Pressure broadening and shifting in microwave and infrared spectra of molecules of arbitrary symmetry: An irreducible tensor approach

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Abstract
Contributions to the interruption function S(b) used in semiclassical perturbation approaches to impact broadening and shifting of microwave and infrared molecular gas spectra are derived by irreducible tensor methods for molecules of arbitrary symmetry. Results are given explicitly for long‐range intermolecular interactions: up to R−5 for the electrostatic interactions and to R−7 for the induction and dispersion interactions. A new contribution to S(b) is found that has no counterpart for the case of two interacting linear molecules; all other terms are appropriate generalizations of the linear molecules case. For the three cases of asymmetric tops, symmetric tops, and linear molecules, group‐theoretical arguments are given that simplify the computation of certain reduced matrix elements that occur in the theory. Results are given in detail for the case in which both radiating and perturbing molecules are linear, and errors in the published literature concerning the contributions to S(b) in this case are corrected.

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