TEMPERATURE, KINETIC-ENERGY, AND INTERNAL ENERGY DEPENDENCES OF THE RATE-CONSTANT AND BRANCHING FRACTION FOR THE REACTION OF O+ (S-4) WITH CO2

Rate constants and branching fractions were measured for the reaction of O+ (4S) with CO2 as a function of average ion-neutral center-of-mass kinetic energy (<KE(cm)>) at several temperatures. The reaction produces both O2+ and CO2+ as product ions. The total rate constants were found to be nearly collisional at low <KE(cm)> and to decrease slightly at higher <KE(cm)>. No temperature dependence of the rate constants was found at any given <KE(cm)>, indicating that neither CO2 rotational excitation nor CO2 bending mode excitation has much effect on the overall reactivity. In contrast, the branching fraction for the endothermic charge transfer channel leading to CO2+ was found to increase with increasing <KE(cm)> and also to increase with temperature at fixed <KE(cm)>. Analysis of the data indicates that the branching fraction depends on the total energy in the system (electronic, kinetic, rotational, and vibrational).