Modelling the input and relaxation of vibrational energy in CO2 plasmas

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 similar to 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 900K, 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.