K-shell photoionization of O+ and O2+ ions: Experiment and theory (original) (raw)
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K-shell photoionization of O 4 + and O 5 + ions: experiment and theory
Absolute cross-sections for the K-shell photoionization of Be-like (O 4 +) and Li-like (O 5 +) atomic oxygen ions were measured for the first time (in their respective K-shell regions) by employing the ion–photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/E ≈ 3200 (≈170 meV, full width at half-maximum) was achieved with photon energy from 550 to 670 eV. Rich resonance structure observed in the experimental spectra is analysed using the R-matrix with pseudo-states (RMPS) method. Results are also compared with the screening constant by unit nuclear charge (SCUNC) calculations. We characterize and identify the strong 1s → 2p resonances for both ions and the weaker 1s → np resonances (n ≥ 3) observed in the K-shell spectra of O 4 + .
K-shell photoionization of B-like oxygen (O3+) ions: experiment and theory
Absolute cross sections for the K-shell photoionization of boron-like (B-like) O3+ ions were measured by employing the ion–photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/ Delta E=5000 (110 meV), full width half maximum) was achieved with(photon energy from 540 up to 600 eV. Several theoretical approaches, including R-matrix, multi-configuration Dirac–Fock and screening constant by unit nuclear charge were used to identify and characterize the strong 1s -> 2p and the weaker 1s -> 3p resonances observed in the K-shell spectra of this ion. The trend of the integrated oscillator strength and autoionization width (natural line width) of the strong 1s -> 2p resonances along the first few ions of the B-like sequence is discussed.
arXiv: Atomic Physics, 2016
Absolute cross sections for the {\it K}-shell photoionisation of Be-like (O$^{4+}$) and Li-like (O$^{5+}$) atomic oxygen ions were measured for the first time (in their respective {\it K}-shell regions) by employing the ion-photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/$\Delta$E approx\approxapprox 3200 ($\approx$ 170 meV, FWHM)was achieved with photon energy from 550 eV up to 670 eV. Rich resonance structure observed in the experimental spectra is analysed using the R-matrix with pseudo-states (RMPS) method. Results are also compared with the screening constant by unit nuclear charge (SCUNC) calculations. We characterise and identify the strong rm1srightarrow2p\rm 1s \rightarrow 2prm1srightarrow2p resonances for both ions and the weaker rm1srightarrownp\rm 1s \rightarrow nprm1srightarrownp resonances ($ n \ge 3$) observed in the {\it K}-shell spectra of O$^{4+}$.
Low-energy fine-structure resonances in photoionization of O ii
Physical Review A, 2010
Resonant features in low-energy photoionization cross sections are reported in coupled-channel calculations for O II including relativistic fine structure. The calculations reveal extensive near-threshold resonant structures in the small energy region between the fine structure levels of the ground state 2p 2 ( 3 P 0,1,2 ) of the residual ion O III. Although the resonances have not yet been observed, they are similar to other experimentally observed features. They are expected to significantly enhance the very-low-temperature dielectronic recombination rates, potentially leading to the resolution of an outstanding nebular abundances anomaly. Higher energy partial and total photoionization cross sections of the ground configuration levels 2p 3 ( 4 S o 3/2 , 2 D o 3/2,5/2 , 2 P o 1/2,3/2 ) are found to be in agreement with experimental measurements on synchrotron-based photon sources [1-3], thereby identifying the excited O III levels present in the ion beams. These are also the first results from a recently developed version of Breit-Pauli R-matrix (BPRM) codes, with inclusion of two-body magnetic interaction terms. The improved relativistic treatment could be important for other astrophysical applications and for more precise benchmarking of experimental measurements.
Absolute photoionization cross section measurements of O II ions from 29.7 to 46.2 eV
2008
ABSTRACT Absolute photoionization cross sections have been measured for a mixture of ground-state and metastable O II (O+) ions at photon energies ranging from 29.9 to 46.0 eV (414.7 to 269.5 Å). All measurements were performed by merging an O+ beam with synchrotron radiation from an undulator beam line at the Advanced Light Source (ALS). At a resolution of 17 meV, more than 70 spectral features have been resolved, most of them identified and characterized.
