Ionization mechanism in a nitrogen glow discharge

Abstract

The electron distribution function has been calculated in nitrogen taking into account collisions of electrons with vibrationally excited molecules. Transport coefficients, vibrational excitation rates, excitation rates for the lowest-lying electronic states, and direct ionization rates are presented as a function of E/N (electric field to gas density ratio) for different values of the vibrational temperature. At low E/N values, a very large increase of the direct ionization rate is observed due to the rise of the tail of the electron distribution in presence of large vibrational populations. Ionization processes occuring in the collision of metastable molecules have also been investigated. It is concluded that in most glow discharge, ionization occurs mainly from associative ionization produced by collision between two metastable molecules in the a′∑−u state. Ionization due to collisions of electrons with metastable molecules was found to be unimportant because of the low concentration of metastable molecules in glow discharges.