MONTE-CARLO CALCULATION OF ROTATIONAL RELAXATION IN SMALL MOLECULES

The application of a direct simulation Monte Carlo procedure to the in vestigation of rotational relaxation in homogeneous gases is described in which the rotational-translational energy transfer is assumed to b e related to the fraction of inelastic collisions in terms of a rotati onal-translational coupling parameter. The energy dependence of the co upling parameter is investigated for the homonuclear diatomic molecule s H-2, N2, O2 and Cl2, and for the polyatomic species CO2, OCS, NH3, C H4, CH3Cl and C2H4. Rotational collision numbers are calculated for th ese molecules and the energy-dependent coupling parameter is used in t hermal conduction model calculations to investigate the breakdown of t ranslational and rotational equilibrium in supersonic expansions of CO 2, OCS and CH3Cl.