Intermolecular energy transfer effects in thermal unimolecular reactions

Abstract

Traditional unimolecular reaction rate theories have incorporated the strong collision assumption primarily to obtain a simple expression for k/sub uni/. However, it is known that many experimental studies do not provide the environment for strong collisions. Hence, weak collider corrections to the expression for k/sub uni/ have been empirically incorporated. We have derived a new self-contained expression for the many-level system which accounts for weak collision phenomena from first principles; the requirement for strong collision behavior is quantitatively described by this formulation. In this formalism the calculated rate constants are directly related to the average transition probabilities for energy transfer. Using this result it can be shown that ..beta..' and not ..beta.. is the correct collisional energy transfer efficiency to relate experimental data to model calculations. The prediction of energy transfer effects in model steady state thermal systems using temperature, falloff, dilution, transition, probabilities, and reactant complexity as variable parameters is discussed. Methods (information theory and model calculations) for obtaining energy transfer information from experimental data are presented. Non-steady-state solutions for weak colliders are evaluated for the cyclopropane system. 9 figures, 1 table.