Rocket-borne spectroscopic measurements in the ultraviolet aurora: Nitrogen Vegard-Kaplan bands

Abstract

The ultraviolet spectrum of an aurora was measured with a spectrometer that was carried by rocket into an IBC I+ aurora. Altitude profiles of the band emissions from the Vegard-Kaplan and second positive systems of N2 were obtained. Consideration of all the excitation processes of the N2 triplet states shows that the production of the A3Σu+ state is proportional to the production of the C3Πu state. The volume emission rate profile of the Vegard-Kaplan system deduced from the column emission rate indicated that the system was quenched. Comparison of the volume emission rate of the second positive and Vegard-Kaplan systems gives quenching rates for the υ′=0 and 1 levels of the A3Σu+ state, which vary smoothly from 100 sec−1 at 100 km to 0.3 sec−1 at 220 km. At high altitudes the most likely quenching agent is atomic oxygen, with molecular oxygen becoming important below 120 km. With the use of a model atmosphere, the coefficients for the quenching of the υ′=0 and 1 levels of the A3Σu+ state of N2 by atomic oxygen are calculated to be 9×10−11 and 1.1×10−10 cm3 sec−1, respectively. The ratio of quenching coefficients for atomic oxygen and molecular oxygen is 4.2. The rotational temperature of the A3Σu+ state increases with altitude.