Ionization of the quasimolecule HeH2+ formed in He+–H2 collisions

Abstract

Ionization processes in He+–H2 collisions have been studied in the ion energy range of 2–10 keV using electron spectroscopy. Quasimolecular autoionization and direct ionization due to superpromotion of the diabatic term were found to dominate at lower (<5 keV) and higher (>5 keV) ion energies of the range under study, respectively. The parameters of the diabatic quasimolecular term responsible for direct ionization were deduced from the experimental data by solving the ‘inverse problem’, and the following features of this channel have been revealed: (i) it proceeds via intermediate resonant two-electron rearrangement: 1a′(2a′)2 → (1a′)23a′; (ii) in the subsequent superpromotion of the outer electron, the incident ion forms a quasimolecule with only one of the atoms of the target molecule. Apart from the structure associated with autoionization transitions in the helium atom, a structure associated with the decay of autoionization states of a hydrogen molecule was revealed, and the relevant energies, widths and line profiles were determined.