Monte Carlo simulation of electron thermalization in gases. II. Subexcitation electrons in molecular hydrogen

Abstract

The Monte Carlo simulation (MCS) of the thermalization of low-energy electrons (ε≲0.1 eV) due to the rotationally inelastic and elastic collisions in normal H2 [J. Chem. Phys. 79, 3367 (1983), referred to as I] is extended to high-energy subexcitation electrons (ε∼1 eV) by taking into account the vibrationally inelastic collisions and using available experimental cross section data. The MCS is performed for the thermalization of subexcitation electrons with the initial Maxwell, δ function, or Platzman velocity distribution at the initial effective electron temperature 103≤Te(0)≤3×104 K in normal H2 at the gas temperature 77≤T≤103 K. The electron velocity distribution deviates significantly from the local Maxwell distribution (MD) even for the initial Maxwell distribution owing to the vibrationally and rotationally inelastic collisions. Consequently, the degradation of the effective electron temperature Te (reduced mean electron energy) is slower than that obtained with the MD assumption. The thermalization time τth when Te/T=1.1 is insensitive to the initial electron velocity distribution and effective electron temperature. At T≳300 K, τth is about 70% larger than that for the MD, where τth is dominated by the rotationally inelastic collisions. At the low gas temperature T=77 K, τth is about 160% larger than that for the MD, where τth is dominated by the elastic collisions. The MCS value of τth p=3.4 μs Torr at T=300 K, where p is the gas pressure, is about 130% larger than the experimental value of 1.5 μs Torr obtained by Warman and Sauer using the assumption of the constant energy exchange rate coefficient and about 40% larger than the theoretical value of 2.37 μs Torr obtained by Tembe and Mozumder using the approximate theory based on the MD assumption.