Electronic Transitions in Slow Collisions of Atoms and Molecules. IV. Multistate Eikonal Approximation for Quasiadiabatic Transitions

Abstract

The coupled equations of the adiabatic-state expansion method for quasiadiabatic transitions in atomic collisions are reduced in the eikonal approximations to a form that allows straightforward computation. The multistate eikonal approximation is then applied to the ${\mathrm{He}}^{+}\mathrm{}\left(1s\right)+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}\to {\mathrm{He}}^{+}\mathrm{}\left(1s\right)+\mathrm{H}\mathrm{}\left(2p\right)\mathrm{}$ excitation process. The partial and total $2p$-excitation cross sections as well as the polarization of the light emitted by the excited H atoms are calculated. Our results compare well with recent experimental measurements. The importance of final-state coupling is dramatically illustrated by the above $2p$-excitation process. The qualitative features of the nonadiabatic effects are also investigated in the eikonal Born approximation as functions of the position and distance of closest approach of the two adiabatic states.