Molecular-state treatment of electron capture in collisions of ions with He atoms below

Abstract

Cross sections of electron-capture processes are calculated by using a molecular-state expansion method in collisions of ions with helium atoms. Semiclassical and quantum-mechanical close-coupling equations with ten molecular channels for the former and with three channels for the latter are solved numerically at collision energies from to and from to , respectively, to obtain scattering amplitude. The total cross sections for the triplet ion formation have a broad maximum at about and decrease below, reaching a minimum around . But they begin to increase again below . At collision energies lower than the contribution of the state to the electron-capture process is found to be larger than that of the state, but at intermediate collision energies between and the order of the contributions from these two states reverses. The total cross sections for the singlet ion formation have a broad minimum at about and they increase monotonically with decreasing collision energy. At most of the collision energies studied here, the contribution of the state is found to be dominant. In both triplet and singlet ion formation, at lower collision energies below , the cross sections begin to increase rapidly with decreasing collision energy due to an orbiting effect, and several resonance-type peaks are also seen. The position of these resonances can be assigned with the rovibrational level of a quasimolecule formed during collision.