Kinetics of a, B, and C Triplet States of Molecular Nitrogen in the Pulsed Discharge and Afterglow.

Density transients of the three triplet states of molecular nitrogen: A^3Sigma_sp {u}{+}, B^3Pi_ g, and C^3Pi_ u were measured in a positive column of moderate-current nitrogen pulsed discharge and in its afterglow. The study encompassed: (1) Population inversion between A ^3Sigma_sp{u}{+}(v ^{''} = 0) and B^3Pi_ g(v^' = 2) states in the early stage of a discharge; (2) Comparison of vibrational temperatures of C ^3Pi_ u and X^1 Sigma_sp{g}{+} states in pulsed discharges; (3) Decay of the A ^3Sigma_sp{u}{+}(v ^{''} = 0)<=vel in the early afterglow. Time-dependent absolute density of N_2(A^3Sigma_sp {u}{+}, v^{'' } = 0) molecules was measured using the high resolution laser absorption spectroscopy within the first positive system of N_2. Emission within the second positive system was used to measure vibrational distribution of the C^3Pi_ u state. The experiments were performed at various pressures (0.25-6 Torr), currents densities (0.6-16 A/cm ^2), and pulse lengths (5-30 mus). The population inversion was found to be present during the first 3-6 mus of the discharge pulse. The B^3Pi_ g(v^ ' = 2) density exceeded A^3 Sigma_sp{u}{+}(v^ {''} = 0) by 0.3 times 10^{12} cm^{ -3} at the peak current of 1 A and pressure of 0.5 Torr. Vibrational temperatures of the C ^3Pi_ u state were found to be higher than the respective values for the X ^1Sigma_sp{g}{+} state by up to a factor of 3 at the beginning of the pulse. In the early afterglow, the lifetimes of N _2(A^3Sigma_sp{u}{+ }, v^{''} = 0) metastables were ranging from 100 to 470 mus. It was shown that the loss processes in this case are due to diffusion, quenching by nitrogen atoms, and self-destruction in energy-pooling reactions. The postulated models of the triplet states kinetics, based on reaction rates, include excitation by electrons, collisions with nitrogen molecules and atoms, radiative cascading and diffusion. Vibrational excitation of X ^1Sigma_sp{g}{+} is taken into account. Calculations simulate the measured time transients within experimental error.