Valence-shell photoionization of the Cℓ-like ion Ar + : Experiment and theory (original) (raw)
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L-shell photoionization of Ar^{+} to Ar^{3+} ions
Physical Review A, 2012
Absolute photoionization cross sections of Ar + , Ar 2+ , and Ar 3+ ions have been measured in the 250-280 eV photon energy range. These results are compared to theoretical cross sections extracted from two new calculations we performed. They reproduce well the general behavior of the experimental spectra and the magnitude of the direct photoionization cross sections. However, the oscillator strength of the resonant structure in the spectra, dominated by 2p → 3d transitions, is overestimated up to 80% by our calculations.
Valence-shell photoionization of chlorinelike Ar^{+} ions
2011
Photoionization (PI) of ions is a fundamental process of importance in many high-temperature plasma environments, such as those occurring in stars and nebulae [1] and in inertial-confinement fusion experiments [2]. Quantitative measurements of photoionization cross sections for ions provide precision data on ionic structure and guidance to the development of theoretical models of multielectron interactions.
The Absolute Cross Section forL‐Shell Photoionization of C+Ions from Threshold to 105 eV
The Astrophysical Journal Supplement Series, 2001
The absolute cross section for photoionization of C`ions has been measured from the ionization threshold at 24 eV to 105 eV by overlapping an ion beam with a monochromatized synchrotronradiation beam from the ASTRID undulator. The measurements, which are important for astrophysical modeling of, for example, stellar atmospheres, have been compared with R-matrix calculations from the Opacity Project and the Iron Project. The general agreement between theory and experiment is good, yet di †erences in the magnitude of the cross section of up to 50% are observed as well as some deviations concerning the resonance structure. Subject headings : atomic data È atomic processes
Multielectron photoionization to the3p44pconfiguration ofAr+: Experiment and theory
Physical Review A, 1986
Short-pulse (100-psec) soft-x-ray excitation from a laser-produced plasma and fast optical detection have been used to study multielectron photoionization from the 3p neutral ground state to the ten terms of the 3p 4p configuration of Ar+. Good agreement between measured populations and those obtained from an excitation model based on energy-dependent cross sections calculated with a relativistic Hartree-Fock atomic physics code using configuration interaction techniques was obtained. A 100-psec duration soft-x-ray pulse from a laserproduced plasma combined with a subnanosecond optical detection system has been used to study electron correlations in Ar by observing multielectron photoiomzation from the 3ps ground state of neutral Ar to the 3p 4p configuration of Ar+. Measured population densities of the ten LS terms of this configuration produced by direct two-electron photoionization are in reasonably good agreement with those predicted by an excitation model based upon calculated photoionization cross sections to these ten terms and a measured soft-x-ray flux equivalent to an approximately 23-eV blackbody. The energy-dependent cross sections were computed with an atomic physics code using configuration interaction (CI) techniques. The sum of two of the calculated partial cross sections, with a peak value of 0.06 Mb at 40 eV (310 A), agrees within 30% over a wide range of energies with a cross section for those terms deduced from satellite intensities measured with photoelectron spectroscopy.
Valence-shell photoionization of the chlorinelike Ca3+ ion
Absolute photoionization measurements were performed for a mixture of 2Po 3/2 ground-state and 2Po 1/2 metastable-state Ca3+ ions over the photon energy range 65.7–104.6 eV by merging an ion beam with a beam of monochromatized synchrotron radiation. The ionization threshold energy of the 2Po 3/2 ground state was measured to be 67.063 ± 0.015 eV, which is 0.207 eV lower than the value tabulated in the NIST database. Most of the observed resonances associated with multiple Rydberg series of autoionizing states have been assigned spectroscopically using the quantum defect form of the Rydberg formula, guided by relativistic Hartree-Fock calculations of resonance energies and oscillator strengths. Intermediate coupling R-matrix calculations performed using the semi-relativistic Breit-Pauli approximation are in suitable agreement with measured absolute photoionization cross section in the energy range studied for this complex Cl-like ion species.
Photoionisation of Ca + ions in the valence- energy region 20–56eV: experiment and theory
Relative cross sections for the valence shell photoionisation (PI) of S 2 ground level and D 2 metastable Ca + ions were measured with high energy resolution by using the ion–photon merged-beams technique at the Advanced Light Source. Overview measurements were performed with a full width at half maximum bandpass of E 17 D = meV, covering the energy range 20–56eV. Details of the PI spectrum were investigated at energy resolutions reaching the level of E 3.3 D = meV. The photon energy scale was calibrated with an uncertainty of ±5meV. By comparison with previous absolute measurements the present experimental high-resolution data were normalized to an absolute cross-section scale and the fraction of metastable Ca + ions that were present in the parent ion beam was determined to be 18% ±4%. Large-scale R-matrix calculations using the Dirac Coulomb approximation and employing 594 levels in the close-coupling expansion were performed for the s p s Ca 3 3 4 S 2 6 2 1 2 + ()and s p d Ca 3 3 3 D 2 6 2 3 2,5 2 + () levels. The experimental data are compared with the results of these calculations and previous theoretical and experimental studies.
2003
Аннотация We have investigated valence-shell photoionization (PI) of 1 S ground state and 3 P o metastable states of C 2+ ions. Absolute PI cross-sections were measured in the range 40.7-56.4 eV with an energy spread of 30 meV using a photon-ion merged beams arrangement at the Advanced Light Source (ALS). Detailed calculations based on the semi-relativistic Breit-Pauli R-matrix approach suggest a fraction of 40% of metastable ions in the primary beam of the experiment.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2011
Three-photon double ionization of an Ar atom has been investigated by photoelectron spectroscopy using an extreme ultraviolet free-electron laser. When the photon energy of the laser has been tuned to the resonances of the intermediate Ar + ion, photoelectron peaks due to the resonant two-photon single ionization of the Ar + ion have been observed. And it has been revealed that the appearance of the peaks is controlled by the mixing ratios of 3p 4 core-configurations of the multi-configuration states. Furthermore, it has been shown that the laser intensity dependence of the Ar 2+ ion production rate due to the resonant two-photon single ionization strongly deviates from that expected by perturbation theory.
First Observation of Photoelectron Spectra Emitted in the Photoionization of a
The first measurement of photoelectron spectra emitted in the photoionization of a singly charged-ion beam by synchrotron radiation is reported. A Ca -ion beam is resonantly photoionized by the monochromatized photon beam of the SU6 undulator of the SuperACO Storage Ring at 33.20 eV photon energy. The values observed for the kinetic energy and for the intensity of the photoelectron line are in good agreement with the predicted values. The success of this feasibility experiment opens up wide opportunities for similar photoionization and Auger studies on multiply charged ions.
Photodissociation of Ar+3 cluster ion
Chemical Physics Letters, 1990
The time-of-flight spectra of Ar+ produced in the photodissociation of Ar: were observed in the wavelength range of 460-590 nm. Analysis revealed that (I) the kinetic energy distribution of Ar* fragments is bimodal: the components having a released kinetic energy of x0.5-1.0 eV (fast component) and almost zero kinetic energy (slow component), (2) the fragment angular distribution displays an anisotropy characteristic of direct dissociation involving a parallel-type transition, and (3) the formation of the fast component is the dominant channel with a branching fraction more than 80%. A dissociation mechanism involving a linear symmetric precursor is proposed on the basis of ab initio calculations for the potential energy surfaces of Ar:.