High-Sensitivity Observations of Molecular Lines with the Arecibo
  Telescope
  We report on one of the highest sensitivity surveys for molecular lines in
the frequency range 6.0 to 7.4 GHz conducted to date. The observations were
done with the 305m Arecibo Telescope toward a sample of twelve
intermediate/high-mass star forming regions. We searched for a large number of
transitions of different molecules, including CH3OH and OH. The low RMS noise
of our data (~5 mJy for most sources and transitions) allowed detection of
spectral features that have not been seen in previous lower sensitivity
observations of the sources, such as detection of excited OH and 6.7 GHz CH3OH
absorption. A review of 6.7 GHz CH3OH detections indicates an association
between absorption and radio continuum sources in high-mass star forming
regions, although selection biases in targeted projects and low sensitivity of
blind surveys imply incompleteness. Absorption of excited OH transitions was
also detected toward three sources. In particular, we confirm a broad 6.035 GHz
OH absorption feature in G34.26+0.15 characterized by an asymmetric
blue-shifted wing indicative of expansion, perhaps a large scale outflow in
this HII region.
