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Based on relativistic multichannel theory, this paper calculates the energy levels of autoionization Rydberg series 4s2nf(n = 4 − 23)Jπ = (7/2)° of scandium at different levels of approximation within the framework of multichannel quantum defect theory. The present results show that the dipole polarizations play an important role. Considering the dynamical dipole polarization effects, this paper finds that the difference between calculated and experimental quantum defects for the 4s2nf(n = 4 − 23)Jπ = (7/2)° series is generally about 0.01–0.03. Furthermore, the reason that 4s216f is obscured in experimental spectra is suggested to be the interaction with the neighbouring resonance state converged to 3d2(1G4)of Sc+.

A complete and accurate experimental test of theoretical spectroscopic data sets (state positions, lifetimes) available for the n = 3–5 terms of the 1s23lnl' Rydberg series of oxygen and neon ions is presented in a series of two papers. This result was achieved by fitting our high-resolution electron spectra with post-collisional lineshapes calculated with the help of these spectroscopic data. In this second paper we apply the fitting procedure described in the preceding companion paper (I) to the analysis of high-resolution electron spectra measured in O6+ (1s2) + He, H2 and Ne8+ (1s2) + He collisional systems at 10 qkeV collision energy (q is the ion charge). Singlet states alone are found to be excited in oxygen; they also explain most of the neon lines; in the latter case a possible contribution of triplet states is discussed. Many 1s23lnl' 1L transitions are identified for the first time. A quantitative comparison between measured and calculated positions clearly points to the best theoretical data currently available. Finally, a first identification of some 4l4l' 1L transitions observed in the neon spectrum is also proposed. From this huge spectroscopic work, we extract the first experimental partial branching ratios for autoionization into the 1s22l ionization continua for a large number of 1s23lnl' 1L states, which are compared with the total ones calculated by other authors; we deduce that populations of |ML | = 0 and 1 magnetic sublevels are nearly identical. The double-capture process is also briefly characterized by comparing relative populations of many n = 3–5 states; it is found that the same states are populated in O6+ + H2 and Ne8+ + He collisional systems with the same relative populations.

This paper presents the coronal ionization state distribution for argon. The calculations include ab initio rate coefficients for collisional excitation followed by autoionization (EA), and rates for direct ionization and dielectronic and radiative recombination. The EA rate coefficients have been fitted to analytical expressions, and the fitting coefficients are tabulated. The paper then presents the calculated radiative cooling coefficient for argon ions in a low-density plasma as a function of temperature. The channels for power loss from argon ions include collisional-radiative (CR) line emission, dielectronic and radiative recombination, and bremsstrahlung emission. The power emitted via CR line emission for each ion is tabulated on a grid of temperatures and densities. The total power loss coefficient is fitted to an analytical expression in powers of the temperature.

In a recent paper (Vrakking, M. J. J.; Lee, Y. T.; J. Chem. Phys. 1995, 102, 8833) we reported that autoionization rates of Xe Rydberg states converging on the P1/2 upper spin orbit state of Xe+ strongly depend on the presence of dc electric fields and surrounding ions. In the current paper, we present theoretical calculations that illustrate that the observed electric field dependence of the autoionization rates is influenced by the existence of short-range Rydberg electron-core interactions. In the presence of dc electric fields the autoionization rates decrease as a result of orbital angular momentum mixing. In the case of the ns′[1/2]1 series, mixing with the high-l manifold is mediated by short-range interactions with the rapidly autoionizing nd′[3/2]1 series. As a result, effective l-mixing takes place at substantially lower electric field strengths than would otherwise be the case. The experimental results of the dc electric field dependence of Xe pulsed field ionization (PFI) signals are compared with the theory, and predictions are made for sub-nanosecond timeresolved ionization experiments.

Positions, autoionization and radiative probabilities of Ne8+ (1s2 3l3l'), Ne8+ (1s2 3l4l') and some Ne8+ (1s2 4l4l') states have been calculated with the AUTOLSJ method and compared with other recent theoretical data. These results will be compared with the authors' experimental electron spectra in a companion paper. The theoretical basis of the electron spectra analysis discussed in the companion paper is also established. Various kinds of perturbations of the electron lineshapes and angular distributions (autoionization from a Stark state, post-collision effects and interferences) are presented in a unified fashion and discussed.

Autoionization resonance states are characterized by a complex potential energy surfaces, where the imaginary part is proportional to the decay rate. Sharp changes in the autoionization decay rates, with respect to the reaction coordinates, introduce reflections. That is, when the autoionization decay rate is very small outside the interaction region and large within it, the reactants will be reflected away from the interaction region. Consequently, the reaction is expected to be suppressed. However, no reflections was observed in the collision of H 2 with He in the 3P state [Nature Chemistry 7 (11) (2015) 921–926], for which the autoionization decay rate is very large in the interaction region and it is small elsewhere. In this paper, we theoretically investigate the reflection phenomenon within cold-chemistry collisions. Moreover, we present the conditions for which such reactions will not be suppressed due to reflections.

