Surprisal analysis and probability matrices for rotational energy transfer

The information-theoretic approach is applied to the analysis of state-to-state rotational energy transfer cross sections. The rotational surprisal is evaluated in the usual way, in terms of the deviance of the cross sections from their reference ("prior") values. The surprisal is found to be an essentially linear function of the energy transferred. This behavior accounts for the experimentally observed exponential gap law for the hydrogen halide systems. The data base here analyzed (taken from the literature) is largely computational in origin: quantal calculations for the hydrogenic systems H₂+H, He, Li⁺; HD+He; D₂+H and for the N ₂+Ar system; and classical trajectory results for H ₂+Li⁺; D₂+Li⁺ and N₂+Ar. The surprisal analysis not only serves to compact a large body of data but also aids in the interpretation of the results. A single surprisal parameter θ_R suffices to account for the (relative) magnitude of all state-to-state inelastic cross sections at a given energy.