A Monte Carlo study of energy transfer in thermal unimolecular reactions: an application to diatomic dissociation

Abstract

The Monte Carlo method has been used to develop a model that stimulates the low pressure, non-equilibrium unimolecular decomposition of a diatomic molecule. Through the inversion of a simple exponential transition probability function, expressions have been derived for generating random energy jumps. These energy jumps correspond to energy transitions induced through single collision events in an unspecified heat bath gas. A version of the model involving only vibrational energy jumps, reproduces the rate constants calculated from a corresponding analytical solution. For a more realistic model, involving rotational and vibrational energy jumps, the results indicate, that when vibrational energy transfer is inefficient, those molecules that dissociate are rotationally excited. Furthermore, the vibrational energy states of the non-reactive molecules are extensively depleted down to quite low energies, an effect that arises from dissociation through rotational excitation.