In this paper we present a protocol to evaluate partial and total Auger decay rates combining the restricted active space self-consistent field electronic structure method for the bound part of the spectrum and numerically obtained continuum orbitals in the single-channel scattering theory framework. Additionally, the two-step picture is employed to evaluate the partial rates. The performance of the method is exemplified for the prototypical Auger decay of the neon $1s{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}1}3p$ resonance. Different approximations to obtain the continuum orbitals, the partial rate matrix elements, and the electronic structure of the bound part are tested against theoretical and experimental reference data. It is demonstrated that the partial and total rates are most sensitive to the accuracy of the continuum orbitals. For instance, it is necessary to account for the direct Coulomb potential of the ion for the determination of the continuum wave functions. The Auger energies can be reproduced quite well already with a rather small active space. Finally, perspectives of the application of the proposed protocol to molecular systems are discussed.

Low-affinity materials (as MgO, CaO, LiF) are known to vary their Mie scattering profile with a changing charge. These materials are also predisposed to autoionize themselves. Although the oxides, opposite to lithium fluoride, are expected within the space environment, the presented investigations were carried out on LiF, since the aforementioned process shall be more pronounced. We are trapping a single grain in an electrodynamic quadrupole where the dust charge and its evolution can be estimated. By precise observations, we can register isolated hops of the grain charge which indicate the autoionization. A rate of this process varies with previous treatments of the object. While fresh grains exhibit one or a few hops within first 24 hours, the period between hops decreases to seconds, and the grain increases its charge by tens of elementary charges when the grains are treated by the electron beam with energy of 0.5–1 keV. On the other hand, ion treatment seems to stop the autoionization. The paper summarizes our observations and attempts to characterize the process itself.

We investigate whether the intrashell portion of the double-excitation spectrum of the helium atom may be interpreted in terms of collective rotational and bending vibrational motion, analogous to the ro-vibrational motion of molecules. Earlier work by us had identified a few levels in each atomic shell as having a rotorlike spectrum cutoff at higher energies, analogous to the cutoff rotorlike spectra of some nuclei. In this paper we use the I and d supermultiplets of the preceding paper of this journal, to interpret the entire intrashell manifold for each principal quantum number N, as resembling cutoff rotational and bending vibrational levels of a highly nonrigid linear symmetric XYX ''molecular'' structure. We obtain a good qualitative fit of each intrashell spectrum using leading-order ro-vibrational energy formulas from molecular spectroscopy including anharmonicity, centrifugal distortion, and rotation-vibration coupling. We interpret these effects for low-lying intrashell states of two-electron atoms, and find them to be consistent with an average equilibrium configuration theta/sub 12/=180/sup 0/ for the interelectronic angle. Analysis of the time scales of the proposed rotational, bending, and other degrees of freedom suggests approximate separability. We also identify parts of the spectrum analogous to molecular l doubling, and indicate a possible link betweenmore » the related Coriolis force and a recently proposed mechanism for decay by autoionization. Certain aspects of our collective interpretation of the atomic supermultiplets are discussed which have close parallels in nuclear physics, including the Elliott model and the SU(6) interacting boson model for nuclear collective motion.« less

In previous papers, U. Feldman, J. F. Seely, and A. K. Bhatia (J. Appl. Phys. 56, 2475 (1984)) and A. K. Bhatia, U. Feldman, and J. F. Seely (At. Data Nucl. Data Tables (in press)) have calculated atomic data and gain coefficients for ions of the Ne I isoelectronic sequence. Their calculations of electron impact excitation rates were carried out in the distorted wave approximation. They did not include the effect of resonance excitation, i.e., dielectronic capture by a Ne-like ion followed by autoionization leaving the Ne-like ion in an excited state. In this paper, we use the recent calculations of this process by B. W. Smith, J. C. Raymond, J. B. Mann, and R. D. Cowan (Astrophys. J. (in press)) to explore the effect of resonance excitation on gain coefficient calculations for the ion Fe XVII. We find substantial differences (factors of about 1.3--3) between gain coefficient calculations with and without the inclusion of resonances at low temperatures. However, these effects are not important at the temperatures considered by Feldman, Seely, and Bhatia for Fe XVII.

