Alignment and orientation of the excited H(2p) orbital following H+He collisions at intermediate energies

A systematic theoretical study of alignment and orientation of the excited H(2p) orbital in H+He collisions in the energy range from 0.8 to 8 keV is carried out with use of a molecular-orbital representation. The present model takes the active electron in the H atom explicitly into account, while treating the He atom as a frozen core. Calculated alignment and orientation agree very well with recent measurements, implying that the dominant excitation mechanism for H(2p) excitation is the strong X ²A ²Σ radial coupling for all energies studied. Hence, the integral alignment A₂₀ is negative and slowly varying with energy. Present partial excitation cross sections for H(2s) and H(2p) agree well with the corresponding measurements, except at energies below 1--2 keV.