Modelling the input and relaxation of vibrational energy in CO2 plasmas

Abstract

A consistent theoretical analysis of a pulsed DC glow discharge operating at pressure of 5 Torr, current of 50 mA and plasma pulse of 5 ms in CO2 is presented. The model couples the electron Boltzmann equation to a rate balance equations involving ~70 individual vibrational states. The kinetic scheme and the corresponding e–V, V–T and V–V rate coefficients are validated via comparison between the model predictions and recent experimental data available in literature. The bending and symmetric vibrational levels show a continuous increase along the plasma pulse while the levels in the asymmetric mode present a maximum at around 0.7 ms. A corresponding maximum of the temperature of the asymmetric stretch vibration mode is observed as well at the start of the pulse reaching a value of about 900 K, well above the vibrational temperatures of the symmetric and bending modes, which remain always nearly equilibrated. A quick thermalization of the CO2 vibrational temperatures is always observed in the afterglow.