The paper gives an introduction into Interatomic and Intermolecular Coulombic Decay (ICD). ICD is an autoionization process, which contrary to Auger decay involves neighbouring sites of the initial vacancy as an integral part of the decay transition. As a result of ICD, slow electrons are produced which generally are known to be active in radiation damage. The author summarizes the properties of ICD and reviews a number of important experiments performed in recent years.Intermolecular Coulombic Decay can generally take place in weakly bonded aggregates in the presence of ionizing particles or ionizing radiation. Examples collected here mostly use soft X-rays produced by synchrotron radiation to ionize, and use rare-gas clusters, water clusters or solutes in a liquid jet to observe ICD after irradiation.Intermolecular Coulombic Decay is initiated by single ionization into an excited state. The subsequent relaxation proceeds via an ultra-fast energy transfer to a neighbouring site, where a second ionization occurs. Secondary electrons from ICD have clearly been identified in numerous systems. ICD can take place after primary ionization, as the second step of a decay cascade which also involves Auger decay, or after resonant excitation with an energy which exceeds the ionization potential of the system.ICD is expected to play a role whenever particles or radiation with photon energies above the ionization energies for inner valence electrons are present in weakly bonded matter, e.g., biological tissue. The process produces at the same time a slow electron and two charged atomic or molecular fragments, which will lead to structural changes around the ionized site.

Isolated-core-excitation (ICE) scheme and autoionization detection are employed to study the bound Rydberg states of europium atom. The high-lying states with odd parity have been measured using the autoionization detection method with three different excitation paths via 4f76s6p[8P5/2], 4f76s6p[8P7/2] and 4f76s6p[8P9/2] intermediate states, respectively. In this paper the spectra of bound Rydberg states of Eu atom are reported, which cover the energy regions from 36000 cm−1 to 38250 cm−1 and from 38900 cm−1 to 39500 cm−1. The study provides the information about level energy, the possible J values and relative line intensity as well as the effective principal quantum number n* for these states. This work not only confirms the previous results of many states, but also discovers 11 new Rydberg states of Eu atom.

The long-lived excited states of doubly charged rare gases can markedly affect their reactivity. In this paper we demonstrate the presence of strong state-specific effects in the charge exchange of Ar 2+ ( 3 P, 1 D and 1 S) with several neutral targets (He, Ne, Kr, Xe, D 2 , and CH 4 ). State sensitive measurements have been performed by producing the different Ar 2+ electronic states via tunable synchrotron radiation (Elettra-Trieste, Italy and SuperACO-Orsay, France). From the product ion yield data of charge transfer, state-selected total cross-sections have been deduced. Using the state-specific reactivity of Ar 2+ towards different neutral targets, it has been possible to extract the photon-energy-dependent production branching of the three doubly charged states and to investigate the autoionization dynamics of neutral or singly charged Ar in the vicinity of the double ionization threshold.

In this paper, we derive the double-resonance and single-resonance two photon absorption cross sections for zero electron kinetic energy (ZEKE) spectroscopy using the inverse Born–Oppenheimer approximation (IBOA) as a basis set. Quantum chemistry calculations can then be used to evaluate the ZEKE spectra. To show how to analyze the vibronic spectra of ZEKE spectroscopy, a couple of examples have been analyzed. Quantum chemistry calculations can be employed to obtain the potential surfaces of molecules and their ions, which can be used to calculate the Franck–Condon factors involved in the vibronic transitions. We also show that using the IBOA as a basis set, the autoionization of the ZEKE states can be calculated.

Resonant electronic spectroscopy consists in measuring a non-radiative decay process (Auger or autoionization process) excited with photon energies around an absorption edge. The resonant spectra carry information both on the nature of the electronic transitions near the absorption edge by scanning the very first empty orbitals above the Fermi level (through the absorption process), and, on the other hand, on the atomic electronic configuration through the lineshape of the observed decay process. In this paper, after a quick review of the pioneering works in this field, we show that resonant measurements and their theoretical modeling can be used to precisely interpret complex absorption spectra. Hence, Ce resonant 3d photoemission spectra allow, in the Ce-L3 edge, to attribute the two white lines to 4f1 and 4f0 final state electronic configurations and to evidence the presence of a hidden 4f2 structure in the rise of the absorption threshold. Quadrupolar transitions towards localized 3d orbitals are also detected and quantitatively characterized in the titanium K-edge prepeaks in TiO2, thanks to angular dependent resonant Ti-KLL Auger measurements.

Core hole spectroscopy has been shown to provide information on ultrafast charge transfer processes on a time scale of the core hole lifetime. In this paper we present high-resolution autoionization studies of SF6 and thiophene molecules adsorbed on a Ru(001) surface to further illustrate the potential of the so-called core hole clock method. Resonance states with very different core hole lifetimes can be excited with these sulfur-containing molecules. The selection of a specific resonant core hole excitation enables a variation of the time scale for probing electronic as well as nuclear dynamics.

