A. OH. The near-infrared band emissions of OH have been studied extensively since their discovery by Meinel in 1950. They are a prominent feature of both the nightglow and the dayglow. The OH airglow is found everywhere over the globe, and its morphology has been described by Jones (1973), among others. The principal mesospheric excitation mechanism is the reaction (Meinel, 1950) where vibrational states up to v = 9 are populated. Through detailed calculations, it is found that following the H + 0^ reaction, the number of photon emitted in the vibrational sequences Av = 1, 2, 3, 4 are roughly 2, 3, 0.04, 0.005, respectively. Although there is some controversy over the degree of rotational equilibrium of the nightglow OH emission, Krassovsky et al. (1977) have presented evidence showing that the rotational temperatures of different vibrational bands are roughly equal when viewed simultaneously to within an experimental precision of 10-20 K, and correspond to ambient temperatures within this same precision. Thus, high resolution OH emission spectra may be utilized to determine (crudely) air temperatures in the upper mesosphere, but (with current instrumentation) only at night when background light levels are low. When water is released in the thermosphere, charge exchange with 0+ produces H20+, which, upon recombination with electrons, generates hydroxyl radicals. The degree of vibrational and electronic excitation of the OH formed in this way is unknown, but should be determined. In this regard, M. Pongratz (private communication) notes that very little OH vibrational emission in the (9,4) and (5,1) bands was observed following the LAGOPEDO F- region water release. This implies little excitation of the v = 9 and v = 5 OH vibrational levels. The concentration of hydrogen atoms in the atmosphere is directly related to the total amount of hydrogen in all forms residing there. Above 80 km, injected water vapor will be decomposed by sunlight and ion-molecule reactions; the resultant hydrogen is partitioned between H and H2, with some of the H-atoms being continuously recycled betwen H and OH. Thus, the spatial and temporal changes in airglow intensity caused by the passage of a rocket will depend on the amount of water vapor released, on its rate of dispersal and removal as against decomposition, and its photochemical partitioning into H, OH, and H2« (In addition, it must be noted that in typical H2-O2 rocket motors, perhaps 25% of the hydrogen is emitted at H2 rather than as H2O.) The major impact of enhanced OH emission rates may be their influence on the mesopause temperature and, consequently, their possible connection with noctilucent cloud formation (Chenurnoy and Charina, 1977). Interestingly, Moreels and Herse (1977) have observed wave—like structures in OH emision patters that match some noctilucent cloud patterns. B. Singlet oxygen. The 0(^D) 630 nm red line and the 0(^S) 557.7 nm green line are well-studied emissions whose morphology is fairly well established. The lines can be excited photochemically (O2 + hv, 0 + 0 + 0) and through ion neutralization reactions, and normally originate about 90 km.
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