dayglow emission observed by the Far Ultraviolet Spectroscopic Explorer

[1] Terrestrial thermospheric dayglow emission from the coupled and overlapping c0 4 Su (0) and b0 Su (1) levels of molecular nitrogen, observed by the Far Ultraviolet Spectroscopic Explorer, is analyzed with the aid of a coupled channels quantum mechanical model of N2 spectroscopy and predissociation dynamics. Model emission spectra for the mixed c0 4 Su (0) b0 Su(1) X Sg(vi = 2, 6–9) transitions, calculated for the case of excitation by photoelectron impact, are in excellent agreement with the observations. While the principal excitation mechanism for N2 in the thermosphere is photoelectron impact, evidence is also found in other transitions of resonant fluorescence, induced by lines in the solar atomic hydrogen Lyman series, atomic oxygen transitions, and other N2 bands. The observed emission rate of the c 0 4 Su (0) b0 Su(1) X Sg(0) band is 1% of that inferred from the emission rates to X Sg(vi > 2) levels. A qualitative explanation is given for the drastically reduced intensity and band shape distortion observed in the c0 4 Su (0) X Sg(0) emission band. Estimates of the total electron excitation rates for the nominal b0 Su (1) and c0 4 Su (0) levels are determined from the spectrum by extrapolating the model through regions containing unmeasured and/or resonantly absorbed bands.