In this paper, a theory of Coulomb explosion of molecules in intense laser fields based on the Auger effect will be presented. We first show how to calculate the rate of Auger process and then show that multiple ionization processes can be induced by the Auger effect alone or by the Auger effect followed by autoionization. For the case of molecules, multiple ionization is in general followed by dissociation.

In this paper, we report the photoabsorption and the constant ionic state spectroscopy of vinyl bromide (C 2H3Br). The photoabsorption spectrum was measured using synchrotron radiation and was investigated in detail between 5.0 and 12.0 eV photon energy revealing many previously unobserved structures. These features were analyzed in terms of valence to virtual valence transitions and Rydberg series. The examination of the three Rydberg series converging towards the first ionization threshold (2a" 1 ns, 2a" 1 np and 2a" 1 nd) leads to wave numbers of 335 ± 30, 690 ± 30 and 1305 ± 30 cm -1 . The vibrational wave numbers of the progressions belonging to Rydberg series converging towards the second ionization threshold are 485 ± 30 and 1145 ± 50 cm 1 . Ab initio calculations helped the assignment of the valence transitions and of the observed vibrational wave numbers in the Rydberg series. Constant ionic state spectra were recorded for vibronic states corresponding to the first and the second electronic states of the ion. Their fine structures are assigned to the autoionization of Rydberg states. The autoionization decay of these Rydberg states is analyzed qualitatively in terms of the vibrational nature of the final ionic state.

In this paper we present a theoretical study of the autoionization dynamics of high 2P1/2np′[3/2]1 Rydbergs (with the principal quantum numbers n=100–280) of Ar in weak homogeneous electric fields (F=0.01–1.0 V/cm), which were experimentally interrogated by time‐resolved zero‐electron kinetic energy (ZEKE) spectroscopy [M. Muhlpfordt and U. Even, J. Chem. Phys. 103, 4427 (1995)], and which exhibit a marked dilution (i.e., ∼2 orders of magnitude lengthening) of the lifetimes relative to those inferred on the basis of the n3 scaling law for the spectral linewidths of the np′ (n=12–24) Rydbergs. The multichannel effective Hamiltonian (Heff) with several doorway state(s) (for excitation and decay) and pure escape states (for decay) was advanced and utilized to treat the dynamics of the mixed Stark manifold of the ZEKE Rydbergs. Heff of dimension 2n−1 is then constructed for a n Rydberg manifold using independent experimental information on the (l dependent) quantum defects δ(l) and the (l, K, J dependent) dec...

In this paper we explore the level structure, the optical excitation modes and the dynamics of a mixed Stark manifold of very high Rydberg states (with principal quantum numbers n=80–250) of large molecules, e.g., 1,4 diaza bicyclo [2,2,2] octane (DABCO) and bis (benzene) chromium (BBC) [U. Even, R. D. Levine, and R. Bersohn, J. Phys. Chem. 98, 3472 (1994)] and of autoionizing Rydbergs of atoms [F. Merkt, J. Chem. Phys. 100, 2623 (1994)], interrogated by time‐resolved zero‐electron kinetic energy (ZEKE) spectroscopy. We pursue the formal analogy between the level structure, accessibility and decay of very high Rydbergs in an external weak (F≂0.1–1 V cm−1) electric field and intramolecular (interstate and intrastate) relaxation in a bound molecular level structure. The onset n=nM of the strong mixing (in an external field F and in the field exerted by static ions) of a doorway state, which is characterized by a low azimuthal quantum number l, a finite quantum defect δ, and a total nonradiative width Γs≂Γ0/...

Measurements are reported of Auger (autoionization) spectra of Ar and Kr produced by bombarding Al and Si substrates with Ar+ and Kr+ ions in the 110 eV-5 keV energy range. These are shown to be consistent with the simple Doppler model suggested, for Ne on Al and Si, in a previous paper. Once corrected using the model, the observed Auger energies are shown to correspond to theoretical predictions produced using Dirac-Fock calculations.

In this paper, we report the first rotationally resolved one- and two-color resonance enhanced multiphoton ionization photoelectron spectroscopy (REMPI-PES) study of the HCl molecule. The agreement between our experimental branching ratios and theoretical investigations is excellent. We also report the first zero kinetic energy pulsed field ionization (ZEKE-PFI) experiments carried out in a "magnetic bottle'' electron spectrometer. A direct comparison is made between ZEKE-PFI and REMPI-PES spectra for ionization via several rotational levels of the F 12(v'=0) and f 32(v'=0) Rydberg states of HCl. Large differences in both the spin-orbit and rotational branching ratios are found between the ZEKE-PFI and REMPI-PES spectra. These differences can be understood qualitatively on the basis of rotational and spin-orbit autoionization mechanisms. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.

