Showing papers on "Photoionization mode published in 2007"
TL;DR: In this article, the interplay of an intense laser field and the atomic/molecular potential during the electron motion after ionization was analyzed, and conditions to determine when the electron's oscillations in the strong laser field are approximately decoupled from its acceleration in the ionic potential, and when they are not.
Abstract: Using the example of laser-assisted photoionization, we analyse the interplay of an intense laser field and the atomic/molecular potential during the electron motion after ionization. We give conditions to determine when the electron's oscillations in the strong laser field are approximately decoupled from its acceleration in the ionic potential, and when they are not. Excellent agreement between analytical and numerical results allows us to assess the recipes for analysing interference structures in high harmonic generation in molecules.
60 citations
TL;DR: The photoionization and photoelectron spectroscopy of pure He droplets were investigated at photon energies between 24.6 eV and 28.0 eV, with results dominated by fast electrons produced via direct ionization, with a small contribution from very slow electrons with kinetic energies below 1 meV arising from an indirect mechanism.
Abstract: The photoionization and photoelectron spectroscopy of pure He droplets were investigated at photon energies between 24.6 eV (the ionization energy of He) and 28.0 eV. Time-of-flight mass spectra and photoelectron images were obtained at a series of molecular beam source temperatures and pressures to assess the effect of droplet size on the photoionization dynamics. At source temperatures below 16 K, where there is significant production of clusters with more than 10(4) atoms, the photoelectron images are dominated by fast electrons produced via direct ionization, with a small contribution from very slow electrons with kinetic energies below 1 meV arising from an indirect mechanism. The fast photoelectrons from the droplets have as much as 0.5 eV more kinetic energy than those from atomic He at the same photon energy. This result is interpreted and simulated within the context of a "dimer model", in which one assumes vertical ionization from two nearest-neighbor He atoms to the attractive region of the He2+ potential energy curve. Possible mechanisms for the slow electrons, which were also seen at energies below IE(He), are discussed, including vibrational autoionizaton of Rydberg states comprising an electron weakly bound to the surface of a large HeN+ core.
56 citations
TL;DR: In this article, the effect of electron correlation in the case of 4p photoionization of atomic cesium was studied and the multiconfiguration Dirack-Fock method was applied in the calculations.
41 citations
TL;DR: In this paper, the convergent close-coupling formalism was applied to describe direct double photoionization (DPI) of the valence $n{s}^{2}$ shell of alkaline-earth-metal atoms.
Abstract: We apply the convergent close-coupling formalism to describe direct double photoionization (DPI) of the valence $n{s}^{2}$ shell of alkaline-earth-metal atoms: beryllium $(n=2)$, magnesium $(n=3)$, and calcium $(n=4)$. We consider the range of photon energies below the onset of resonant and Auger ionization processes where the subvalent and core electrons can be treated as spectators. By comparing alkaline-earth-metal atoms with helium, we elucidate the role of the ground state and final ionized state correlations in DPI of various quasi-two-electron atoms.
33 citations
TL;DR: In this article, the photoionization cross section from the 3s3p 1P1 excited state has been measured in the energy region from the first ionization threshold up to 1.4 eV excess energy using a two-step photoionisation and saturated ionization technique in conjunction with an atomic beam source and a time-of-flight mass spectrometer.
Abstract: The photoionization cross section from the 3s3p 1P1 excited state has been measured in the energy region from the first ionization threshold up to 1.4 eV excess energy using a two-step photoionization and saturated ionization technique in conjunction with an atomic beam source and a time-of-flight mass spectrometer that enables the separation of the three stable isotopes of magnesium on the time axis. The absolute value of the photoionization cross sections from the 3s3p 1P1 excited state near the 3s ionization threshold has been measured as 90 ± 16 Mb (at 354.5 nm ionizing wavelength) for the dominating isotope (24Mg) whereas the value at the peak of the 3p2 1S0 auto-ionizing resonance has been determined as 785 ± 141 Mb. The present experimentally measured photoionization cross sections are compared with the existing experimental and theoretical work, showing excellent agreement.
