Calculation of the photoionization cross sections for the ions of the rubidium isoelectronic sequence by the Dirac-Fock method

The photoionization cross sections for the ground and some excited states of 11 ions of the rubidium isoelectronic sequence from Rb through Ag¹⁰⁺ are calculated by the relativistic Dirac-Fock self-consistent field method. The energy dependence of the photoionization cross sections and the changes in the threshold values along the isoelectronic sequence are considered. The influence of the exchange effect and the choice of gauge on the calculated values of photoionization cross sections is examined. For practical use, the calculated cross sections are approximated by an analytical expression. Along with the total photoionization cross sections, the asymmetry parameter in the angular distribution of photoelectrons and the degree of their polarization are also calculated.     

Calculation of atomic and molecular photoionization cross sections using the ground state inversion potential method

Calculations of atomic photoionization cross sections to near Hartree-Fock accuracy can be achieved very simply if the non-local Hartree-Fock potential experienced by the photoelectron is replaced by a local potential obtained by inversion of the corresponding ground state orbital. Subshell cross sections for atomic photoionizatim for representative atoms in the range 0–1500 eV calculated in this way are in good general agreement with Hartree-Fock values and with experiment. The extension to molecular systems and the use of an independent atomic centre approach to calculation of molecular photoionization cross sections at low photon energies is outlined.     

Calculation of the photoionization with deexcitation cross sections of He and helium-like ions

We discuss the results of the calculation of the photoionization with deexcitation of excited He and helium-like ions Li⁺ and B³⁺ at high but nonrelativistic photon energies θ. Several lower ¹ S and ³ S states are considered. We present and analyze the ratios R _d ⁺ * of the cross sections of photoionization with deexcitation, σ _(d) ⁺ *(θ), and of the photoionization with excitation, σ⁺*(θ). The dependence of R _d ⁺ * on the excitation of the target object and the charge of its nucleus is presented. In addition to theoretical interest, the results obtained can be verified using long-lived excited states such as 2³ S of He. The text was submitted by authors in English.     

X-ray photoionization cross sections for quantitative analysis

The relative photoemission intensities from subshells of 51 elements and simple compounds have been measured using X-ray photoelectron spectroscopy. The chemical composition of each specimen surface was monitored by Auger electron spectroscopy and contamination was minimized by Ar⁺ ion bombardment. Experimental photoelectron cross sections derived for MgKα (1254 eV) radiation were compared with theoretical Hartree-Slater subshell photoionization cross sections calculated by Scofield. Good correlation (r = 0.96) between theory and experiment was observed over two orders of magnitude for most of the elements studied. Relative cross sections for subshells of a given element are also consistent with theoretical values, with several notable exceptions. The results indicate that quantitative analysis of ESCA spectra is possible using the Scofield cross sections.     

Vibrationally resolved K-shell photoionization cross sections of methane

We use an extension of the static-exchange density functional theory (DFT) method, previously reported in [E. Plésiat et al., Phys. Rev. A 2, 023409 (2012), E. Plésiat, P. Decleva, F. Martín, Phys. Chem. Chem. Phys. 31, 10853 (2012)], to evaluate vibrationally resolved (total and angular) K-shell photoelectron cross sections of methane. The calculated cross sections are in very good agreement with the existing experimental measurements at low photoelectron energies. We show that, in contrast with the rich interference patterns previously observed in molecular frame C(1s) photoelectron angular distributions of methane at both low and high photoelectron energy, no interference effects are observed in the calculated β parameters, even at high photon energies.     

原子光电离过程中的Cooper最小

利用Dirac-Slater相对论自洽场理论,研究了入射光子能量较小时Na和K原子最外壳层电子的光电离截面的变化规律及其s和p壳层的Cooper最小,在论述Cooper最小的产生原因及其基本特征的基础上,分析了影响Cooper最小的主要因素原子实、主量子数、角量子数以及总量子数等,并对这种影响进行了较为详细的理论说明.     

The computation of photoionization cross sections by means of the scaled Thomas-Fermi potential

Photoionization cross sections of lighter neutral elements (Na, K, Mg, C, N, O) have been calculated by means of the scaled Thomas-Fermi potential and compared with results obtained by other methods. In contrast to the quantum-defect method, the present method is applicable and yields reasonable results also for ultraviolet transitions, that is, for electron energies up to several Rydbergs and for low-lying bound states with large quantum defect.     

An atomic diffraction theory of molecular photoionization cross sections

A theory of molecular photoionization cross sections is developed on the basis of locally atomic character of the one-electron final state in the Golden Rule expression for the molecular orbital cross section. Ionization amplitudes from several atomic centres are added and rotationally averaged to produce molecular orbital cross sections displaying a sum of pseudo-atomic cross sections weighted according to the LCAO composition of the orbital and also two-centre products reflecting interference effects. The atomic ionization amplitudes are obtained by use of an atomic central potential constructed by an inversion procedure from the form of the ground state orbital. The theory is of a simple chemical nature but usually of at least semi-quantitative accuracy. In this work we illustrate the nature of the two-centre interference effects in small diatomic molecules (H₂, HF, N₂).     

