The ultraviolet dayglow 1. Far UV emissions of N and N2

Abstract

Far ultraviolet rocket spectra of N I and N2 dayglow emissions have been analyzed by using AE‐E photoelectron spectra, laboratory‐measured excitation cross sections, and photochemical models of atomic nitrogen. A self‐consistent picture of both optically thick and thin emission features is found by using a model in which the principal production mechanism for N I 1200‐Å and 1493‐Å photons is photodissociative excitation of N2. The aeronomic data require that ∼50–70% of the excited 4P atoms produced dissociatively have velocities within the Doppler core of the ambient nitrogen atoms, contrary to the expectation that those atoms are produced with large excess kinetic energy. The derived atomic nitrogen density has a maximum density of 2.7 × 107 cm−3 at 170 km, a value that is within 40% of that from recent models of odd nitrogen photochemistry.