The 0( D) atoms give rise to the 630 and 636.4 nm emissions; the 0(^S) gives rise to the green 557.7 nm line. However, reactions (2a,b) are improbable paths for the reaction of H?0+ with electrons. The most likely path is (Wadt, et al., 1977). The rates of (2a) and (2b) together are expected to be less than 10% as large as the rate of (2c). The OH radicals produced in (2c) may be vibrationally excited, giving rise to some OH band emission. However, most of the 7.5 eV of energy released in the reaction is expected to go into translation of the H atoms, (Wadt. et al., 1977). If this is the case, it should result in some local heating of the ionosphere and generation of gravity waves. However, reactions (4a,b) are expected to be improbable relative to 3 The ground state 0( P) atoms do not radiate. The energy released in the reaction is expected to go mainly into translation of the H atoms (Wadt et al., 1977). The branching ratio for the 0(1D)-producing reaction (4a) is expected to be 10 to 15%, relative to (4a) 4- (4b) + (4c). Thus, something of the order of 10% of the energy released in the recombination reactions may go into 01 airglow emissions. Another unknown fraction, between 0 and 50%, goes into OH emissions. The remainder goes into heating, gravity waves, and H atoms that escape to space. The above statements are based on theory alone. Branching ratios for the H2O + e and OH + e reactions have never been measured. It would be of great interest to obtain some experimental data, perhaps on the September 1979 HEAO—C launch. Airglow measurements were made in the 1977 Lagopedo experiments. The equipment included several narrow-band-filtered photometers, some filtered, image-intensified cameras, and an intensified spectrograph. Quantitative measurements were made at 630 nm (0CD)), 557.7 nm (0^S)), 666 nm (0H*(10-4, R-branch)), 623.4 nm (0H*(9-3)), 772 and 786 nm (OH*(9-4)), and 455.5 nm (continuum). Of these the only bands that showed enhancements attributable to airglow were 630, 557.7, and 666 nm. (Horak et al., 1978).
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