Measurements of N<sub>2</sub> Vibrational Distribution Function in Pulsed Nanosecond Nonequilibrium Discharge by Spontaneous Raman Scattering

Spontaneous Raman spectroscopy has been used, in conjunction with a master equation kinetic model, to study vibrational energy loading and relaxation in nitrogen (P=100 torr), in a pin-topin, nanosecond pulsed electric discharge. A highly non-equilibrium vibrational distribution (up to v=12 significantly populated) was observed for time delays after the pulse ranging from 135 nsec to 10 msec. Approximately 35% of the total discharge energy was found to couple directly to the N2 vibrational mode via direct electron impact, a result found to be in good agreement with discharge model predictions. Following the discharge pulse, the total vibrational quanta in all observed levels (v=0-12) was seen to rise by a factor of approximately 70 percent, indicating further energy coupling into N2 vibrations post-discharge, consistent with previous Coherent Anti-Stokes Raman Spectroscopy (CARS) studies performed with the same discharge geometry. As a first attempt to account for this, a simple phenomenological E-V coupling model was incorporated into the master equation model. Significantly better overall agreement with the data, including the temporal evolution of the vibrational distribution function and total vibrational quanta was observed when a 30% energy defect into the N2(X,v) vibrational mode, during E-V transfer from quenching and pooling processes (involving the N2(A) and N2(C) excited electronic states), was assumed.