THE INFLUENCE OF EXCITED-STATES ON THE KINETICS OF EXCITATION AND DISSOCIATION IN GAS-MIXTURES CONTAINING METHANE

In this paper, we extend the calculations for rare gas discharges, whi ch aim to establish the influence of excited states on the kinetics of electron-induced excitation, to rare gas-methane mixtures and pure me thane which are often used in diamond-like film deposition. In particu lar, we address the effect of non-thermal vibrational populations on t he rate coefficients in methane-containing gas discharges using the pr ocedure applied previously for pure silane. Furthermore, we investigat e the kinetics of electronically excited levels of rare gases and meth ane in the presence of a significant population of excited states. The se states may contribute to the overall ionization, excitation and dis sociation rates through stepwise processes, superelastic collisions an d energy transfer processes. The influence of superelastic processes o n the development of the negative differential conductivity (NDC) is d iscussed on the basis of the momentum transfer theory, and it is shown that the NDC is reduced when significant populations of excited state s are present. This is of importance for calculations of the transport coefficients for a.c. electric fields where NDC leads to a complex te mporal dependence of the drift velocity and thus directly affects the power deposition in the discharge. Finally, we present the rate and tr ansport coefficients calculated for methane in r.f, fields based on th e Monte Carlo simulation for time-dependent fields. A good agreement w ith the effective field approximation and earlier Boltzmann calculatio ns is found.