Kinetic energy dependence of the branching ratios of the reaction of N ⁺ ions with O₂

The kinetic energy dependence of the branching ratios of the reaction of N⁺ with O₂ has been determined in the collision energy range from 0.06 to 1.8 eV using a selected-ion flow-drift tube. At energies near thermal, the branching ratios were found to be the following percentages: O₂⁺ 51±4, NO⁺ 43±4, and O ⁺ 6±4, in good agreement with the results of some of the earlier thermal-energy studies. At relative kinetic energies above about 0.1 eV, the O₂⁺ channel increases and eventually becomes dominant, at the expense of the NO⁺ channel. At the highest energy investigated in the present study, the branching ratios obtained are 79%, 19%, and 2%, respectively, and join rather smoothly with crossed-beam data extending to higher energies. The O⁺ channel remains a minor channel over the energy range studied here. These energy-dependent branching ratios are in striking contrast to the total rate constant for this reaction, which is virtually energy-independent for energies below 1 eV.