On rotational relaxation of spherical gas molecules

Abstract

The Bryan-Pidduck model for collisions between particles with rotational degrees of freedom is modified in order to improve the description of rotational relaxation in mixtures of gases in which one of the components consists of structureless particles. The decisive parameter in the theory is the dimensionless quantity K α * = I α/ m α( r α *) 2 where I α is the moment of inertia of the particles of species α, m α their molecular mass, whereas r α * is the effective molecular radius of these particles. For the atomic species γ which cannot exchange their rotational energy, K γ * is infinite. Simple expressions for the rotational relaxation number Z rot are derived. The values for Z rot calculated for pure gases and for α-γ mixtures are in reasonable agreement with experimental results.