Electron capture and excitation in collisions of O+(4S,2D,2P) ions with He atoms and He+ ions with O atoms at energies below 10 keV.

Abstract

Electron capture and excitation in O[sup +]([sup 4][ital S],[sup 2][ital D],[sup 2][ital P])+He collisions above 100 eV are studied theoretically by using a semiclassical molecular representation and electron capture in He[sup +]+O([sup 3][ital P]) collisions; excitation and deexcitation in O[sup +]([sup 4][ital S])+He[leftrightarrow]O[sup +]([sup 2][ital D])+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[sup +]([sup 2][ital D],[sup 2][ital P]) ions to electron capture is much larger than that from the ground O[sup +]([sup 4][ital S]) ions. At energies below 1 eV, the cross section for electron capture in He[sup +]+O collisions is very small, with a magnitude of less than 10[sup [minus]20] cm[sup 2]. The cross sections for the excitation-deexcitation of metastable O[sup +] ions are larger, with values near 10[sup [minus]18] cm[sup 2].