Dynamics of vibrational energy excitation and dissociation in oxygen from direct molecular simulation

We present a molecular level study of vibrational excitation and non-equilibrium dissociation of diatomic oxygen due to O₂ + O interactions. O₂ + O interactions are modeled using nine potential energy surfaces corresponding to 1¹A^′, 2¹A^′, 1¹A^′′, 1³A^′, 2³A^′, 1³A^′′ 1⁵A^′, 2⁵A^′ and 1⁵A^′′ states, which govern electronically adiabatic collisions of ground-electronic-state collisions of diatomic oxygen with atomic oxygen. Characteristic vibrational excitation times are calculated over a temperature range of T = 3000 K to T = 15000 K. We observe that the characteristic vibrational excitation time for O₂ + O interactions is weakly dependent on temperature and increases slightly with increasing temperature. Vibrational excitation is slowest for interactions in the quintet spin state, with the 1⁵A^′′ state having the slowest excitation rate, and vibrational excitation is fastest on the 1¹A^′ potential energy surface. Dissociation rate coefficients in the quasi-steady state agree well with experimental data. Furthermore, dissociation during the quasi-steady state is found to be three times faster when O₂ + O interactions are included, compared to simulations including only O₂ + O₂ interactions.