Non-equilibrium vibrational level distribution of the N 2 gas molecules in microwave electric field

Abstract The population of vibrational levels of the N 2 gas molecules in the conditions of low-pressure and low-temperature plasma induced by an external microwave (MW) electric field was investigated. The calculations were performed by using an extended Monte-Carlo simulation of electron transport through the N 2 molecule gas. The simulation included processes of electron–molecule elastic scattering, electron impact vibrational excitation, electronic excitation, dissociation and ionisation of the N 2 molecules. The electron–molecule super elastic scattering and de-excitations of excited molecular vibrational levels were also included. The algorithm tracks the dynamic balance between electron impact vibrational excitation and de-excitation processes on the N 2 gas ensemble. The processes of vibrational population redistribution and relaxation, induced by the gas molecule–molecule collisions, are also included in the simulation. This is achieved through the kinetic module of algorithm by solving master balance equations at every simulation step. All these simulated processes jointly change the states both the molecular and the electronic ensembles, and self-consistently evolve to a dynamic equilibrium state. In this way, a new self-consistent method of simulation is developed. The investigation was conducted in the conditions of the low-pressure and low-temperature plasma at the N 2 gas temperature of 300 K, when the gas collision vibrational population redistribution is a concurrent process to the electron impact vibrational population. The calculations for temporal development and the dynamic equilibrium vibrational level populations were performed for the standard MW frequency value of 2.45 GHz, at effective reduced electric field ( E / N ) values from 40 Td to 70 Td. The study also includes vibrational level populations in the conditions of various ratios of electron concentration to gas density. In addition, an orthogonal magnetic field to MW electric field was included in the simulation in order to investigate the vibrational level population at the region of electron cyclotron resonance.