Impact Theory of the Noble-Gas-Broadened HCl Vibration-Rotation Lines

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Abstract
The widths and shifts of the noble-gas-broadened HCl (0-1) and (0-2) band vibration-rotation lines are calculated using an impact theory similar to Anderson's. To obtain agreement with the experimentally observed shifts, Anderson's approach is modified in that the imaginary parts of the optical cross sections are calculated in greater detail. The cross sections are evaluated in a representation which allows further understanding of the physical processes active in impact broadening. It is shown that many broadening and shifting characteristics can be explained upon taking into account the eccentricity of the HCl molecule, in which the centers of charge and mass do not coincide. Substantial agreement with experiment is reached, although several features of the observed shapes and shifts—particularly the variation in width with perturber species—remain unexplained.