Abstract
A theory describing collisions between arbitrary atoms or ions and atomic hydrogen is developed. Results are obtained in terms of amplitudes for electron-hydrogen and proton-hydrogen collisions and the arbitrary atom or ion transition form factor. No recourse to scattering by fictitious electron-plus-proton atoms is necessary. Applications are made to the differential and total cross sections for He+(1s)+H(1s)He+(1s)+H(n=2). Agreement with recent measurements is obtained. A simple approximation to the results, σσpH(1sn=2)+8σpH(1s2s), is obtained and is in fair agreement with recent data.