Infrared OH prompt emission as a proxy of water production in comets:: Quantitative analysis of the multiplet near 3046 cm-1 in comets C/1999 H1 (Lee) and C/2001 A2 (LINEAR)

We report quantitative measurements of OH vibrational prompt emission in comets C/1999 H1 ( Lee) and C/2001 A2 ( LINEAR) based on high-dispersion infrared spectra acquired at the Keck Observatory atop Mauna Kea, Hawaii. Effective g-factors for four OH lines near 3046 cm(-1) (in the 1-0 band) were obtained from simultaneous detections of OH and H2O. The measured spatial distribution of this OH "quadruplet'' traces that of H2O, as expected if the excited OH is produced directly by water photolysis. These results establish OH prompt emission as an alternative (and convenient) proxy for water in comets. Possible limitations to the approach are discussed. Extension to other OH multiplets in the L band will permit direct comparison with theoretical models for the rotational population distribution of the free OH radicals produced by H2O photolysis in cometary atmospheres.