ELECTRON-CAPTURE AND EXCITATION IN COLLISIONS OF O+(S-4,D-2,P-2) IONS WITH HE ATOMS AND HE+ IONS WITH O-ATOMS AT ENERGIES BELOW 10-KEV

Electron capture and excitation in O+(4S,2D,2P)+He collisions above 100 eV are studied theoretically by using a semiclassical molecular representation and electron capture in He++O(3P) collisions; excitation and deexcitation in O+(4S)+HeO+(2D)+He collisions at lower energies are studied by using a fully-quantum-mechanical molecular representation. At higher energies, nonadiabatic couplings are the driving forces that cause transitions. At collision energies below 10 eV, transitions are driven by spin-orbit couplings. At kilo-electron-volt energies, the contribution from metastable O+(2D,2P) ions to electron capture is much larger than that from the ground O+(4S) ions. At energies below 1 eV, the cross section for electron capture in He++O collisions is very small, with a magnitude of less than 10-20 cm2. The cross sections for the excitation-deexcitation of metastable O+ ions are larger, with values near 10-18 cm2. © 1994 The American Physical Society.