22 citations
TL;DR: In this paper, the authors performed valence photoionization with high-brilliance vacuum ultraviolet radiation at the free-electron laser at Hamburg (FLASH) and showed that saturation occurs due to the depletion of the ground-state molecular target within each femtosecond radiation pulse.
Abstract: Valence photoionization of ${\mathrm{N}}_{2}$ has been performed with high-brilliance vacuum ultraviolet radiation at $h\ensuremath{
u}=38.5\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ from the free-electron laser at Hamburg (FLASH). As a function of fluence, saturation of photoionization occurs due to the depletion of the ground-state molecular target within each femtosecond radiation pulse. With increasing fluence, the vibrational envelope of the valence photoionization spectral distribution experiences radiation-field-induced changes.
19 citations
TL;DR: In this article, a theoretical description of attosecond photoionization in the presence of a strong laser field, based on the numerical solution of the Schrodinger equation, is extended to the case of p-shell ionization.
Abstract: A theoretical description of attosecond photoionization in the presence of a strong laser field, based on the numerical solution of the Schrodinger equation, is extended to the case of p-shell ionization. In particular, Ar(3p) photoionization is considered. The main difference between this case and the previously considered case of s-shell ionization stems from the interference of the two dipole allowed channels of p-shell photoionization, which determines the angular distribution of photoelectrons in the absence of the laser field. The latter additionally distorts the angular distributions. We also extend to the initial p-shell case the model based on the strong-field approximation (SFA), which has been suggested earlier. At high photoelectron energy and low laser intensity both calculations give similar results. However, at low electron energy the SFA is inadequate. The dependence of the angular distribution on the carrier-envelope phase and the effects of orbital polarization are considered.
19 citations
TL;DR: In this paper, photoionization cross section measurements from the 6s6p 1 P1 and 3 P1 excited states of barium at and above the first ionization threshold are presented.
Abstract: We present photoionization cross section measurements from the 6s6p 1 P1 and 3 P1 excited states of barium at and above the first ionization threshold. The experiments have been performed using a thermionic diode ion detector in a space charge limited mode in conjunction with a Nd:YAG laser system and the saturation technique to determine the photoionization cross sections. The absolute values of the photoionization cross section from the 6s6p 1 P1 and 3 P1 excited states at the first ionization threshold have been determined as 90 ± 14 Mb and 102 ± 15 Mb, respectively. The measured values of the photoionization cross section from the 6s6p 1 P1 excited state are compared with available experimental and theoretical work, while the absolute photoionization cross sections from the 6s6p 3 P1 excited state are reported for the first time. (Some figures in this article are in colour only in the electronic version)
18 citations
TL;DR: In this paper, the absolute values of the photoionization cross sections from the 5s5p 1P1 and 5s 5p 3P1 excited states of strontium at the first ionization threshold were measured using saturated absorption technique and a thermionic diode ion detector.
Abstract: We present experimentally measured absolute values of the photoionization
cross sections from the 5s5p 1P1 and 5s5p 3P1 excited
states of strontium at the first ionization threshold as 11.4±1.8 Mb
and 10.7±1.7 Mb respectively using saturated absorption technique
along with a thermionic diode ion detector in conjunction with a Nd:YAG
pumped dye laser system. These threshold photoionization cross sections
values have been utilized to determine the oscillator strengths of the
5s5p 1P1↦5snd 1D2 and 5s5p 3P1↦5snd 3D2 Rydberg transitions. The oscillator strength densities in the
continuum corresponding to the 5s5p 3P1 excited state have also
been determined by measuring the photoionization cross sections at five
ionizing wavelengths above the first ionization threshold. Smooth merging of
the discrete f-values into the oscillator strength densities has been
observed for the 5s5p 3P1↦5snd 3D2 series across the
ionization threshold.
18 citations
TL;DR: In this paper, it was shown that the reflection of photoelectrons produced by the photoionization of $3d$ Xe photoionizations affects greatly partial photoionisation cross sections of Xe with respect to the angular anisotropy parameters, both dipole and nondipole adding to all of them additional maximums and minimums.
