Rydberg states population via three-body and dissociative recombination in low-temperature plasmas of rare gas mixtures

Abstract

We study various physical mechanisms of electron-ion recombination accompanied by the formation of Rydberg atoms in plasmas containing atomic and molecular ions. Analytical approach to the description of resonant mechanism of ternary electron capture associated with the non-adiabatic energy transfer from free electron to the electronic shell of a quasimolecular ion is developed. Similar technique is used for the evaluation of the integral contribution of all rovibrational states of a bound molecular ion to the Boltzmann-averaged cross section and rate constant of dissociative recombination (DR). Simple expressions for cross sections and rate constants of non-resonant electron capture to Rydberg states in ternary electron-ion-atom collisions are derived in the impulse approximation. We perform a comparative analysis of the efficiencies of resonant and non-resonant three-body recombination of electrons with atomic ions and DR of molecular ions in plasmas of rare gas mixtures, Rg/Xe, with small relative concentration of xenon ([Xe]=[Rg], Rg=He, Ne, Ar, Kr). It is shown that in a wide range of plasma parameters the resonant recombination mechanisms are predominant. The behavior and magnitudes of the recombination rate constants turn out to be quite different for heteronuclear ions with small (HeXe + and NeXe + , D 0 =13.1 and 33 meV) and moderate (ArXe + and KrXe + , D 0 = 171 and 400 meV) values of the dissociation energy.

Semiclassical theory of resonant dissociative excitation of molecular ions by electron impact

“…General formulae for the cross sections and rate constants of electron-impact resonant DE process are derived with explicit dependencies on the electron energy, and the gas, T, and electronic, T e , temperatures. Together with our previous results [39,59,60], the approach gives a unified treatment of the contributions from the DE and DR processes to the total rate of molecular ion breakup.…”

“…Due to strong influence of the spin-orbit coupling, no detailed studies of the coupling parameter were published to date. However, as was demonstrated in our recent work [39] on recombination, a simple semi-analytic approach based on vacancy model [66,67] can be sufficient to reproduce the general features of the cross sections and rate constants. The approach reduces the electronic shell of the ion to the effective one-electron vacancy ('hole') shell interacting with the incident electron.…”

“…Next we adopt a semiclassical approximation for the nonadiabatic transition matrix elements. A more elaborate semiquantal method can be derived using the results of our works [39,61]. Then (3) becomes…”

“…While these techniques allow for an accurate treatment of the process, their application to complex systems like rare gas mixture plasmas at room and elevated gas temperatures requires an enormous computational effort. To address this problem, several simplified approaches were proposed [36][37][38][39]. Most recent review of the respective theoretical methods can be found in [3].…”

Диссоциативная рекомбинация в послесвечении барьерного разряда в неоне низкого давления. Заселение атомов конфигурации 2p-=SUP=-5-=/SUP=-3d

“…С одной стороны, этот механизм деионизации определяет свойства широкого круга лабораторных плазменных объектов и является необходимым звеном в моделях звездной и планетной атмосфер [2]. С другой стороны, несмотря на долгую историю изучения процесса, обнаруживаются ранее неизвестные проявления DR даже в случае простейших молекулярных ионов, таких как H + 2 [3] или HeNe + [4], что стимулирует развитие новых подходов к расчету его основных характеристик-сечений и констант скорости [5]. Наиболее подробно обсуждаемый процесс изучен в плазме инертных газов, а наибольшее количество работ посвящено рекомбинации ионов Ne + 2 .…”