Low Energy Electron Impact Emission Cross Sections of the N2 LBH Band System With Importance to UV Planetary Remote Sensing

Abstract Far-ultraviolet (FUV, ∼135–165 nm) dayglow emissions from N 2 -rich Solar System Objects (SSOs) are dominated by the Lyman–Birge–Hopfield (LBH) band system. Consequently, observations from the Cassini Ultraviolet Imaging Spectrograph (UVIS) at Titan and the Global-scale Observations of the Limb and Disk (GOLD) mission at Earth use the LBH emission for upper atmospheric remote sensing at both SSOs. However, FUV dayglow-based remote sensing analysis has been hampered by large uncertainties in existing LBH emission cross sections, particularly at low photoelectron energies. We present laboratory measurements of emission cross sections obtained at low electron energies (16, 20, and 30 eV). Our laboratory apparatus employs a high-resolution, state-of-the-art monoenergetic electron beam source and a large (1.5-m diameter) chamber. With this apparatus, we produce single-particle excitation of the optically forbidden upper state of N 2 ( a 1 Π g -state), including cascade and collision induced excitation from nearby electronic states. The low energy electron impact cross sections from this study (at 16, 20, and 30 eV) are combined with our previous results to fit an analytic LBH cross section as a function of energy (16–200 eV).