The EUV airglow of Titan : Production and loss of N 2 c * 4 ( 0 ) 2 X

The N2 Carroll-Yoshino (CY) c94 2 X (0,0) and (0,1) Rydberg bands between 95 and 99 nm were reported to be the most prominent EUV emission features in Voyager 1 ultraviolet spectrometer (UVS) airglow spectra from Titan’s atmosphere. Although c94 is strongly excited by photoelectron impact, the (0,0) band is optically thick near peak production, so a multiple-scattering model is employed to calculate (0,v0) nadir-viewing intensities. The model accounts for all known loss processes and quantifies the redistribution of photons to (0,v0 . 0). Results show 7.6 R of (0,1) intensity, in agreement with reported observations (5–10 R), and 0.2 R of (0,0), in spectacular disagreement with reported observations (6–10 R). Nadir-viewing intensities of all other expected NI multiplets and N2 bands in the brightest portion of the EUV airglow spectrum (92.0–101.5 nm) are also calculated using photodissociative ionization of N2 and photoelectron impact on N2. It is found that NI multiplets and N2 bands near (0,0) and unresolved by the UVS combine to produce 8.3 R, consistent with that reported for (0,0) and indicating that it was misidentified in previous analyses. The Ultraviolet Imaging Spectrograph (UVIS) on Cassini should unambiguously distinguish any (0,0) intensity from the brightest features nearby.