This work is a further investigation of increases in violet and UV fluorescence in various flowing nitrogen afterglows, when oxygen discharged in a microwave (mu-w) cavity is added to active nitrogen and oxygen mixtures downstream of the mu-w discharge zones of nitrogen and oxygen. The present N-2 second positive band system (pbs) fluorescence (i.e. N-2(C-3 Pi(u),upsilon'-> B-3 Pi(g),upsilon")+hv) increases also occur, when an orange flame (previously reported) is visually observed in nitrogen afterglows of active nitrogen and oxygen, by adding mu-w discharged O-2. 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 mu-w discharge cavity and (ii) by reacting gaseous nitrogen with metastable argon, Ar(P-3(0,2)), generated in mu-w discharged At.) The present, as well as previous, results indicate that the well-known metastable energy donor, N-2(A(3)Sigma(+)(u)), is also an efficient energy acceptor from non-nitrogen species, namely from excited O-2, most probably O-2(alpha(1)Delta(g)). In addition, by analyzing experimental results using two different conventional chemical kinetics approximations, a lower limit estimate (similar to 1 x 10(-10) molecule(-1) cm(3) s(-1)) is deduced of the pseudo-unimolecular chemical reaction rate constant, k(alpha A), for the energy transfer between O-2(alpha(1)Delta(g)), as the energy donor, and N-2(A(3)Sigma(+)(u)), as the energy acceptor. Further, enhanced intensities of background N-2(+) first negative band system (nbs) emissions (i.e. N-2(B-2 Sigma(+)(u) -> X-2 Sigma(+)(g)) + hv) are observed along with enhanced background N-2 second pbs emissions intensities caused by discharged oxygen, near a nitrogen pink afterglow. The energy transfer, responsible for the enhanced N-2 first and second pbs emissions intensities and N-2(+) first ribs 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 similar to a thousand ms) emissions discovered since 1989, termed upper atmospheric "transient luminous events".
Oxford
Εθνικό Ίδρυμα Ερευνών (ΕΙΕ)
