Monte Carlo calculation of the translational relaxation of superthermal H atoms in thermal H2 gas

We propose a simple and reliable method to study the translational relaxation of 'hot' H atoms following their production by chemical mechanisms. The problem is relevant to PDR's, shocks, photospheres, atmospheric entry problems. We show that the thermalization of H atoms can be conveniently studied by a simple method and set the basis for further investigations. The method adopted is Monte Carlo method including the thermal distribution of background molecules. The transport cross section is determined by the inversion of transport data. Plots of the collisions density of H atoms in H$_{2}$ gas are calculated and discussed also in the context of simple theories. The application of the results to astrophysical problems is outlined including numerical results for the reaction H + H$_{2}$O $\rightarrow$ H$_{2}$ + OH.
Comment: Accepted to Astrophysical Journal