Theoretical Calculations of Electron Excitation of the Lowest Autoionization States of the Rb Atom

Abstract

Purpose. The value of the autoionization cross section and its energy dependence are determined to a great extent by excitation and subsequent electron decay of the lowest energy states. Recently, experimental data on the excitation cross sections of the rubidium atom lowest doublet (4p55s2)2P3/2,1/2 and quartet (4p54d5s)4P1/2,3/2,5/2 autoionizing states were obtained which promoted their theoretical investigations. Methods. Theoretical calculations were performed using the Flexible Atomic Code universal program package which takes account of the relativistic nature of the complex atoms excitation by the use of the Dirac-Coulomb Hamiltonian. The radial orbitals for basic relativistic wavefunctions were obtained by solving the Dirac-Fock-Slater equation. Results. Comparison of the experimental excitation cross sections for the doublet (4p55s2)2P3/2,1/2 and quartet (4p54d5s)4P1/2,3/2,5/2 autoionizing states with available theoretical data and our relativistic calculations is presented. The results of the study of the parameter R0 for the intensity ratio for the 2P3/2 and 2P1/2 states of the 4p55s2 configuration are presented. Our calculations in the distorted waves approximation is shown to well describe the experimental data in the energy region above 70 eV. At low collision energies our calculations qualitatively predict the presence of the threshold resonant excitation; however in the energy region 20-50 eV only the R-matrix method qualitatively describes the complex nature of excitation and decay of the lowest quartet autoionizing states of the rubidium atom. Conclusions. Electron excitation of the doublet (4p55s2)2P3/2,1/2 and quartet (4p54d5s)4P1/2,3/2,5/2 autoionizing states of the rubidium atom in the collision energy range from the excitation thresholds up to 700 eV was studied in the terms of the distorted waves relativistic approximation. A comprehensive analysis of the obtained results using the available experimental and theoretical data showed that the relativistic distorted waves approximation taking into account the configurational mixing is a suitable tool for describing the autoionizing states of the rubidium atom in a wide range of collision energies and allowed one to obtain the absolute values of the experimental excitation cross sections of the (4p55s2)2P3/2,1/2 and (4p54d5s)4P1/2,3/2,5/2 states.