Electron thermalization in gases. II. Neon, argon, krypton, and xenon

Abstract

Following the theoretical procedure outlined in an earlier paper [J. Chem. Phys. 72, 1657 (1980)], hereinafter referred as I, the present work in an extension to the other rare gases. The following quantities are computed and evaluated: thermalization time and the position distribution at thermalization, time-dependent relaxation rates and evolutions of the directed velocity, width of the positional distribution, and the diffusion coefficient. A Newtonian cooling law has been demonstrated when the effective electron temperature 〈T〉 is close to the gas temperature with an equation for the relaxation time of the excess electron temperature. Weighted moments of the form Mn=〈vnσm(v)〉T have been calculated for n=1 to 10, where σm is the momentum transfer cross section and the symbol 〈−−−〉T denotes averaging with respect to the equilibrium electron velocity distribution at T. The fifth and the seventh moments are related, respectively, to the energy loss rate when 〈T〉 is ≫T and to the Newtonian cooling rate then 〈T〉?T. As in I the thermalization parameters are largely independent of initial velocity if the initial electron kinetic energy is much greater than that for the Ramsauer minimum (Ar, Kr, and Xe). Otherwise the thermalization time is considerably reduced. A somewhat analogous situation in neon is attributed to the ’’incipient’’ Ramsauer effect. Thermalization time at gas temperature ∼300 K increases, according to the present work, in the sequence He, Xe, Kr, Ne, Ar which is contributed jointly by the mass ratio and the behavior of momentum transfer cross section at low energies including the presence or absence of the Ramsauer effect. Comparison with experiments have been made where possible.