Total and Excitation-Transfer Cross Sections for Collisions between2S3Metastable and Ground-State Helium Atoms

Abstract

Total and excitation-transfer cross sections for collisions between $2{}_{}{}^3{}_{}{}^{}S$ metastable and ground-state helium atoms have been calculated in the perturbed-stationary-state approximation, using the best available adiabatic ${}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ potential curves for ${\mathrm{He}}_2$, and in the "diabatic" approximation, using a repulsive ${}_{}{}^3{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ curve, constructed so as to have the appropriate united-atom limit. Both the total and excitation-transfer cross sections are found to show an oscillatory energy dependence. The detailed nature of these oscillations is found to be different for the adiabatic and "diabatic" descriptions. However, the average magnitude of the cross sections does not show this sensitivity. Differential cross sections have also been calculated and show considerable structure. Existing experimental measurements are included and compared with these calculations.