EXCITATION OF THE LOW-LYING VIBRATIONAL LEVELS OF H2O BY O(P-3) AS MEASURED ON SPACELAB-2

The data from the infrared telescope (IRT), which was flown on space s huttle Challenger Spacelab 2 mission (July 1985), were originally repo rted by Koch et al. (1987) as originating from near orbital emissions, primarily H2O In this study, analysis of this data was extended to de termine the collisional cross sections for the excitation of the low l ying vibrational levels of H2O, present in the orbiter cloud, by atmos pheric O(P-3). The evaluation of the contribution to the measured sign al from solar excitation and ram O excitation of outgassing H2O permit s the determination of the H2O column density and the excitation cross section of the (010) level at an O(P-3) velocity of similar to 7.75 k m/s. Contributions to the radiation in the 1.7-3.0 mu m band by transi tions from the (100), (001); and multiquantum excited levels are discu ssed. The findings of the study are (1) the IRT data for the 4.5-9.5 m u m and the nighttime data for the 1.7-3.0 mu m sensors are consistent with being explained by collision excitation of H2O by O(P-3), (2) di urnal variations of 4.5-9.5 mu m intensities follow the model predicte d O density for a full orbit, (3) daytime increases in the H2O cloud d ensity were not evident, (4) the cross sections for the collisional ex citation process are derived and compared to values computated by John son (1986) and Redmon et al. (1986), (5) theoretical investigation sug gests >60% of the radiation from H2O is a result of multiphoton emissi on resulting from collisional multiquanta excitation, and (6) the larg e daytime increase in the 1.7-3.0 mu m intensity data suggests that Of may likely be instrumental in producing excited H2O+ through charge e xchange.