A distorted wave method applied to study the 23S and 23P excitation of Helium atom by electron impact

Abstract

Electron scattering by atoms and molecules has attracted considerable attention since the earliest days of quantum mechanics. This is because they form the basis of understanding of many experimental techniques in physics, for example Rutherford back scattering and atomic and molecular spectroscopy. Due to the demand for atomic collision data set in various fields of physics various experimental techniques and theoretical approaches have been developed. In this study the distorted wave method has been applied to calculate the differential and integral cross sections for 11S_23Sand 11S_23Pexcitations of helium atom by electron impact in the energy range of 40-200 eV. The initial distortion potential was taken as the static potential of the helium (target) atom in the initial state (lIS) while the fmal distortion potential was taken as the average of the initial- and final-state static potentials of helium atom. The distorted waves were determined by partial wave expansion method by expanding them in terms of spherical harmonics while the radial equation corresponding to distorted waves was evaluated using Numerov method. A computer program DWBAI written for e-H scattering by Madison and Bartschat was modified to perform the numerical calculations for e'-He scattering and the results for differential and total cross section were calculated and compared with experimental and theoretical results. The present distorted wave method results for 23p at all incident energies except for 40 eV compared well with most of the experimental and theoretical results than in the case of 23S where the agreement was good at lower scattering angles except for 200 eV. , Therefore we can conclude that the present distorted wave method worked for well for excitations. However it worked better for 11S_23P transition than in the case of 11S_23S transition.