抄録
The isotope effects of H2 and D2 on the thermalization of epithermal electrons in gases are studied with the Monte Carlo simulation using the experimental cross sections. The influence of the gas temperature T on the isotope effects is examined at T=300 K, 77 K [∼θr(H2)], and 40 K [∼θr(D2)], because the characteristic rotational temperature θr corresponds to the rotational threshold. The electron velocity distribution deviates significantly from the local Maxwell distribution (MD) in both H2 and D2; consequently the degradation of the effective electron temperature Te is slower than that obtained with the MD assumption. The electron thermalization time τth when Te⁄T=1.1 is larger than that for the MD to the extent of 290% in D2 at T=40 K. The isotope effect is most prominent for the pressure normalized thermalization time τthp at T=77 K [τthp(D2)⁄τthp(H2)=0.35] because θr(H2)\gtrsimT>θr(D2). Te and τthp are compared with those calculated from available experimental energy exchange rate coefficients.
