Kinetic energy dependence of C +( 2P) + O 2 from thermal energies to 35 eV c.m.

Abstract

Guided ion beam mass spectrometry is used to examine the kinetic energy dependence of the reaction of ground-state atomic carbon ion with molecular oxygen. At the lowest energy examined, 0.05 eV, the magnitude of the total cross-section approaches to within 75% of the prediction of the Langevin—Gioumousis—Stevenson (LGS) model. The branching ratio at this energy is 60% (O + + CO) and 40% (CO + + O). These results are in good agreement with previous studies at thermal energies. As the energy is increased, σ total falls more rapidly than the LGS model and the fraction of O + formed declines steadily such that, above 0.14 eV, CO + + O is the preferred product channel. There is no indication of direct competition between these two reaction channels. Results of phase space calculations indicate that the formation of CO + is largely statistical but production of O + is highly non-statistical. The endothermic charge transfer channel, O + 2 + C, is also observed at elevated energies. Analysis of the cross-section data for this product yields a threshold energy of 0.82 eV, in excellent agreement with the known thermochemistry. The mechanism of these reactions is discussed in the context of qualitative potential energy surfaces.