IR photochemistry: A unified approach for single-channel reactions. I. Theory and computational examples

Abstract

A model for infrared multiphoton decomposition of polyatomic molecules based on an energy-grained master equation (EGME) shows remarkably uniform behavior over a wide range of physically reasonable model parameters. These parameters encompass the size of the molecule, the reaction threshold energy, the variation of the decomposition rate constant above the threshold, and the functional dependence of the infrared absorption process on the internal energy of the molecule. The results are shown to be uniformly well represented by a cumulative log–normal distribution function for reaction yield versus time or fluence. A complementary approach based on the distribution of first passage times for a Markovian stochastic process in discrete state space and continuous time shows that the yield behavior of the EGME can be conveniently calculated without solution of the full set of equations. The uniform behavior of the model results yields a powerful method for presenting and analyzing experimental data.