Molecular nitrogen Carroll‐Yoshino v′ = 0 emission in the thermospheric dayglow as seen by the Far Ultraviolet Spectroscopic Explorer

Molecular nitrogen (N 2 ) Carroll‐Yoshino excitation is of considerable interest in the analysis of EUV‐FUV observations obtained from several solar system objects (Earth, Titan, and Triton). The fundamental c 4 ′(0, 0) band at 958 Å is a strong transition excited by photoelectron impact and hence is bright under optically thin conditions. On Earth c 4 ′(0, 0) is optically thick near the altitude of peak photoelectron excitation and the emergent (0, 0) emission is weak. Past analyses of EUV airglow spectra focused on the roles of (0, v ″ ≤ 2) photon redistribution and predissociation enhancement resulting from multiple scattering in accounting for reduced emission. The role of (0, v ″ > 2) fluorescence was deemed minor. Now, high‐resolution dayglow measurements by the Far Ultraviolet Spectroscopic Explorer (FUSE) made in September 1999 reveal c 4 ′(0, v ″ = 6–9) fluorescence bands much brighter than expected. The results of an analysis of FUSE dayside disk measurements are presented, and the observed (0, v ″) emission is discussed in the context of results from a multiple scattering model. The c 4 ′(0, 9) band in particular stands out as a potentially useful remote sensing observable.