Monte Carlo calculation of rotational relaxation in small molecules

Abstract

The application of a direct simulation Monte Carlo procedure to the investigation of rotational relaxation in homogeneous gases is described in which the rotational–translational energy transfer is assumed to be related to the fraction of inelastic collisions in terms of a rotational–translational coupling parameter. The energy dependence of the coupling parameter is investigated for the homonuclear diatomic molecules H₂, N₂, O₂ and Cl₂, and for the polyatomic species CO₂, OCS, NH₃, CH₄, CH₃Cl and C₂H₄. Rotational collision numbers are calculated for these molecules and the energy-dependent coupling parameter is used in thermal conduction model calculations to investigate the breakdown of translational and rotational equilibrium in supersonic expansions of CO₂, OCS and CH₃Cl.