Abstract: We demonstrate rather interesting manifestations of coexistence of resonance features in characteristics of the photoionization of $3d$ electrons in $\mathrm{Xe}@{\mathrm{C}}_{60}$. It is shown that the reflection of photoelectrons produced by the $3d$ Xe photoionization affects greatly partial photoionization cross sections of $3{d}_{5∕2}$ and $3{d}_{3∕2}$ levels and respective angular anisotropy parameters, both dipole and nondipole adding to all of them additional maximums and minimums. The calculations are performed treating the $3∕2$ and $5∕2$ electrons as electrons of different kinds with their spins ``up'' and ``down.'' The effect of ${\mathrm{C}}_{60}$ shell is accounted for in the frame of the ``orange'' skin potential model. It is essential that within the considered photon frequency region the presented resonance features are not affected by the ${\mathrm{C}}_{60}$ polarization.
17 citations
TL;DR: In this paper, the photoionization of Ne·CO complex in the energy region of 13.8-14.2 was investigated using a synchrotron radiation source in Hefei.
01 Mar 2007
TL;DR: In this paper, high-resolution photoionization experiments were carried out with beams of C III, N IV, and O V containing roughly equal amounts of ground-state and metastable ions.
Abstract: High-resolution photoionization experiments were carried out with beams of C III, N IV, and O V containing roughly equal amounts of ground-state and metastable ions. The energy scales of the experiments are calibrated with uncertainties of 1 to 10 meV depending on photon energy. These data favorably compare with state-of-the-art R-matrix calculations carried out on an energy grid with a spacing of 13.6 μeV.
TL;DR: The formation mechanism of multiply charged fullerene ions was discussed in terms of valence-electron excitation to antibonding unoccupied orbitals and/or spherical standing waves inside the cavity of a fullerenes.
Abstract: Partial cross sections for the photoion formation from C(60) and C(70) were determined from the yields of singly, doubly, and triply charged ions which were measured by mass spectrometry combined with tunable synchrotron radiation at hnu = 25-120 eV. The dependence of the detection efficiencies on the mass-to-charge ratio was evaluated by using the formula proposed by Twerenbold et al. Corrections of the detection efficiency were found to be critical for obtaining accurate partial cross sections for photoionization of fullerenes. Revisions were made of the partial cross-section curves for single and double photoionization of C(60) and C(70). The curve for triple photoionization of C(70) was newly proposed. The ratios between the cross sections for double and single photoionization increase with hnu and reach saturated values of 0.78 at 85 eV for C(60) and approximately 1.3 at 100 eV for C(70). In contrast, the ratios at 120 eV between the cross sections for triple and single photoionization of C(60) and C(70) amount to 0.14 and approximately 0.38, respectively. The formation mechanism of multiply charged fullerene ions was discussed in terms of valence-electron excitation to antibonding unoccupied orbitals and/or spherical standing waves inside the cavity of a fullerene. This excitation could be followed by Spectator Auger processes and transmission of the excess electronic energy among numerous vibrational degrees of freedom.
TL;DR: In this paper, the authors determined the dipole amplitudes and their relative phases that describe the C 1s photoionization dynamics in CS2 molecules with heavy atoms (sulfur) having 3p valence orbitals.
Abstract: With the full use of the experimental data obtained by multi-coincidence velocity-map imaging spectrometry, we have determined the dipole amplitudes and their relative phases that describe the C 1s photoionization dynamics in CS2. It has been found that the σ shape resonance at about 15 eV above the C 1s ionization threshold appears only in the dipole amplitude dfσ. We have also carried out time-dependent density functional theory calculations so as to better understand the photoemission dynamics and shape resonances in the C 1s photoionization of CS2 molecules with heavy atoms (sulfur) having 3p valence orbitals, which distinguish the present work from well-studied works such as on CO and CO2 molecules.
TL;DR: It is found that it will be advantageous to manifest the phase-dependent photoionization by choosing the target atoms with larger ionization potential, using laser with smaller carrier-frequency, and increasing the pulse intensity.
Abstract: In this paper, a scaling law of photoionization of atoms irradiated by intense, few-cycle laser pulses is established. The scaling law sets a relation to the phase-dependent ionization with the kinetic energy of photoelectrons, the duration and peak intensity of short pulses, and the ionization potential of the target atoms. We find that it will be advantageous to manifest the phase-dependent photoionization by choosing the target atoms with larger ionization potential, using laser with smaller carrier-frequency, and increasing the pulse intensity.
