A RESOLUTION OF THE N-2 CARROLL-YOSHINO (C4'-X) BAND PROBLEM IN THE EARTHS ATMOSPHERE

In the study of UV airglow from the Earth's atmosphere the N-2 Carroll -Yoshino (CY) c(4)'(1) Sigma(u)(+) - X(1) Sigma(g)(+)(0,0) and (0,1) R ydberg band emissions near 958 Angstrom and 980 Angstrom, respectively , are found to be weak relative to the c(4)'(0) excitation rate. This result is surprising because laboratory measurements show that CY(0,0) and CY(0,1) are the brightest N-2 emission features between 910-1010 A even under optically thick conditions [Zipf and McLaughlin, 1978]. I n order to investigate the cause of this weak emission quantitatively, we have developed a resonant fluorescent scattering model for CY(0,0) and CY(0,1). The model is intended to be comprehensive, including mul tiple scattering, extinction, branching, escape to space, predissociat ion, and temperature effects Results show CY(0,0) photons are radiativ ely trapped and undergo resonant fluorescent scattering accompanied by substantial loss in the atmosphere. Indeed, the model predicts weak C Y(0,0) intensities, consistent with observations. We find that the mos t important loss processes for the CY(0,v'') system in the Earth's day glow are predissociation and branching to CY(0.1) followed by absorpti on by the overlapping, 100% predissociated Birge-Hopfield I(BH I)b(1)I I(u)(2) - X(1) Sigma(g)(+)(0) band. Near solar minimum, model CY(0,1) and (0,2) dayglow zenith intensities between 160-170 km range between 4-9 R and 0.5-1.5 R, respectively, where the lower number assumes 16.5 % predissociation of the c(4)'(0) state and the higher number assumes 1% predissociation. These intensities are all; consistent with observa tions reported by Morrison et al. [1990]. For the Earth's aurora, mode l CY(0,1) and (0,2) intensities averaged between 88 degrees-96 degrees from the zenith at 118.5 km range between 60-180 R and 150-390 R, res pectively and CY(0,2) intensities at 170 km range between 200-360 R. T hese results are consistent with upper limits from Feldman and Gentieu (1982) if the probability of c(4)'(0) predissociation is at least 9%. We also present qualitative arguments to explain the relatively brigh t CY(0,v'') emission on Titan and Triton.