Determination of the collisional energy transfer distribution responsible for the collision-induced dissociation of NO2 with Ar

Abstract

Collisional energy transfer is an essential aspect of chemical reactivity and maintenance of thermal equilibrium. Here we report the shape (energy-dependence) of the collisional energy transfer probability function for collisions of vibrationally excited NO2 entrained in a molecular beam and photoexcited to within 40cm−1 of its dissociation threshold. The internally excited molecules undergo collisions with Ar atoms in a crossed beam apparatus. Dissociative collisions rapidly produce the NO(J) fragment, which is observed by velocity-mapped ion imaging and REMPI techniques. The measured collisional energy transfer function is obtained via energy conservation and is compared with the results of classical trajectory calculations. Good agreement between the theory and experiment is found for collisions that transfer small amounts of energy, but the theory predicts a higher likelihood of energetic collisions than is observed experimentally. We explore possible explanations for this discrepancy in the dynamics of the collision excitation process.