A molecular line survey of the candidate massive Class 0

We have carried out a molecular line survey of the candidate massive protostar IRAS 23385+6053, covering a 27.2 GHz frequency range in the 330–360 GHz atmospheric window. We detected 27 lines originating from a total of 11 species. Over a third of the identified molecular lines are from the asymmetric top molecule methanol (CH3OH). We did not detect any emission from high-excitation lines or typical hot core tracers (e.g. CH3CN, HCOOCH3). We derive a rotation temperature and column density from the methanol emission and estimate lower limits to the beam-averaged column density of the remaining lines. Upper limits to the beam-averaged column density of selected species were determined from the non-detection of their rotation lines. We rule out the presence of a hot molecular core associated with IRAS 23385+6053 by a combination of the non-detection of CH3CN emission and a simple bolometric luminosity approach. The molecular inventory and chemistry of IRAS 23385+6053 are contrasted to that of more evolved massive star-forming regions and the abundances predicted by recent time-dependent chemical models. The physical and chemical nature of IRAS 23385+6053 is shown to be consistent with that immediately prior to the hot molecular core stage.