In this paper we show how to employ the inverse Born-Oppenheimer approximation to establish a basis set to study zero kinetic energy (ZEKE) spectroscopy and the autoionization dynamics of the ZEKE Rydberg states. The calculations of vibrational and rotational autoionizations of a homonuclear diatomic molecule will be demonstrated as an example. The scaling laws for the autoionization rate constants are determined through nonlinear modeling of the calculated data.

Molecular frame photoemission is a very sensitive probe of the photoionization (PI) dynamics of molecules. The electron-ion vector correlation (VC) method takes advantage of dissociative photoionization (DPI) reactions of small molecules to measure such observables. It relies on the coincident detection of the photoelectron and the ion fragment emitted from the same DPI event and the determination of their velocity vectors. Most of the VC studies so far have been performed using synchrotron radiation (SR) light sources which benefit from a high repetition rate (1-10MHz) favorable for coincidence experiments. In this paper we discuss the extension of this method to the study of PI processes induced by ultra-short VUV light sources, which provide the capability for investigating processes characterized by femtosecond or subfemtosecond dynamics. We first illustrate the VC method by the report of recent results of a comparative study of resonant photoionization of the H2 and D2 molecules induced by VUV circularly polarized synchrotron radiation at SOLEIL in the region involving resonant excitation of Q1 and Q2 doubly excited state series. This problem is of particular interest since autoionization and dissociation of selected Q1 or Q2 states occur on a comparable time scale of few femtoseconds, which implies a coupling between the electronic and nuclear motion. The extension of the VC method using femtosecond laser sources is then demonstrated by results for multiphoton PI of the Xe atom induced by 70fs pulses centered at 400nm delivered by the SOFOCKLE and PLFA sources (SLIC, CEA-Saclay) after frequency doubling of a 1 kHz Ti:sapphire laser.

For pt.I see ibid., vol.24, no.7, p.1695-72 (1991). A thorough analysis of electron spectra measured at 80 keV in collisions between Ne8+ (1s2 ) ions and helium and molecular hydrogen targets is presented. The 1s2 3lnl' and 1s2 4lnl' lines are identified up to n=9. With helium, a fitting procedure for 1s2 3lnl' lines (all the lines for n=3, 4, and the first 3s5l ones), observed for the first time at different angles, make it possible to compare the authors' experimental results with two different theoretical data sets: their own theoretical values for positions, autoionization and radiative probabilities obtained by the AUTOLSJ method, which are given in a companion paper, and those recently published by Bachau et al. using a Feshbach method with a model potential. This allows the authors to test both theoretical positions and lifetimes of (3,n) states. The relative weight of the n=3, 4 and the first n=5 states is often angle dependent. The apparent, angle dependent, branching ratio for autoionization into the 2p and 2s continua of the (3,3) and the first (3,4) states is determined for several cases and discussed. Finally, differential and total cross sections are given and compared with other available experimental results.

Vibrational autoionization induced by the Renner-Teller interaction in linear polyatomic molecules is considered in the context of the three-state electrostatic model developed by Gauyacq and Jungen [Mol. Phys. 41, 383 (1980)]. For small interactions, simple formulas are derived for the quantum defect matrix elements and the autoionization rates in terms of the more common Renner-Teller parameters derived from spectroscopic analyses of low-lying Rydberg states. These formulas should provide guidance for empirical fitting of quantum defect parameters to spectra of high Rydberg states. Consideration of typical values of the Renner-Teller parameters also allows the estimation of vibrational autoionization rates induced by these interactions. These estimates support the validity of the Deltav=-1 propensity rule for vibrational autoionization. Constraints on the vibrational autoionization rates for the symmetric stretching vibration are also discussed. In the following paper, electron capture by polyatomic molecular ions into vibrationally autoionizing Rydberg states is considered from the same perspective, and a simple formula is derived to allow the estimation of the effect of this process on dissociative recombination cross sections.

The formalism developed in the preceding paper for vibrational autoionization via Renner-Teller active vibrations is adapted to treat dissociative recombination and applied to the reaction of HCO(+)+e(-). Existing spectroscopic data on the rovibrational structure of the HCO(+) (2)Sigma(+) ion and the HCO 3ppi (2)Pi Rydberg state are fitted by using the semirigid bender model to extract the parameters required to calculate the autoionization and electron capture widths. The results of this simple model are in good agreement with more detailed first principles calculations of the dissociative recombination cross section and confirm the earlier conclusion that coupling due to the Renner-Teller interaction is largely responsible for the observed dissociative recombination cross section at electron energies below approximately 0.1 eV.

