Infrared emission from hydroxyl has been observed in several comets via high-resolution infrared spectroscopy. The principal excitation mechanism for this emission is single-step photolysis of H2O, terminating in OH fragments that are both vibrationally and rotationally excited. Recently reported comet data provide quantitative measures of the rotational distribution of OH*[X2Π; v' = 1] for J' < 17.5. The measured distributions of relative g-factors for OH "prompt" emission, and especially the ratios of the Π(A'') and Π(A') Λ-doubling components, are remarkably similar for comets C/2000 WM1 (LINEAR) and C/2004 Q2 (Machholz). We discuss how these results complement ab initio theoretical studies of water dissociation and those done in terrestrial laboratories.
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Bonev et al. (2006) studied this question.
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