K-shell photoabsorption of oxygen ions
Extensive calculations of the atomic data required for the spectral modelling of the K-shell photoabsorption of oxygen ions have been carried out in a multicode approach. The present level energies and wavelengths for the highly ionized species (electron occupancies 2 ≤ N ≤ 4) are accurate to within 0.5 eV and 0.02 A, respectively. For N > 4, lack of measurements, wide experimental scatter, and discrepancies among theoretical values are handicaps in reliable accuracy assessments. The radiative and Auger rates are expected to be accurate to 10% and 20%, respectively, except for transitions involving strongly mixed levels. Radiative and Auger dampings have been taken into account in the calculation of photoabsorption cross sections in the K-threshold region, leading to overlapping lorentzian shaped resonances of constant widths that cause edge smearing. The behavior of the improved opacities in this region has been studied with the xstar modelling code using simple constant density slab models, and is displayed for a range of ionization parameters.
The Astrophysical Journal, 2005
We present high resolution laboratory spectra of K-shell X-ray lines from inner-shell excited and ionized ions of oxygen, obtained with a reflection grating spectrometer on the electron beam ion trap (EBIT-I) at the Lawrence Livermore National Laboratory. Only with a multi-ion model including all major atomic collisional and radiative processes, are we able to identify the observed K-shell transitions of oxygen ions from O III to O VI. The wavelengths and associated errors for some of the strongest transitions are given, taking into account both the experimental and modeling uncertainties. The present data should be useful in identifying the absorption features present in astrophysical sources, such as active galactic nuclei and X-ray binaries. They are also useful in providing benchmarks for the testing of theoretical atomic structure calculations.
Photoionization of atomic oxygen at the multiplet term level from 20 to 212 eV
1995
The valence shell photoionization branching ratios of atomic oxygen are measured at the multiplet term level in a synchrotron-radiation-based electron spectrometry experiment and calculated using the multiconfiguration Hartree-Fock (MCHF) method for photon energies between 20 and 212 eV. The [2p](5, D, P) branching ratios, [2s] P to [2s] P intensity ratio, and [2s] to [2p] cross-section ratio for removal of a 2s or 2p electron are presented, and satisfactory agreement between the experiment and the MCHF calculation is found. In addition, the relative photoionization cross section is measured between 24 and 122 eV and is compared with calculations and a previous absolute cross-section measurement. Good agreement between the experimental and MCHF results is seen.
Physical Review A, 1999
Absolute cross sections for 2s-electron photoionization of atomic oxygen into the final ionic states O ϩ (2s Ϫ14 P e , 2 D e , 2 S e , 2 P e )and for the occupation of the O ϩ (3s 2,4 P e ) satellite states have been determined experimentally by photon-induced fluorescence spectroscopy. Comparison of the experimental results with theoretical predictions using multiconfiguration-interaction wavefunctions employing the ab initio R-matrix technique are made. Suitable harmony is seen only in the case of cross section ratios for 2s Ϫ1 removal or 3s-satellite excitation.
Influence of strongly coupled plasma environment on photoionization of H-like O7+ ion
Physics of Plasmas, 2021
The effect of strongly coupled plasma environment on the photoionization cross sections of the H-like O 7þ ion is studied within the framework of relativistic configuration interaction technique implemented in the flexible atomic code. The analytical b-potential of Li and Rosmej [Phys. Lett. A 384, 126478 (2020)] and uniform electron gas model potential of Saha and Fritzsche [J. Phys. B 40, 259 (2007)] have been employed for incorporating the plasma shielding effects. The level energies for unscreened H-like O 7þ ion are in excellent agreement with the National Institute of Standards and Technology values. The bound and continuum state wavefunctions are determined by solving the modified Dirac equations. The photoionization cross sections evaluated in the dipole approximation are obtained from the bound-free transition matrix element. Cross section calculations are performed over an electron density range of 1.0 Â 10 19-2.0 Â 10 23 cm À3 and a temperature range of 200-1000 eV. The plasma environment is found to considerably influence the photoionization cross sections. It has been observed that the ionization thresholds move to the low energy region with the increase in free electron densities. The present results will be beneficial for the interpretation of spectra observed in a variety of astrophysical and laboratory plasmas.