Ionization of molecular hydrogen by proton impact. I. Single ionization

Single-ionization cross sections of the proton-hydrogen molecule collision are calculated in semiclassical approximation by using atomic and Heitler-London-like two-center molecular wave functions for the ground state of ${\mathrm{H}}_2$. In transition matrix elements, calculated with two-center wave functions, the factors depending on ‖r-${\mathbf{R}}_0$/2‖ (${\mathbf{R}}_0$ is the vector of the molecular axis) are expanded into Legendre series. The calculated total and differential cross sections are compared to the measured data, and their dependence on target wave functions is discussed. The success of the simple approach, which uses twice the cross sections calculated for the hydrogen atom, is explained with the dominance of monopole contributions in the expansion in ${\mathbf{R}}_0$. While for homonuclear diatomic molecules the differential cross sections could be well described by the additivity rule, for other molecules the validity of such approaches is questionable.