14 Mar 2007
TL;DR: In this article, the oscillator strength distribution in the discrete and continuous regions of the spectrum of helium from the 2s 1 S0 metastable state has been determined using a Nd: yttrium aluminum garnet YAG pumped dye laser system in conjunction with a low pressure rf glow discharge.
Abstract: The oscillator strength distribution in the discrete and continuous regions of the spectrum of helium from the 2s 1 S0 metastable state has been determined using a Nd: yttrium aluminum garnet YAG pumped dye laser system in conjunction with a low pressure rf glow discharge. The saturation technique has been employed to determine the photoionization cross section from the 2s 1 S0 excited state at and above the first ionization threshold. The measured value of the photoionization cross section at the ionization threshold has been used to extract the f values for the 2s 1 S →np 1 P Rydberg series from n=10 ton=52. The f values of the observed Rydberg series decrease smoothly with an increase of the principal quantum number. In the continuum region the oscillator strength densities have been estimated by measuring the photoionization cross sections from the 2s 1 S0 excited state at five ionizing laser wavelengths above the first ionization threshold. The discrete f values smoothly merge into the continuous oscillator strength densities across the ionization threshold.
TL;DR: In this paper, the electron transfer from the neutral excited state to water was investigated, and electron transfer was shown to be efficient in the wavelength range of 220-290nm. But electron transfer process was not discussed.
Abstract: Excitation wavelength dependence ( λ ex = 220–290 nm) of photoionization quantum yields ( Φ ion ) of indole and tryptophan in water were directly obtained through nanosecond time-resolved transient absorption measurements. Monophotonic photoionization occurred efficiently in this wavelength range. We conclude that photoionization proceeds through electron transfer from the neutral excited state to water by comparing the Φ ion versus λ ex dependences with the ground-state spectra. Mechanism of the electron transfer process is discussed.
TL;DR: Two methods based on vacuum ultraviolet (vuv) photoionization are presented for the determination of the spin-orbit branching fractions of the halogen atom produced in the photodissociation of halogenated hydrocarbons.
Abstract: Two methods based on vacuum ultraviolet (vuv) photoionization are presented for the determination of the spin−orbit branching fractions of the halogen atom produced in the photodissociation of halogenated hydrocarbons. Both methods make use of differences in the photoionization cross sections of the 2P3/2 ground state and the 2P1/2 excited-state of the neutral halogen atom. In the first approach, measurements of the total photoionization signal of the halogen atom are made at several vuv wavelengths, and the difference in the wavelength dependences for the 2P3/2 and 2P1/2 atoms allows the extraction of the branching fractions. In the second approach, the vuv wavelength is set close to the ionization threshold of the 2P3/2 atom (well above that of the 2P1/2 atom), and measurements are made at several electric field strengths, which shift the ionization threshold and thus vary the photoionization cross sections. In both methods, the relative cross sections of the ground- and excited-state atoms are determin...
TL;DR: In this article, a variational R-matrix method was used to calculate state close-coupling approximations in the photon wavelength range 15-35 nm. And the detailed photoionization processes of included multichannels are displayed in the partial photoionisation cross sections, which contain a number of autoionizing Rydberg series of resonances converging to the C3+ 2p, 3s, 3p and 3d thresholds.
Abstract: Resonance structures and their characteristics in the photoionization of the first excited p-states of Be-like C2+ ion which interact with the even-parity continua have been studied up to the C3+ 3d threshold limit. Using the variational R-matrix method, calculations have been performed in the initial 20 and final 22 state close-coupling approximations in the photon wavelength range 15–35 nm. The detailed photoionization processes of included multichannels are displayed in the partial photoionization cross sections, which contain a number of autoionizing Rydberg series of resonances converging to the C3+ 2p, 3s, 3p and 3d thresholds. In particular, the lower members of the Rydberg series showing irregular patterns of resonances, which lie above the C3+ 2p threshold, are identified and resonance positions Er, effective quantum numbers n*, and widths Γ are presented. Excellent agreement between length and velocity gauge results is found, along with overall good agreement with previous work, except for the discrepancies with the threshold behaviour of the OP (opacity project) result.
