Atomic and molecular emissions in the middle ultraviolet dayglow

Dayglow spectra in the middle ultraviolet, obtained during a sounding rocke t flight from White Sands Missile Range in 1992, have been analyzed to dete rmine the altitude distributions of thermospheric atomic and molecular spec ies and to address a number of problems related to airglow excitation mecha nisms. Among the atomic and molecular profiles retrieved are the N-2 second positive, N-2 Vegard-Kaplan and NO gamma band systems, and the OI 297.2 nm , OII 247.0 nm, and NII 214.3 nm emissions. A self-consistent study of the emission profiles was conducted by comparing observed intensities with one another and to forward models. Model photoelectron and photon fluxes were g enerated by the field line interhemispheric plasma model (FLIP) and two sol ar flux models. Neutral densities were obtained from mass-spectrometer/inco herent scatter (MSIS)-90. The results from the data analysis suggest that t he major species' densities are within 40% of MSIS values. Evidence for the accuracy of the modeled densities and fluxes is seen in the close agreemen t between the calculated and observed intensities of the N-2 second positiv e emission. Analysis of the OI 297.2 nm emission shows that the reaction N- 2(A) + O is the dominant source of O(S-1) in the daytime thermosphere. The data imply that the vibrationally averaged yield of O(S-1) from the reactio n is 0.43 +/- 0.12, which is smaller than the laboratory value measured for the N,(A, nu' = 0) level. The cause of a disagreement between model and da ta for the Vegard-Kaplan emission is unclear, but the discrepancy can be el iminated if the N,(A) + O quenching coefficient or the A state lifetime is increased by a factor between 2 and 4. The observed intensity of OII 247.0 nm is greater than expected by a factor of 2, implying possible inadequacie s in the EUVAC and/or EUV91 solar models used in the analysis.