INTERNAL AND TRANSLATIONAL ENERGY EFFECTS ON THE CHARGE-TRANSFER REACTION OF CO2+ WITH O2

We have investigated the reaction of CO2+ with O2 over a range of kinetic energies with a guided ion beam apparatus and over a range of temperatures and kinetic energies with a variable-temperature selected-ion flow drift tube. The rate constants decrease with increasing kinetic energy at low energy and increase at higher energy. Below about 10 eV, reaction proceeds by charge transfer only. Above 10 eV, O+ and CO+ product ions are observed in addition to the charge-transfer channel. At low energy, i.e. below 0.1 eV, the rate constants at a particular center-of-mass kinetic energy, [KE(cm)], do not depend on the temperature of the buffer gas. This indicates that energy in rotations and in the bending vibrational modes does not play a major role in determining reactivity. Above 0.1 eV, the rate constants at a particular [KE(cm)] do depend on temperature, such that the higher the buffer gas temperature the larger the rate constants. Analysis of the data suggests that the enhancement observed with temperature is primarily due to excitation of the CO2+ stretching vibrational modes. The analysis indicates that excitation of the CO2+ stretching modes increases the rate constant by approximately an order of magnitude. Excitation of bending vibrations may also enhance the efficiency of charge transfer above 0.2 eV. Translational energy causes a small increase in the charge-transfer rate constant above 0.3 eV.