Effect of atomic oxygen on the N₂vibrational temperature in the lower thermosphere

Abstract

The relative significance of different physical processes that determine the state of vibrational excitation of the molecular constituents in the lower thermosphere has recently been discussed by Bauer et al. [1971]. Walker et al. [1969] have performed detailed calculations of the vibrational temperature of N• in this region under both normal and disturbed atmospheric conditions. Results of a similar nature are described by Bauer et al. [1971] and Kummler and Bortner [1972] and are based on a theoretical investigation by Jamshidi [1971]. The state of vibrational excitation of N• has special importance because of its influence on such atmospheric processes. as ionospheric loss rates, the heating of the ambient electron gas, infrared emission from NO, CO, and CO• resulting from near-resonance vibrational energy transfer, and the like [Walker et al., 1969; Walker, 1968; Degges, 1971]. The purpose of this letter is to demonstrate the special importance of the quenching of vibrationally excited nitrogen N• • by atomic oxygen in a direct vibration-to-translation energy transfer process in the lower thermosphere. Atomic oxygen is a major constituent in this region of the atmosphere, and recent model atmospheres [Jacchia, 1971] suggest an increase in its concentration relative to earlier models. However, its ultimate importance with regard to N2 • depends primarily on the magnitude of the energy transfer rate constant. Until recently the only information on this rate was obtained by Breshears and Bird [1968] for kinetic temperatures in excess of 3000øK. The analysis of Walker et al. [1969] neglected this N• • loss process; however, Jamshidi [1971] did investix Now at University of Texas at Dallas, Dallas, Texas 75230.

The ultraviolet dayglow at solar maximum: 1. Far UV spectroscopy at 3.5 Å resolution

“…The laboratory work of Holland [1969] and Ajello [1970] is consistent with all of the molecules initially being in the v"= 0 state. A Boltzmann ground state distribution with a 900øK vibrational temperature, which is consistent with published values [Breig et al, 1973], would change the level populations by less than 10%. This would be insufficient to produce the observed effect.…”

Vibrational temperature and molecular density of thermospheric nitrogen measured by rocket-borne electron beam induced luminescence

“…The vibrational population of E region N,(X•2;g+), an atmospheric parameter heretofore not investigated in situ, is of aeronomic interest for its role in the energy partition of the atmosphere and in an increasing number of known atmospheric processes [Kummler and Bortner, 1972]. The generally slow nature of the reactions in which vibrational quanta are lost from the homonuclear infrared inactive nitrogen molecule has resulted in several [Walker eta/., 1969;Varnum, 1972;Breig et al, 1973;Jamshidi et al, 1973] recent estimates that nitrogen vibrational temperature may significantly exceed the kinetic temperature at altitudes greater than 100 km. Aeronomically important known production and loss processes for vibrationally excited N, and N,* are summarized in Table 1.…”

Effects of soft electron precipitation on the distribution of vibrational energy of N2

“…Thus it is necessary to know the distribution of vibrational energy of N• in order to specify precisely the rate for the O + + N• reaction. Several theoretical studies of the vibrational temperature and its diurnal variation resulting from chemical reactions and photoelectron collisions in the mid-latitude ionosphere have been made [Walker, 1968;Walker et al, 1969;Kummler and Bonner, 1972;Varnum, 1972;Breig et al, 1973]. Schunk and Hays [1971] studied the response to auroral precipitation of N• vibration in the lower thermosphere, and Schunk and Banks [1975] have suggested that vibrationally excited N• may be transported from the auroral oval to lower latitudes to produce the mid-latitude F region electron trough.…”