In the Orion Molecular Cloud, the conditions needed to excite the higher rotational transitions of OH into emission are usually associated with gas that has been compressed and heated by the passage of a shock wave. According to the shock models of Draine, Roberge, and Dalgarno (1983), up to several percent of the preshock O2 and O are converted into OH in the ≡103K post-shocked gas. Assuming that oxygen is present in its cosmic abundance in the preshock gas, this implies a possible column density of hot OH of between about 4×1016 and 1017cm-2.
Masers, Molecules, and Mass Outflows in Star Formation Regions
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