A multispeed discrete‐velocity molecular model of a rarefied gas is developed which permits quantitatively accurate simulation of mixtures of molecules of different mass which have both translational and internal rotational energies. In particular, the molecules are represented as having three discrete velocity components and a single discrete internal energy that does not directly affect the translational motion. During binary collisions, rotational and translational kinetic energies are exchanged according to a phenomenological model. Results are presented for the thermal relaxation to equilibrium of mixtures of H_{2} and Ne, N_{2} and O_{2}, and N_{2} and CO_{2}. Good agreement is found with the corresponding continuous‐velocity results.

## REFERENCES

*Radiative Transfer*(Dover, New York, 1980).

*Transport Theory*(Wiley, New York, 1979).

*Rarefied Gas Dynamics: Proceedings of the First International Symposium*, Nice (Pergamon, New York, 1960).

*Lecture Notes in Physics*(Springer-Verlag, Berlin, 1975), Vol. 36.

*Rarefied Gas Dynamics*, Proceedings of 17th International Symposium on Rarefied Gas Dynamics, Aachen, edited by A. E. Beylich (VCH Verlagsgesellschaft, Weinheim, 1990).

*Rarefied Gas Dynamics: Theoretical and Computational Techniques*, Proceedings of 16th International Symposium on Rarefied Gas Dynamics, Pasadena, CA, edited by E. P. Muntz, D. P. Weaver, and D. H. Campbell (AIAA, Washington, DC, 1989);

*Lattice Gas Methods for Partial Differential Equations*(Addison-Wesley, Reading, MA, 1990).

*Progress in Aeronautics and Astronautics*, Twelfth International Symposium on Rarefied Gasdynamics, 7–11 July 1980 (AIAA, New York, 1981), pp. 239–255.

*Rarefied Gas Dynamics*, Proceedings of 5th Symposium on Rarefied Gas Dynamics, Oxford, England, edited by C, L. Brundin (Academic, New York, 1967), pp. 695–710.

*Molecular Gas Dynamics*(Clarendon, Oxford, 1976).

*Rarefied Gas Dynamics*, Proceedings of the 11th International Symposium on Rarefied Gas Dynamics, edited by R. Campargue, (CEA, Paris, 1979), Vol. 1.