ELECTRON-CAPTURE BY STATE-SELECTED O(2-HYDROGEN() IONS FROM ATOMIC)

Ab initio methods are used to obtain the adiabatic potential energies and the corresponding non-adiabatic radial and rotational coupling mat rix elements for all of the doublet and quartet SIGMA, PI and DELTA st ates of OH2+ which contribute to electron capture by state-selected O2 + from atomic H. Semiclassical methods are used to treat the collision dynamics. Results are presented both for ground (3P) and metastable ( 1D, S-1) state ions in the range of collision energies from 20 eV to 3 0 keV. The cross sections for electron capture by ground state ions ar e about a factor of three larger than for metastable ions over a very wide energy range. The effect of rotational mixing of the 4SIGMA- and 4PI states in the entry channel for ground state ions is found to be l arge at energies in excess of a few 100 eV. The results are in excelle nt agreement with the experimental energy gain spectra.