Reactivity, relaxation and dissociation of vibrationally excited molecules in low-temperature plasma modeling

Abstract: Accurate modeling of low-temperature plasmas requires molecular collision input data, including the detail over the whole ladder of vibrational states. Obtaining this kind of detailed data is a big challenge, both theoretically and experimentally. These data can be calculated with the aid of simple models (for inelastic processes essentially based on forced harmonic oscillator mechanism), or with molecular dynamics at various levels, namely quasiclassical (QCT), semiclassical (SC), approximate and exact quantum mechanical methods, with computational cost rapidly increasing with accuracy. However, while accurate methods can become unfeasible when applied to the wide total energy ranges typically required in plasma modeling, more approximate semiclassical methods rapidly become efficient and accurate for increasing total energy, as shown in the literature. The best strategy is to study the limits of application of less accurate methods, to use them as a seamless continuation of accurate calculations on the total energy axis. In this sense, it is the current development about inelastic processes treated by QCT and SC methods. The aspect of special interest is the indication of a criterion for easily extracting the reliable QCT contribution to the inelastic process, treating the missing contributions by other SC methods in a restricted range. This procedure allows to optimize the use of different methods to maintain both a high level of accuracy and a high computational efficiency. As a consequence of the study about inelastic processes, a better comprehension and possible treatment of the dissociation mechanisms are obtained, with an indication of reliability of QCT results about this kind of process.