TL;DR: In this paper, the vibrational branching ratio for the totally symmetric mode ν 1+ is found to be strongly affected by resonant excitation in the SiF4+ (DA12) photoionization channel.
Abstract: The authors report a fully vibrationally resolved photoelectron spectroscopy investigation of a nonplanar molecule studied over a range of excitation energies. Experimental results for all four fundamental vibrational modes are presented. In each case significant non-Franck-Condon effects are seen. The vibrational branching ratio for the totally symmetric mode ν1+ is found to be strongly affected by resonant excitation in the SiF4+ (DA12) photoionization channel. This is shown to be the result of two distinct shape resonances, which for the first time have been both confirmed by theoretical calculations. Vibrationally resolved Schwinger photoionization calculations are used to understand the vibronic coupling for the photoelectrons, both using ab initio and harmonic vibrational wave functions.
TL;DR: Sanchez and Martin this paper investigated photoionization of HeH+ in the 40-80 eV photon energy range using the theoretical method of Sanchez and Martin (1997 Phys. Lett. 79 1654; 1998 Phys. A 57 1006), which includes all electronic and vibrational degrees of freedom as well as the interferences between all possible ionization and dissociation channels.
Abstract: Photoionization of HeH+ in the 40–80 eV photon energy range is investigated using the theoretical method of Sanchez and Martin (1997 Phys. Rev. Lett. 79 1654; 1998 Phys. Rev. A 57 1006), which includes all electronic and vibrational degrees of freedom as well as the interferences between all possible ionization and dissociation channels. Integral and differential cross sections in the energy of the remaining ions as well as energy positions and autoionization widths of the HeH+ doubly excited states of 1Σ+ and 1Π symmetries have been evaluated. The results show that dissociative ionization leading to He+(1s) + H+ + e− entirely dominates the photoionization spectrum and that resonant effects due to autoionization are barely visible either in the integral or the differential cross sections. This is at variance with photoionization of the isoelectronic H2 molecule.
TL;DR: In this paper, a new theoretical model of the atomic oxygen photoionization cross section combined with a new solar minimum spectral irradiance model enables calculations at very high spectral resolution (0.001 nm).
Abstract: [1] Accurate knowledge of photoionization rates is fundamental for the study and understanding of gases in the solar system. Past calculations of the photoionization rates of atmospheric gases lack the spectral resolution to accommodate highly structured autoionization features in the photoionization cross section. A new theoretical model of the atomic oxygen photoionization cross section combined with a new solar minimum spectral irradiance model enables calculations at very high spectral resolution (0.001 nm). Our analysis of unattenuated photoionization rates reveals no strong coincidences among myriad bright solar emission lines and autoionization lines in the cross section. However, deeper in the terrestrial atmosphere, opacity effects are significant and the need for high spectral accuracy becomes increasingly important. In our solar minimum example, factor of 3 errors occur when the lower thermospheric photoionization rate of atomic oxygen is computed at 1 nm spectral resolution for both the cross section and solar flux.
TL;DR: In this paper, a model of a hollow atom as a hydrogen-like multicharged ion located at the center of a spherical shell formed by highly excited electrons was proposed and the photoionization cross sections of the inner 1s level of the ion were calculated.
Abstract: Within the framework of a model of a hollow atom as a hydrogenlike multicharged ion located at the center of a spherical shell formed by highly excited electrons, the photoionization cross sections of the inner 1s level of the ion have been calculated. The results show that the existence of the outer electronic shell of the hollow atom results in oscillations in the energy dependence of the photoionization cross section. It has been demonstrated also that the photoionization cross section as a function of photon energy is extremely sensitive to the magnitude of the discontinuity of the electric field at the surface of the outer electronic shell.
TL;DR: In this paper, close coupling calculations based on an R-matrix formalism are performed for the 1s?2p resonance photoionizations from the low-lying states of boron-like carbon ions.