Dielectronic data for state-specific F-like to Ne-like recombinations are obtained for elements between argon and krypton (and perhaps somewhat beyond). The data consist of energy levels, autoionization rates, radiative rates, and dielectronic-recombination branching ratios. Detailed calculations using a Hartree-Fock method that includes relativistic corrections, but no configuration interactions, were carried out for ${\mathrm{Ar}}^{9+}$, ${\mathrm{Ti}}^{13+}$, ${\mathrm{Fe}}^{17+}$, and Se $^{25+}$. Three- and four-parameter fits were then made to these data enabling one to calculate dielectronic rates for all elements in the fourth row of the periodic table. These scaling relations provide checks on the accuracy of the numerical methods used to obtain the Ar, Ti, Fe, and Se data. Further checks are provided by comparisons made to other published work. The dielectronic-recombination rates presented in this paper are very important in the calculation of population inversions and x-ray laser gain within neonlike ionization stages.

In this paper we discuss the single‐photon ionization dynamics of the d ^1Π_g Rydberg state of O_2. Comparison is made with vibrationally resolved measurements of photoelectron spectra which employ (2+1) resonance enhanced multiphoton ionization (REMPI) through the d ^1Π_g state. A σ_u shape resonance near the ionization threshold leads to non‐Franck–Condon vibrational branching ratios and a substantial dependence of photoelectron angular distributions on the vibrational state of the X ^2Π_g ion. Significant differences exist between our one‐electron predictions and experiment. These are mainly attributed to electronic autoionization of repulsive ^1∑^−_u , ^1∑^+_u , and ^1Δ_u states associated with the 1π^3_u 1π^3_g configuration. A proposed singlet "K" ^1Π_u Rydberg state converging to the A ^2Π_u ion probably also contributes to autoionization in the d ^1Π_g state spectrum. We also show that autoionizing H and J ^3Π_u Rydberg states of O_2 converging to the a ^4Π_u and A ^2Π_u ionic thresholds, respectively, may play a previously unsuspected role in the C ^3Π_g state one‐color REMPI spectra. We discuss multiplet‐specific (spin‐dependent) effects via comparison of these results with recent experimental and theoretical studies of O_2 C ^3Π_g photoionization.

The temperature and density dependence of the molecular and thermodynamic properties of water is investigated theoretically by means of the ab initio electronic structure theory combined with the reference interaction site model method, so-called RISM-SCF. We consider the autoionization process (H2O + H2O right harpoon over left harpoon H3O+ + OH-) by regarding H2O, H3O+, and OH- as "solute" molecules in an aqueous solution and evaluate molecular geometry, electronic structure, solvation structure, and the ionic product of water (pKw) of these species as functions of thermodynamic conditions. In our previous paper, we calculated these properties by using essentially the same method in a wide range of density values (0.6-1.4 g/cm3). However, the calculation was limited at rather higher density (>0.6 g/cm3) due to the difficulty of convergence, which is inherent to the hypernetted-chain (HNC) closure. The problem is overcome in this study by employing the Kovalenko-Hirata (KH) closure which hybridizes the HNC and the mean-spherical approximation (MSA). Here, we present the results for the thermodynamic range of densities from 0.025 to 1.0 g/cm3 and for temperatures from 300 to 800 K including the supercritical point.

Slow highly charged ions approaching surfaces at very close distances (∼nm) are known to capture many electrons in highly excited states forming hollow atoms(1)(2). These hollow atoms quickly decay to their ground states through a long cascade of autoionization processes( Auger transitions) which may be balanced , as these ions are still close to the surface, by a series of electron captures. This actual sequence of many events of capture and autoionization, alternate or not, is not experimentally known to date, and depends on the charge of the ions and of the capture processes which may be very different above metals and insulators. We review in this paper two new experiments on the kinematics of fully decelerated highly charged ions(Ar18+) above dielectric and metal surfaces, and on the behavior of ions of lower charge states (O7+ and Ne9+) above the same surfaces.

This paper investigates the possibility of suppressing the ionization rate in a magnetostatic trap of metastable neon atoms by spin-polarizing the atoms. Suppression of the ionization is critical for the possibility of reaching Bose-Einstein condensation with such atoms. We estimate the relevant long-range interactions for the system, consisting of electric quadrupole-quadrupole and dipole-induced dipole terms, and develop short-range potentials based on the Na_2 singlet and triplet potentials. The auto-ionization widths of the system are also calculated. With these ingredients we calculate the ionization rate for spin-polarized and for spin-isotropic samples, caused by anisotropy of the long-range interactions. We find that spin-polarization may allow for four orders of magnitude suppression of the ionization rate for Ne. The results depend sensitively on a precise knowledge of the interaction potentials, however, pointing out the need for experimental input. The same model gives a suppression ratio close to unity for metastable xenon in accordance with experimental results, due to a much increased anisotropy in this case., Comment: 15 pages including figures, LaTex/RevTex, uses epsfig.sty

In this paper we examine several processes‐primarily resonant processes‐occurring in electron‐ion collisions. Examples have been chosen which emphasize close ties of some of our own work with that of Chris Bottcher. We attempt to provide a perspective of the work ‘‘then’’ when the work was initially carried out and ‘‘now’’ after advances in the field. In particular, some examples are given in the areas of dissociative recombination, dielectronic recombination, excitation‐autoionization and resonant excitation multiple autoionization, and resonant excitation.

