Rotational relaxation of OCS by spherical and nearly spherical perturbers

Collision cross sections for the transverse relaxation of OCS by spherical and nearly spherical perturbers have been measured. The observed cross sections vary linearly with β=[I²₂/(I₁+I₂)²α²₂M]^1/5, where I₁ and I₂ are the ionization energies of OCS and the perturber. α₂ is the polarizability of the perturber, and M is the reduced mass of the colliding molecules. Calculations based on the Anderson-Tsao-Curnutte theory using a simple dispersion force model for the OCS-perturber interaction are in qualitative agreement with the experimental results. By doubling the strength of the dispersion forces used to model the OCS-perturber interactions, the calculated cross sections are brought into agreement with the measured ones. The observed linear relation between the cross section and β can be used to predict cross sections for other (polar molecule)-(nonpolar nearly spherical perturber) collisions.