Orthogonalized-plane-wave approximation in the calculation of photoionization cross sections of molecules

The physical bases of the OPW approximation in the calculation of molecular photoionization cross sections are considered in terms of the scattering theory, and the ways of improving the calculation within the framework of OPW approximation are discussed.Numerical calculations are done on several molecules by the ordinary OPW method and by its modifications using the bound orbitals obtained by ab initio SCFMO calculations with gaussian basis set.     

Triple differential cross sections for the double photoionization of H2

Triple differential cross sections arising from the break up of the H2 molecule by a single photon are presented. The time-dependent close-coupling technique is used to calculate differential cross sections for various geometries. Excellent agreement is found between current work and recent exterior complex-scaling calculations, confirming, for the first time, the absolute magnitude of the triple differential cross sections. Our calculations also compare favorably with recent synchrotron light source measurements.     

Resonant and near-threshold photoionization cross sections of Fe14+

Photoionization (PI) of Fe14+ in the range from 450 to 1100 eV was measured at the BESSY II storage ring using an electron beam ion trap achieving high target-ion area densities of 10(10) cm(-2). Photoabsorption by this ion is observed in astrophysical spectra and plasmas, but until now cross sections and resonance energies could only be provided by calculations. We reach a resolving power E/ΔE of at least 6500, outstanding in the present energy range, which enables benchmarking and improving the most advanced theories for PI of ions in high charge states.     

Comment on measuring photoionization cross sections of excited atomic states

The results of the measured absolute photoionization cross section from the 7² P excited states of cesium are reported. The following values have been obtained: (6.2±0.5)×10⁻¹⁸ cm² and (8.8±1.6)×10⁻¹⁸ cm² for the levels 7² P _1/2 and 7² P _3/2, respectively.     

Chemical shift resolved photoionization cross sections of amorphous carbon nitride

We present a method to derive an upper bound for the entropy density of coupled map lattices with local interactions from local observations. To do this, we use an embedding technique that is a combination of time delay and spatial embedding. This embedding allows us to identify the local character of the equations of motion. Based on this method we present an approximate estimate of the entropy density by the correlation integral.     

锂原子光电离截面的无穷阶计算

利用多体微扰理论,把基态锂原子K和L壳层电子的光电离过程中的电子相关效应计算到了无穷阶。用Feynman图技术讨论了基态关联效应和混相近似效应,并计算了与无穷阶末态关联的耦合效应。计算结果与实验和其他理论结果吻合得很好。     

Calculation of the ratio of isomeric cross sections

A new, more rigorous method for calculating the ratio of isomeric cross sections has been developed. The method is particularly valuable when the energy and spin distribution are known before the gamma rays populating the isomeric and ground states start to cascade. The usefulness of the method was demonstrated by applying it to the analysis of the ratio of isomeric cross sections in the ¹⁹⁶Hg(n,γ)¹⁹⁷Hg reaction, which was initiated by thermal neutrons.     

Fits to new calculations of photoionization cross sections for low-Z elements

Analytical approximations to results of new calculations of partial (i.e. by subshell) photoionization cross sections of elements (2 < Z < 30, Z = 36) are presented which cover the photon energy range from near threshold to 300 keV. The computer program developed by Brysk and Zerby, which is based on the single-electron model and uses screened self-consistent field and Dirac-Slater wave function data furnished by Cromer, Waber and Liberman, was used. Sufficient multipoles were included to calculate the partial cross sections within a few per cent, on the assumed model. Results for several elements are compared with other calculations and measurements of total photoionization cross sections. The results are presented in a form most convenient for calculations of opacities of hot gases.     

Sm和U原子光电离截面的模型势计算

本文给出了使用四种不同形式的势对Sm基态光学电子所属壳层光电离截面计算的结果,同时给出了U原子三个激发态参量形式的极化修正模型势光电离截面的计算结果.我们的结果与其他作者使用相同形式的势计算的结果较好地符合.使用参数形式的极化模型势计算光电离截面是一种有效的方法.     

Calculation of the cross sections for the photoionization of H2 and D2 into different vibrational states of the ion

The dependence of the electronic transition moment on the internuclear distance is explicitly taken into account in the calculation of the photoionization cross section. Thus, the partial ionization cross sections for producing different vibrational states of the residual ion are obtained without invoking the Franck-Condon factor approximation. The exact electrostatic potential of H₂⁺, as well as the two-center Coulomb field, is used in the evaluation of the continuum wave function. The result can explain fairly well the ratios of the partial cross sections measured at 584 Å. The effect of the polarization of H₂⁺ due to the departing photoelectron is also studied and found to be small as far as the relative cross section is concerned. The total photoionization cross sections of H₂ and D₂ are compared with previous results obtained by other authors.     

Calculation of cross sections for elastic electron-molecule collisions

The phase functions and the partial and total elastic scattering cross sections for electrons with energies from 0.23 to 14.46 eV are numerically calculated on a computer for nitrogen and oxygen molecules. The phase equation in spheroidal coordinates is employed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 104–107, May, 1976.