DIRECT SIMULATION OF ROTATIONAL RELAXATION USING STATE-TO-STATE CROSS-SECTIONS

Rotational relaxation in para-hydrogen (p-H-2) is modeled using a direct simulation Monte Carlo (DSMC) method with state-to-state collision cross sections and the results are compared with a simple Borgnakke-Larsen (B-L) type rotational relaxation model. The detailed simulation shows that the rotational population relaxes through nonBoltzmann distributions as expected. However, even the rotational energy relaxation shows some unexpected features that cannot be described by the simple model. For initial states with strong nonequilibrium, the simple B-L model fails to provide even a qualitative description of the relaxation of the rotational energy of p-H-2.