Insights into the Formation of Hydroxyl Radicals with Nonthermal Vibrational Excitation in the Meinel Airglow.

To understand night time airglow in the Meinel bands and heat conversion from the highly excited OH radicals in the upper atmosphere via the important atmospheric reaction H + O3 → OH + O2, we report here a quasi-classical trajectory study of the reaction dynamics on a recently developed full-dimensional potential energy surface (PES). Our results indicate that the reaction energy of this highly exoergic reaction is almost exclusively channeled into the vibration of the OH product, underscoring an extreme departure from the statistical limit. The calculated OH vibrational distribution is highly inverted and peaks near the highest accessible vibrational state, in excellent agreement with experimental observations, validating the accuracy of the PES. More importantly, the dynamical origin of the nonthermal excitation of the OH vibrational mode is identified by its large projection onto the reaction coordinate at a small potential barrier in the entrance channel, which controls the energy flow into various degrees of freedom in the products.