Spectral band wings and rate constants of rotational relaxation as data source on molecular torques

Abstract

The factor Γ₄(Δω) describing the intensity distribution at large detunings Δω from a vibrational band centre is calculated for classical linear rotators in a buffer monoatomic gas. A formalism developed uses the theory of moments and is appropriate for a spectroscopy of any rank. The invariant form of the interaction potential and the irreducible tensor approach are exploited to derive the third- and fourth-order Poisson brackets of spectroscopic quantities. The anisotropy of the pair distribution function is analytically incorporated in the formulas for zeroth and second moments of the torque spectra appearing in the wing distributions. By a similar technique, the relaxation rates of rotational energy and momentum are studied. Useful analytical relations are found in the fast-collision limit. Calculations performed for CO+ He and CO₂+ He systems permit one to check the accuracy of the current models based on the infinite order sudden approximation and are in reasonable agreement with available experimental IR and NMR data.