Y. Wu

The generalized oscillator strengths of hydrogenlike ions in Debye plasmas

Plasma screening effects on the high-energy electron-impact excitation of hydrogenlike ions are investigated under the first Born approximation. The screening interactions are described by the Debye–Huckel model, and the wave functions are calculated numerically in a symplectic scheme. The generalized oscillator strengths (GOS) for transitions between the principal quantum number n⩽3 bound states are presented, and as an example, the scaled differential cross sections and total cross sections for 1s→2s and 2p and 2s→2p transitions are also given. It is found that the plasma screening interactions reduce the GOS for transitions between the states with different n and increase the GOS between the states with same n. The differential and total cross sections are decreased as the screening interactions increase.

Photoionization of Li and radiative recombination of Li+ in Debye plasmas

The photoionization cross sections in the photoelectron energy below 2 Ry are calculated for the ground and n≤4 excited states of Li embedded in plasma environments and the radiative-recombination (RR) rate coefficients for Li+ were presented for temperature T=100–32u2009000u2002K in a wide range of plasma parameters. The plasma screening interaction is described by the Debye–Huckel model and the energy levels and wave functions including both the bound and continuum states are calculated by solving the Schrodinger equation numerically in a symplectic integration scheme. The screening of Coulomb interactions remarkably changes the photoionization cross sections near the ionization threshold, and especially for the ns states, the Cooper minimum is uncovered and shifted to the higher energy as the screening interaction increases. The RR rate coefficients at low temperature have a complex variation on the Debye lengths; whereas at higher temperature the RR rate coefficients decrease with the increasing of screening ...

Theoretical investigation of total and state-dependent charge exchange in O6 + collisions with atomic hydrogen

The charge exchange process has been found to play a dominant role in the production of x-rays and/or extreme ultraviolet photons emitted from cometary and planetary atmospheres and from the heliosphere. Charge exchange cross sections, especially state-selective cross sections, are necessary parameters in simulations of this x-ray emission. In this study, charge exchange, or single-electron capture, due to collisions of ground state O6 +(1s2 1S) with atomic hydrogen has been investigated theoretically using the quantum-mechanical molecular-orbital close-coupling method (QMOCC). The multi-reference single- and double-excitation configuration interaction approach has been applied to compute the adiabatic potentials and nonadiabatic couplings, and the atomic basis sets used have been optimized with a method proposed previously to obtain accurate descriptions of the high-lying Rydberg states of highly charged ions. Total and final-state-selective cross sections are calculated for energies between 0.1 eV/u and 10 keV/u. The QMOCC results are compared to available experimental and theoretical data as well as to new atomic-orbital close-coupling (AOCC) and classical trajectory Monte Carlo (CTMC) calculations. A recommended set of cross sections, based on the QMOCC, AOCC and CTMC calculations, and existing data, are deduced which should aid in x-ray emission modelling studies.

Low-energy charge transfer in collisions of He2+ with H in a Debye plasma

Charge transfer in collisions of {alpha} particles with ground-state H embedded in a Debye plasma is studied in the low-energy region from 10{sup -4} eV to 5 keV. The screened Coulomb interaction is described by the Debye-Hueckel potential. The relevant molecular potentials and coupling matrix elements are obtained using a modified multireference single-and double-excitation configuration interaction package. Total and state-selective cross sections in the nonradiative charge-transfer collisions from 60 eV to 5 keV are calculated using the quantum-mechanical molecular-orbital close-coupling method. Both optical-potential and semiclassical methods have been used in the investigation of the radiative charge transfer from 10{sup -4} to 1 eV and 1 to 10{sup 2} eV, respectively. The total cross sections for the no-screening case are in good agreement with the existing data. The effects of the screened Coulomb potential on the electron-capture cross sections are discussed.

Adjustment of Born-Oppenheimer electronic wave functions to simplify close coupling calculations

Technical problems connected with use of the Born‐Oppenheimer clamped‐nuclei approximation to generate electronic wave functions, potential energy surfaces (PES), and associated properties are discussed. A computational procedure for adjusting the phases of the wave functions, as well as their order when potential crossings occur, is presented which is based on the calculation of overlaps between sets of molecular orbitals and configuration interaction eigenfunctions obtained at neighboring nuclear conformations. This approach has significant advantages for theoretical treatments describing atomic collisions and photo‐dissociation processes by means of ab initio PES, electronic transition moments, and nonadiabatic radial and rotational coupling matrix elements. It ensures that the electronic wave functions are continuous over the entire range of nuclear conformations considered, thereby greatly simplifying the process of obtaining the above quantities from the results of single‐point Born‐Oppenheimer calculations. The overlap results are also used to define a diabatic transformation of the wave functions obtained for conical intersections that greatly simplifies the computation of off‐diagonal matrix elements by eliminating the need for complex phase factors.