Y. K. Ho

Photoionization of Li and Na in Debye plasma environments

A calculation of the photoionization cross sections is presented for alkali-metal atoms such as Li and Na in plasma environments. The computational scheme is based on the complex coordinate rotation method. A model potential formalism has been used to simplify the computational complexity of the problems of making quantitative predictions of properties and interactions of many electron systems in Debye plasmas. The plasma environment is found to appreciably influence the photoionization cross sections. In this regard the photoionization cross sections of isolated atoms are also discussed that is found to be in good agreement with the previous theoretical results. It is observed that the strong plasma screening effect remarkably alters the photoionization cross sections near the ionization threshold. The Cooper minimum in the photoionization cross sections of Na shifts toward the higher energy as the plasma screening effect increases. For Li, the Cooper minimum is uncovered in strong plasma environments. This is the first time such structures have been determined.

Ground states of helium in exponential-cosine-screened Coulomb potentials

Ground-state energies and wavefunctions for helium atom (He) in exponential-cosine-screened Coulomb potentials (ECSCP) with screening parameter λ, have been obtained for various values of λ within the framework of Ritzs variational principle. Highly correlated and extensive wavefunctions have been used to obtain energy eigenvalues. The ground-state energies of He for various values of λ have been shown to converge with the increase of the terms in the wavefunction. The ground-state energies of He+ along with the ionization potentials of He have also been reported. Our present work represents a first calculation, for the first time in the literature, of the ground-state energies of He interacting with ECSCP.

Electron affinity of the hydrogen atom and a resonance state of the hydrogen negative ion embedded in Debye plasmas

The 2s 21 S e autoionization resonance state of the hydrogen negative ion embedded in Debye plasmas is determined by calculating the density of resonance states using the stabilization method. The electron affinity of the hydrogen atom is also estimated for various Debye lengths.A screened Coulomb potential obtained from the Debye model is used to represent the interaction between the charged particles. A correlated wave function consisting of a generalized exponential expansion has been used to represent the correlation effect between the three charged particles. The screening effect is taken care of forallpairsofthechargedparticles.Thecalculatedresonanceenergiesandwidths for various Debye parameters ranging from infinity to a small value along with the electron affinity are reported.

Hydrogen atoms in Debye plasma environments

Plasma-screening effects are investigated on hydrogen atoms embedded in weakly coupled plasmas. In the present context, bound state wave functions are introduced related to the screening Coulomb potential (Debye model) using the Ritz variation method. The bound energies are derived from an energy equation, which contains one unknown variational parameter. To calculate the parameter numerically, fixed-point iteration scheme is used. The calculated energy eigenvalues for various Debye lengths agree well with the other available theoretical results. The radial wave functions and radial probability distribution functions are presented for different Debye lengths. The outcomes show that the plasma affects the embedded hydrogen atom.

Influence of plasma environments on photoionization of atoms

Within the framework of the method of the complex-coordinate rotation, a computational scheme has been developed to investigate influence of plasma environments on photoionization for atoms and ionized atoms. The Debye screening potential is used to describe effects of the plasma environments. Photoionization cross sections are reported for hydrogen and hydrogen-like helium in the ground states and compared with the available data. Investigation shows that near the ionization thresholds, photoionization is sensitive to the plasma screening. The strong screening remarkably alters the photoionization cross sections near the ionization thresholds. It is concluded that a great error may arise if photoionization cross sections for isolated atoms or ions are employed for numerical simulations of astrophysical and laboratory plasmas.

Investigation of charge transfer and ionization in He-like systems (Li+, Be2+, B3+, C4+, N5+, O6+)-hydrogen atom collisions in Debye plasmas

The charge transfer and ionization cross sections have been calculated for He-like system (Li+, Be2+, B3+, C4+, N5+, O6+) and hydrogen atom collisions in Debye plasmas for energies ranging from 1 to 500 keV using the classical trajectory Monte Carlo method. Interactions of the active electrons with the projectile ions have been described by model potentials. Cross sections are determined in both screening and unscreening environments, and a comparative study between both environments has been carried out. In particular, an interesting feature of sudden increase in the ionization cross sections at lower velocities is also observed in all the systems like pandey et al. [M. K. Pandey et al., Phys. Plasmas 19, 062104 (2012)] calculations for O8+ + H collision. The feature of sudden increase in ionization cross sections at lower velocities and the effect of plasmas condition on it are explained in terms of the classical trajectory framework. We have found the cross sections for both capture and ionization are ...

Cross sections of charge exchange and ionization in O8+ +H collision in Debye plasmas

Charge exchange and ionization processes in O8+ +H collision system in a Debye plasma are studied using the classical trajectory Monte Carlo (CTMC) method in the collision energy ranging from 1 keV/amu to 500 keV/amu. Total charge exchange and ionization cross sections have been determined in both screening and unscreening environments. In the unscreened case, partial cross sections for transfer into individual n shells of the projectile have also been determined. An interesting and remarkable feature of sudden increase in the ionization cross sections at lower velocities is discussed in terms of the CTMC framework. Results are analyzed in light of available theoretical and experimental results. The cross sections dependencies on Debye screening lengths have been investigated, and plasma screening effect on charge exchange and ionization cross sections has been found throughout the collision energies range, but is particularly pronounced at low projectile collision energies. The sudden rise in the ionizat...

Combined effect of Debye plasma environment and external electric field on hydrogen atom

We consider weakly coupled plasmas, characterized by Debye-Huckel model potential, and an external electric field along z-axis. Due to plasma environment the energy levels of atom are shifted up, bound states are merged to continuum. For external electric field the excited energy levels also split up; degenerate energy eigenvalues become nondegenerate. In the presence of external electric field, energy levels are shifted up and down, except ground state. The ground state energy value is shifted only down. Therefore, it is very interesting to study the combined effect of plasmas and external electric field on a simple atom (hydrogen). To calculate the energy levels and the corresponding states, we expand the wave function in terms of linear combination of the basis functions. The basis is generated by hydrogenic wave functions. Here, we estimate various plasma surroundings and electric field strengths. We observe converged results for the basis size 45, with angular momentum states up to eight.

S-wave resonances in e + -He scattering below the Ps (n = 2) excitation threshold

Two S-wave resonances in the positron–helium system are calculated using the stabilization method. A model potential for helium is used to represent the He+ ion core and the outer electron. Hylleraas-type wavefunctions are used to represent the correlation effects between the outer electron, the positron and the He+ core. Resonance energies and widths for two resonances lying below the Ps (n = 2) threshold are reported.

One- and two-photon ionization of hydrogen atom embedded in Debye plasmas

We present a detailed analysis of the plasma-induced resonance-like atomic structures near the ionization threshold in one- and two-photon ionization of hydrogen atom. Such resonance-like structures result from the migration of the upper bound excited states of bound-bound atomic transitions into the continuum due to the less attractive screened Coulomb potential which simulates the external environmental effect for an atom embedded in Debye plasma. The change from the resonance-like narrow structures into broad continuous spectra as the plasma effect increases could be accounted for by the overlap between the respective wavefunctions of the atomic electron in the initial state and its corresponding outgoing ionized state in the continuum.