Further observations on the nitrogen orange afterglow

Abstract

We have extended earlier observations on the nitrogen orange afterglow that results from the excitation of N2(B 3Πg,v′=1–12) in the energy transfer reaction between N2(A 3Σ+u) and N2(X,v≥4). Spectral observations out to 1550 nm show that N2(B,v′=0) accounts for about 38% of the total N2(B) excitation. This makes the rate coefficient for N2(B) excitation in the energy-transfer reaction between N2(A) and N2(X,v≥4) equal to (4±2)×10−11 cm3 molecule−1 s−1. Experiments involving 14N2(A) and isotopically labeled 15N2(X,v) show 15N2(B) is the principal product. This demonstrates that the mechanism involves electronic energy transfer from the N2(A) to the N2(X,v). The vibrational distributions of N2(B,v≥4) are qualitatively similar whether 15N2(v) or 14N2(v) is excited although the magnitude of 15N2(B,v≥4) excitation is about 20% larger. These distributions can be characterized roughly as a 5200 K Boltzmann distribution. In contrast, the vibronic levels of 14N2(B,v=0–2) are substantially more excited than are those of 15N2(B,v=0–2). Interestingly, the overall excitation rates for both 14N2(X,v) and 15N2(X,v) are the same to within 20%. Adding 14N2(X) to the mixture of N2(A) with 15N2(X,v) results in quenching of 15N2(B) and the concomitant excitation of 14N2(B). The rate coefficient for this electronic energy exchange reaction is (8±2)×10−11 cm3 molecule−1 s−1, about 2.5 times greater than the rate coefficient for N2(B) removal by N2.