Role of N2(A′ 5Σ+g) in the enhancement of N2B 3Πg(V=10) populations in the afterglow

Time-resolved spectroscopic observations of the N2 1PG afterglow, B 3Πg→A 3Σ+u, following a pulsed discharge show both an enhancement in the overall intensity and significant changes the shape of bands which arise from the v=10 level of the B 3Πg. Model results indicate that these changes in shape are produced by an enhancement of the population of the low J levels of the Ω=2 component of the v=10 level. In addition, we also observe bands of the Herman Infrared system of N2 (HIR), C″ 5Πu→A′ 5Σ+g, specifically the (3,1) and (2,0) bands. During the afterglow, both the 1PG and HIR are being produced by energy pooling processes. The time-dependent increase of the 1PG v′=10 band intensities show a strong correlation with the variation in the HIR band intensities which predominately populate the lower levels of the A′ 5Σ+g. Recent work has shown the A′ 5Σ+g to have a significantly deeper potential well than previously thought so that it is now thought to cross the B 3Πg very close to v=10 rather than v=12. Consequently, we consider the A′ 5Σ+g to be the most likely candidate as the source of the observed intensity enhancements in the v=10 level of the B 3Πg. Based on our measurements and a simple model of the afterglow we have estimated the apparent rate coefficient for collisional transfer between A′ 5Σ+g and the high v levels of the B 3Πg due to collisions with the N2 ground state. The value for collisional transfer from A′ to B is approximately 1.0×10−11 cc/molecule s. Our observations indicate the A′ 5Σ+g may have an even deeper potential and we estimate an upper bound for v=0 to be ∼3590±32 cm−1 below the dissociation limit which is ∼500±32 cm−1 deeper than the recent theoretical estimate.