Nitrogen vibrational temperature in repetitively pulsed air discharges

The vibrational degree of nitrogen is highly excited in low temperature plasma generated by air discharges. Based on harmonic oscillator model and the assumption of Boltzmann distribution of vibrational levels, the behavior of vibrational temperature during repetitively pulsed air discharges is investigated. The results show that the determinant factor of vibrational temperature is the competition between electron-vibrational (e-V) excitation process and vibrational-translational (V-T) relaxation process, while the chemical-vibrational (Chem-V) process involving oxygen atom also influences in highly excited vibrational state. For the e-V process, the characteristic relaxation time deduced from an empirical reciprocal law of transition rates agrees well with that from kinetic modeling. For the V-T process, the dominant role is played by oxygen atoms in dry air and water moleculars in humid air. If the density of oxygen atom is 1014 cm-3 and the vibrational temperature is 5000 K, the relaxation time during initial Chem-V process is in the order of 0.1~1 s.