Kinetic model of vibrational relaxation in a humid-air pulsed corona discharge

The effect of humidity on the vibrational relaxation of O(2)(v) and N(2)(v) in a humid-air pulsed corona discharge is studied using a kinetic model. We previously showed that humidity markedly increases the vibration-to-translation (V-T) rate of molecules in a humid-air pulsed corona discharge by measuring O(2)(v) density (Ono et al 2010 Plasma Sources Sci. Technol. 19 015009). In this paper, we numerically calculate the vibrational kinetics of O(2), N(2) and H(2)O to study the reason behind the acceleration of V-T in the presence of humidity. The calculation closely reproduces the measured acceleration of V-T due to humidity, and shows that the increase in the V-T rate is caused by the fast vibration-to-vibration (V-V) processes of O(2)-H(2)O and N(2)-H(2)O and the subsequent rapid V-T process of H(2)O-H(2)O. In addition, it is shown that O atom density is also important in the vibrational kinetics owing to the rapid V-T process of O(2)-O.