Modeling of molecular ions formation in cold rare-gas plasmas

Abstract

Molecular ions, in particular, dimeric rare-gas ions have a very important influence on the behavior of rare gas plasmas used in multiple fields. Therefore, the analysis and understanding of their formation are of great importance for the macroscopic modeling of these plasmas. The main objective of this work is to perform calculations of the rate constants of dimer ions formation in cold plasmas using rare gases as carriers over a wide range of reduced electric fields. To do so we have used mesoscopic data (cross sections) obtained from microscopic data (interaction potentials) for argon to provide reaction rate constants of the formation of Ar$_{2}^{+}$. Further, to perform our calculations we have considered all six lowest-lying electronic states of the Ar$_{2}^{+}$ ions. These six electronic states are classified in two fine structure states of the atomic ion, the ground state $^2P_{3/2}$ and the excited state $^2P_{1/2}$. A quasi-classical trajectory approach based on the nonadiabatic mean-field dynamics approach and \emph{Diatomics In Molecules} (DIM) model of the interactions in collisions complexes used in preceding studies to calculate the collision cross sections that we will use in the present work. These collision cross sections will feed a Monte Carlo code adapted and optimized for the calculation of auxiliary data such as collision energy distributions which are important to provide averaged, thermal ternary recombination rate constants of ground and excited states of the dimer ion. The ternary recombination rate constants calculated in this way are compared with the experimental measurements and theoretical data available in the literature. The results we have obtained, are close to these experimental and theoretical values for selected values of reduced electric fields, $E/N$= 1, 50, and 100 Td, with standard conditions of temperature $T$= 300 K and pressure $P=10^{5}$ Pa. Thus, these results are expected to be helpful in tuning cold plasma generators for specific applications.