The method to calculate the rate coefficient of dielectronic recombination (DR) in dense plasma is discussed in this paper. The formula for calculating the DR rate coefficient as a function of electron density is derived under the effects of transition processes among doubly excited states, collisional ionization and autoionization corresponding to doubly excited states. And the calculation results for DR of Ne-like Ni based on the formula are given. The results show the trend of the change in DR rate coefficient as electron density increases. Additionally, the DR rate coefficients under the effects of different atomic processes are given and analyzed.

In this paper, two different detection methods, photoionization and autoionization, are combined to study the spectrum of highly excited states of Eu atom. On the one hand, the bound Eu spectrum with odd-parity in the region of 43927—45010 cm-1 has been measured. The spectral information, such as position and intensity, of 32 transitions can be deduced from the spectra with calibration and the error estimation. The information of excitation process and the selection rules enables us to determine their total angular momenta. Comparison with the related literature show that 12 of the states are newly discovered. On the other hand, we design an effective method to identify different types of highly excited states. The spectra of odd-parity states in the same region are measured by both photoionization and autoionization methods, from which we may separate the Rydberg states from the valence states. of the 32 transitions only 14 can be identified as Rydberg states, and the others are valence states. Furthermore, the effective quantum numbers of the Rydberg states are also discussed in detail with the quantum theory.

We present here in a format intermediate between a research‐revue paper and a student course some considerations about the calculation of the photoionization cross section for diatomic and small polyatomic molecular systems. Examples are taken from the work on diatomic molecules performed in Orsay, namely photoionization of CO, H2 and HI and the work on small polyatomic molecules, namely H2O and CH4, performed in the framework of a joint project between California Institute of Technology and several Universities in Brasil.

This paper describes electron emission following the autoionization of doubly excited states in Be-like ions. The Be-like Auger states are produced by two electron capture in slow C{sup 4+}, O{sup 6+} and Ne{sup 8+} ions. These measurements were performed by means of high resolution Auger electron spectroscopy on different target gases and at different projectile energies. Line assignments and relative cross sections are given for the investigated doubly excited states and the excitation mechanism is discussed. 15 refs., 16 figs., 4 tabs.

A recently developed time-of-flight photoelectron-photoelectron coincidence spectroscopy technique, which gives complete two-dimensional e(-)-e(-) spectra in single photon double ionization, is applied to molecular oxygen at photon energies below and above the adiabatic double ionization threshold of O(2). Analysis of the two-dimensional coincidence maps reveals specific indirect pathways for the double ionization process. Dissociative ionization paths with subsequent autoionization of atomic oxygen are found to be the dominant processes for all chosen photon energies. Spectra of the photoelectrons coincident with the autoionization electrons show that intermediate O(2)(+) states are involved which do not autoionize to molecular O(2)(2+). In particular, the ground state of O(2)(2+) is vibrationally resolved and shows a regular progression which can be well described by direct Franck-Condon transitions at an internuclear distance R(e)(X (1)Sigma(g)(+))=1.054 A. Quantum yields of double ionization for O(2), of a form discussed in this paper, are determined.

This reply offers further support for the assignments of the vibrational frequencies of C6 made in our original paper [C. C. Arnold, Y. Zhao, T. N. Kitsopoulos, and D. M. Neumark, J. Chem. Phys. 97, 6121 (1992)]. Two of our experimental frequencies are quite different from the corresponding ab initio values, and the resolution of this discrepancy clearly requires further theoretical work.

Electron Capture and transfer ionization by Ar(8–12)+ in collisions with argon atoms were studied by using the position sensitive and time-of-flight techniques. Some of the measured projectile charge changing cross sections (σq,q−k) and phenomenological cross sections (σrq,q−k) are reported in this paper. The measured cross sections are compared with the predictions of the molecular Coulombic overbarrier model by considering the autoionization decay and electron evaporation of multiply excited states in projectiles and recoil ions respectively.

In this paper, the effect of the spatial inhomogeneity of the laser field and the size of detector acceptance angle or aperture on strong-field autoionization photoelectron spectra is investigated. It is shown that the photoelectron spectra are drastically affected by the above factors , for small detector acceptance angle or aperture size, peak switching appears in the photoelectron spectra, but for large detector acceptance angle or aperture size, peak switching is destroyed completely.

