AB-INITIO POTENTIAL-ENERGY SURFACES AND ELECTRON-SPIN-EXCHANGE CROSS-SECTIONS FOR H-O-2 INTERACTIONS

Accurate quartet- and doublet-state potential-energy surfaces for the interaction of a hydrogen atom and an oxygen molecule in their ground states have been determined from an ab initio calculation using large- basis sets and the internally contracted multireference configuration interaction method. These potential surfaces have been used to calcula te the H-O-2 electron-spin-exchange cross section; the square root of the cross section (in no), not taking into account inelastic effects, can be obtained approximately from the expressions 2.390E(-1/6) and 5. 266-0.708 log(10)(E) at low and high collision energies E (in E(h)), r espectively. These functional forms, as well as the oscillatory struct ure of the cross section found at high energies, are expected from the nature of the interaction energy. The mean cross section (the cross s ection averaged over a Maxwellian velocity distribution) agrees reason ably well with the results of measurements.