected. Isoprene was shown to perform well as a novel dopant for NI-APPI. Isoprene has a high photoabsorption cross section in the VUV region; therefore, its photoionization leads to a highly effective production of thermal electrons, which further promotes the ionization of analytes. In addition, isoprene is environmentally benign and less toxic compared to currently used dopants. Copyright © 2015 John Wiley & Sons, Ltd.