Diffusion coefficients of two metastable states of the nitrogen molecule

Previous experiments of Ernest et al. (1986) showed the existence of a metastable state of the nitrogen molecule with a coefficient for diffusion through ground-state nitrogen of about one quarter of that of the well-known A(3) Sigma(u)(+) state. Both states were populated by pre-breakdown discharges through pure nitrogen. This paper presents further results on the diffusion of metastable excited molecules through nitrogen. The effects of varying background gas number density N and the reduced electric field E/N were explored, and data were taken in two ionization chambers with two different cathode materials. Consistent results are obtained with the different chambers and cathodes. The characteristic times for the decay of metastable population density are independent of E/N but scale with 1/N, consistent with the existence of two slowly diffusing metastable states of nitrogen. The values at 295 +/- 4 K of the product DmN, where D-m is the metastable diffusion coefficient, are 551 +/- 25 am(-1) s(-1) ((5.51 +/- 0.25) x 10(16) cm(-1) s(-1)) for the first slowly diffusing state and 158 +/- 17 am(-1) s(-1) for the second. Both states show very small quenching in collisions with ground-state nitrogen molecules. The first state is identified as the A(3) Sigma(u)(+) state. Far from having a small effect, the action of molecules in the second slowly diffusing state can dominate the ionization growth near breakdown.