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.

THE HIGH-RESOLUTION EXTREME-ULTRAVIOLET SPECTRUM OF N 2 BY ELECTRON IMPACT

“…The strong atomic (ion) features attributed to PDI lie near 885,905,916,954,964,1085,1134,1200, and 1243 Å. Other excitation processes are also possible in an N 2 atmosphere in varying amounts (Meier et al 1980;Bishop & Feldman 2003).…”

The extreme ultraviolet day airglow

“…Some information, however, can be obtained by comparing the observed intensity ratios with previous dayglow observations , theoretical calculations [Cohen and Dalgarno, 1964;Luken and Sinanoglu, 1976;Wiese et al, 1966], and laboratory measurements [Morrison et al, 1981[Morrison et al, , 1983. The results of this analysis are summarized in Table 2 The N2 Lyman-Birge-Hopfield (LBH) system (of which only the (6,0) 1325-• band is observed with the EUV spectrometer) is produced by photoelectron impact [Meier et al, 1980]. This is probably true for the Birge-Hopfield (BH) bands as well, but the resultant intensities are highly affected by radiation entrapment and predissociation.…”

Observations of the far ultraviolet nightglow

“…Although the N2 concentration is very high at 100 km altitude, the LBH system is electric dipole forbidden, and an optically thin medium seems to be more appropriate for this case. As pointed out by Meier et al [1980], magnetic dipole and partial electric quadrupole transitions are allowed, so that high low altitude N2 densities might permit some leakage of daytime photons into the nighttime. The self-absorption effects noted by Meier et al are greatly reduced, however, when the calculation is repeated using the rotational line structure rather than effective band absorption.…”