Vibrational and rotational excitation within the X 1Σ state of N2 during the pulsed electric discharge and in the afterglow

The time transients of vibrational/rotational excitation up to v = 6 level of the ground electronic state of nitrogen were measured in a positive column during the 1 mu s pulsed electric discharges, and in the afterglow. The peak current densities were up to 25 A cm(-2) at the gas pressure of 5 Torr. During the active discharge the energy was transferred mainly into vibrational levels, primarily above v = 1, resulting in highly non Boltzmann distribution. The vibrational distribution became Boltzmann-like approximately 80 mu s after the discharge pulse and remained of this character until the next pulse. Rapid rotational heating was observed immediately following the cessation of the discharge current. The rotational temperature had risen from about 300 K during the discharge to more than 3000 K within the first 80 mu s of the afterglow and returned later to ambient ( 300 K) in less than 100 mu s. Its peak coincided with the time when the redistributed vibrational populations closely resembled the Boltzmann distribution. The vibrational populations could be described by a single temperature ( approximately 3000 K) from 100 mu s till nearly 1 ms after the discharge. All vibrational bands could be well described by the same rotational temperature at all times. Standard, coherent anti-Stokes Raman spectroscopy was used in all measurements.