Abstract: Close-coupling calculations based on an R-matrix formalism are performed for the 1s?2p resonance photoionizations from the low-lying states of boron-like carbon ions. The resonance energies, widths and oscillator strengths of 1s?2p core excitations are determined by analysing the calculated photoionization cross sections. Our calculations are in reasonable agreement with the experimental and theoretical results presented by other authors. The present numerical values may help to analyse the astrophysical and laboratory plasmas.
TL;DR: A brief review on photoionization and subsequent Auger decay in atoms, small molecules and clusters is given in this article, where illustrative examples are presented in order to show the progress in the field, emphasized by the recent high resolution measurements of Oulu electron spectroscopy group at the MAX synchrotron radiation facility.
TL;DR: In this article, the double-electron ejection process after photon absorption by an atom near the inner-atomic shell threshold is considered and a quantum-mechanical approach has been developed to take into account the contribution to the cross section of amplitudes of all three processes.
Abstract: The double-electron ejection process after photon absorption by an atom is considered near the inner-atomic shell threshold. The aim of our work is to clarify the dynamics of double-electron emission. For this purpose, it is of primary importance to investigate processes with well-defined final ionic states. The focus of our study in this case is resonant reactions with a low energy for one electron, whereas the energy of the other one is close to the energy of the Auger electron. In this case, important contributions to the cross section of three different processes have to be considered: (1) photoionization of the inner shell followed by Auger decay of the inner vacancy influenced by post-collision interaction (PCI); (2) the PCI capture of the slow photoelectron into a discrete state followed by valence multiplet decay, and (3) the double photoionization of the outer shell. A quantum-mechanical approach has been developed to take into account the contribution to the cross section of amplitudes of all three processes. This model is applied to the case of double photoionization of the Kr atom near the 3d-shell threshold. Our calculation predicts an interference effect in the channel of the 1D final state, whereas in the 3P final state channel the role of interference is negligible.
25 Jun 2007
TL;DR: In this paper, a simple blackbody surface emitter model was used to investigate the thermochemical nonequilibrium behind a strong argon shock wave with precursor photoionization, and it was shown that the photoexcited state of argon can accelerate electron-impact ionization behind the shock wave.
Abstract: Thermochemical nonequilibrium behind a strong argon shock wave with precursor photoionization was numerically investigated using a simple blackbody surface emitter model. The propagation Mach number of the shock wave is 41. Results showed that precursor photoionization drastically reduces the nonequilibrium region because electrons produced in the precursor region accelerates electron-impact ionization behind the shock wave. In addition, the computation reproduced the distribution of the measured electron number density behind the shock wave, although it overestimated the electron number density in the precursor region due to ignoring indirect photoionization from the photoexcited state of argon in the computation.
TL;DR: In this article, the effect of the internal energy of the radicals on the fragmentation dynamics of the parent photoion is discussed for the general case, and then for specific C3H5 radicals.
Abstract: The combination of ultraviolet (uv) photodissociation, vacuum-ultraviolet (vuv) photoionization, and velocity-map ion imaging is used to explore the dissociative ionization of allyl and 2-propenyl C3H5 radicals that have significant amounts of internal energy. The effect of the internal energy of the radicals on the fragmentation dynamics of the parent photoion is first discussed for the general case, and then for the specific C3H5 radicals. The results are relevant to an increasing number of studies in which single-photon vuv photoionization is used as a ‘soft’ ionization method for radicals produced in photodissociation and reactive scattering experiments, as well as in reactive environments such as flames and plasmas. †The submitted manuscript has been created by UChicago Argonne LLC, Operator of Argonne National Laboratory, (‘Argonne’). Argonne a US Department of Energy Office of Science Laboratory, is operated, under Contract No. DE-AC02-06CH11357 with the U.S. Department of Energy. The U.S. Governme...
15 Sep 2007
TL;DR: In this paper, an idea of the principles of various laser isotope separation methods, the current status of studies in this field, and industrial applications of laser IS separation techniques are given in a concise form.
Abstract: This paper gives in a concise form, an idea of the principles of various laser isotope separation methods, the current status of studies in this field, and industrial applications of laser isotope separation techniques.
Keywords:
separation;
isotope;
photoionization;
photodissociation;
laser;
multiphoton