Information theoretic analysis of multiphoton excitation and collisional deactivation in polyatomic molecules

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Abstract
The procedure of maximal entropy is applied to characterize the three distributions over energy states which are of direct interest for studies of multiple photon excitation of polyatomic molecules. These distributions are (a) the original population of the different energy states given the mean number of photons absorbed, (b) the distribution over the final energy states after a single collision, given a well‐defined initial energy state and the mean energy transfer per collision, and (c) the time evolution of the population of the different energy states due to collisional deactivation, given the mean energy transfer per collision. Good agreement with experimentally determined values of 〈ΔE〉, the average amount of energy removed in a collision, are obtained for deactivation of sec‐butyl, cyclohexane, 3‐hexyl, and β‐naphthylamine by structureless collision partners such as He or H2. The vibrational relaxation surprisal parameter is found to be λ1?0.1 for all these systems. This is much closer to a statistical, or strong‐collision limit than vibrational deactivation of diatomics by atoms, for which λ1?1.0. Deactivation most likely proceeds through a sequence of maximal‐entropy distributions. These results are used to interpret experimental data on the infrared multiphoton reactions of deuterated vinyl chloride.

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