Impact-Parameter Treatment of Hydrogen-Hydrogen Excitation Collisions. II. Four-State Approximation

Abstract

An impact-parameter treatment is carried out for the processes $\mathrm{H}\mathrm{}\left(1s\right)+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}\to \mathrm{H}\mathrm{}\left(1s\right)+\mathrm{H}(2s or 2p)$ with incident hydrogen-atom energies $E$ in the range $360 \mathrm{eV}<~E<~100 \mathrm{keV}$. Full account is taken of distortion, back coupling, rotational coupling, and the virtual transition sequence $1s\rightleftharpoons 2p\rightleftharpoons 2s$. Comparison with previous two-state calculations, which included only the effects of distortion and back coupling, shows that the presence of the optically allowed $1s-2p$ transition increases the $1s-2s$ cross section at all energies, augmenting it by as much as 73% at 360 eV, and contributes relatively less with energy increase. For excitation of the $2p$-magnetic components, rotational coupling and the inclusion of the optically forbidden channel influence the cross sections only slightly and in opposite senses for energies above 6 keV, while for lower energies their combined effect is to decrease severely the excitation probabilities. The percentage polarization of the emitted radiation is also evaluated.