Molecular treatment ofHe++H collisions

Abstract

Total cross sections for the reactions /sup 4/He/sup +/(1s)+H(1s)..-->../sup 4/He/sup +/(1s)+H(2p), /sup 4/He/sup +/(1s) + H(1s)..-->../sup 4/He(1s2p /sup 1,3/P)+H/sup +/ are calculated in an impact-parameter formalism, for collision energies 0.5--30 keV, using a molecular approach. The molecular energies are calculated at large internuclear distances by a configuration-interaction method, and at short distances by a block-diagonalization method. The radial couplings between the molecular wave functions are evaluated exactly, and turn out to depend strongly on the choice of origin of electronic coordinates; as a consequence, the cross sections also depend on this choice. The effect of the anomalous rotational couplings which decrease like R/sup -1/ is shown to be negligible, and a method to integrate them is proposed in the Appendix. Choosing the center of mass as origin of electronic coordinates, we obtain good agreement with experimental data, but we find no a priori reason to favor this choice. As an important conclusion, the main effect of the so-called momentum-transfer problem, which is the origin dependence of the cross sections, is due to the form of the molecular wave functions at short internuclear distances.