A partially ergodic multiple encounter theory of collisional energy transfer

A semiempirical extension of the ergodic collision theory of collisional energy transfer is proposed. The new theory is based on a model of a collision as composed of one or more hard encounters during which microcanonical energy redistribution occurs over a subset of reactant and medium degrees of freedom. Depending on the strength of an attractive potential and the energy in the relative translation the collision complex may after a hard encounter decompose or produce repeated hard encounters before eventually decomposing into products. The new multiple encounter theory requires some knowledge of the interaction strength and the number of degrees of freedom of target and projectile molecules that are active in an encounter. It then predicts the energy and temperature dependence of the average energy transferred per collision [Delta E] and the underlying energy transfer kernel P(E\E). The content of the theory is illustrated in model calculations and compared with experimental data for the target molecules azulene, toluene, cycloheptatriene and difluorodichloromethane.