Atom−polyatomic collisions: The role of pair correlation functions

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Abstract
Following a brief introduction to the relation between cross sections for atom−polyatomic collisions and the atom−pair correlation functions of the isolated polyatomic, we discuss properties of the correlation functions (such as sum rules and moments) relevant to experimental interpretation. Correlation functions are obtained analytically for polyatomics with harmonic vibrational motions, in their body−fixed reference frame. Rotational motions are then described within a short time expansion which provides a physical picture of rotational energy transfer for each vibrational transition. The obtained results are valid for multiquantum vibrational transitions. Gaussian rotational distributions are found for each vibrational transition, with parameters explicitly given by the theory. Relationships among collision times and rotational– vibrational periods, and the shapes of correlation functions vs. energy transfer are briefly discussed.