N2(C3Πu)→N2(B3Πg)+hν fluorescence increase due to collisional intermolecular energy transfer induced by discharged O2 in active nitrogen and oxygen mixtures

This work is a further investigation of increases in violet and UV fluorescence in various flowing nitrogen afterglows, when oxygen discharged in a microwave (μ−w) cavity is added to active nitrogen and oxygen mixtures downstream of the μ−w discharge zones of nitrogen and oxygen. The present N2 second positive band system (pbs) fluorescence (i.e. N2(C3Πu, υ′→B3Πg,υ″)+hν) increases also occur, when an orange flame (previously reported) is visually observed in nitrogen afterglows of active nitrogen and oxygen, by adding μ−w discharged O2. The orange flame is reported to result from a collisional energy transfer between excited molecular oxygen and molecular nitrogen species. (Nitrogen was activated by two ways: (i) with or without argon in a μ−w discharge cavity and (ii) by reacting gaseous nitrogen with metastable argon, Ar(3P0,2), generated in μ−w discharged Ar.) The present, as well as previous, results indicate that the well-known metastable energy donor, N2(A3Σu+), is also an efficient energy acceptor from non-nitrogen species, namely from excited O2, most probably O2(α1Δg). In addition, by analyzing experimental results using two different conventional chemical kinetics approximations, a lower limit estimate (∼1×10−10 molecule−1 cm3 s−1) is deduced of the pseudo-unimolecular chemical reaction rate constant, kαA, for the energy transfer between O2(α1Δg), as the energy donor, and N2(A3Σu+), as the energy acceptor. Further, enhanced intensities of background N2+ first negative band system (nbs) emissions (i.e. N2(B2Σu+→X2Σg+)+hν) are observed along with enhanced background N2 second pbs emissions intensities caused by discharged oxygen, near a nitrogen pink afterglow. The energy transfer, responsible for the enhanced N2 first and second pbs emissions intensities and N2+ first nbs emissions intensities, may contribute to the corresponding upper atmospheric and space emissions, in particular to the various visible and UV short-lived (lasting a few to ∼ a thousand ms) emissions discovered since 1989, termed upper atmospheric “transient luminous events”.