Collisional Studies of Neutral Species at Very Low Temperature

In traditional collisional studies, the large number of thermally populated states and the nature of the molecular interaction cause much of the complexity. Thus, it is expected that the very large reduction in the number of thermally populated states at low temperature will make the relation between observables and the fundamental interactions significantly more direct.

A substantial body of experimental pressure broadening data has now been obtained by use of the collisional cooling technique ( 386, 411, 413, 418, 419, 420, 423, 441, 442, 449, 456) for CO, H₂S, HDO, CH₃F, and NO in collision with He and H₂. For a few of these intermolecular potentials obtained either by ab initio techniques or from the analyses of the spectra of weakly bound complexes are available and theoretical methods (e.g. MOLSCAT) make possible a direct comparison between experiment and theory.