In this paper, the two-photon autoionization involving second-order ionization processes is investigated. The photoelectron spectra are calculated, and the effects of second-order process on the photoelectron spectra and the relation of spectra's variation with intensity of light are emphatically analyzed.

A practical approach to calculating diagnostic parameters includes both scattering and statelike (autoionization) elements. The paper presents inelastic quasi-projection-operator calculations of autoionization states of the three-electron ions of oxygen and silicon for states below the n = 3 manifod of the respective two-electron parent (O VI and Si XII). Wave functions containing up to 40 configurations are calculated. The O VI calculated results agree with experimental results within the experimental error (about + or - 2 eV) while for the Si XII case, it was necessary to include relativistic effects. Where formulas are available (states for which p + q = 2), the Si XII results are also in good agreement with experimental results for 2Se, 2Po, and 2De states. Since the calculated results for some of the higher states did not agree with identifications proposed by Trabert et al. (1979), alternative identifications are suggested.

This paper describes a new technique for obtaining level positions, linewidths, autoionizing times, and oscillator strengths of core-excited levels and transitions. A tunable laser is used to deplete the population of a radiating core-excited level, as other levels within the core-excited manifold are accessed. A saturation technique which allows the measurement of autoionizing times whose linewidth lies well beneath the combined Doppler-hyperfine profile is developed and demonstrated.

This paper reports the status of current studies, primarily at ORNL, on low energy inelastic collisions of multicharged ions. A few specific measurements and theoretical predictions, which are discussed in other publications, are cited to illustrate present levels of understanding. Recent cross section measurements are presented for ionization of multiply charged ions by electron impact, and for electron capture by multiply charged ions from hydrogen atoms at low energies. For the alkali-like transition-series ions, Ti+3, Zr+3, and Hf+3, the excitation of an inner-shell electron, followed by autoionization (excitation-autoionization) dominates the total electron-impact ionization cross-section by more than an order of magnitude. For electron capture, the total cross-sections for C+q + H and O+q + H collisions (3 ≤ q ≤ 6) have been measured at energies ranging from 10-700 eV amu-1. For these few-electron systems at low energies, the capture cross-sections do not scale with ionic charge, or vary uniformly with velocity. Where detailed theory is available, agreement is generally satisfactory.

The fundamental aspects of excited dynamics in polyatomic molecules contains many effects, which while understood in the limit of a sparse density of states in a simple diatomic, have long eluded study. With a combination of lasers, supersonic beams to prepare ultra-cold molecules and novel types of spectroscopic approaches, one can begin to observe the dynamics and properties of superposition states which are the basis of phenomena ranging from autoionization, to predissociation, to quantum interference effects and intramolecular vibrational redistribution. This paper will review selected studies on large polyatomic molecules and their clusters.

This paper reports results of an experiment involving two‐laser resonance‐enhanced photoionization of benzene. The excitation sources were two frequency‐doubled dye lasers. The first laser pumped the molecule to a selected vibronic level of its first excited singlet state (1B2u), from where it was ionized by a time‐delayed pulse of the second laser. The ion yield depends on the intermediate vibronic state as well as on the wavelength of the ionizing laser. From the structures and intensities of the measured ion spectra we derived vibrational frequencies and molecular parameters of the ground electronic state of the ion to a remarkable accuracy. The contributions of autoionizing Rydberg levels to the ionization cross section can clearly be distinguished from direct ionization. Several resonance peaks were assigned to transitions to vibrational modes within these Rydberg states.

This paper presents for the first time an explicit calculation of the partial dielectronic-recombination-rate coefficients via the 3l3l' manifold for 17 neonlike ions ranging from argon to tungsten, using relativistic multiconfiguration wave functions to calculate both the Auger and radiative matrix elements. The effect of electron collisions on the dielectronic-recombination-rate coefficient is also examined at several densities of interest for modeling laboratory plasmas.

The important role of ionized atoms and molecules in many aspects of physical and chemical phenomena is being increasingly recognized. Typical research areas are astrophysics and interstellar molecular syntheses; plasma physics and fusion research; aeronomy and effects of ultraviolet irradiation on high atmosphere constituents; ion-molecule reactions; mass spectrometry; fundamental research on structural problems; behaviour of excited species; quantum theory of molecular structure and chemical kinetics. This paper emphasises the role of the autoionization process and discusses some of its characteristics, as well as the experimental methods used for its study.

In our laboratory we are studying Rydberg states of the Na2 molecule by optical-optical double resonance. We have already analysed the rotational interactions by means of the Multichannel Quantum Defect Theory (M.Q.D.T.)[1]. The aim of this paper is to summarize another part of our work concerning the dynamical effects and the autoionization process which governs our experimental method.