A search for vibrationally excited H2O at 68 GHz

Water vapor may be one of the most abundant constituents of shocked molecular clouds. The nonequilibrium distribution of population among its rotational energy states requires the observation of a multiplicity of transitions to constrain its abundance and excitation state. Flux limits are presented for emission due to the (010) 4(14) - 3(21) rotational transition of ortho-H2O at 67.804 GHz in several nebular and stellar sources. Upper limits for a beam-averaged column density of H2O in its nu2 vibrational manifold are derived for Orion BN-KL. Constraints placed by these observations on an internal source of infrared radiation in the Orion shock are discussed.