Complex molecules in W51 North region
  We present Submillimeter Array (SMA) molecular line observations in two 2
GHz-wide bands centered at 217.5 and 227.5 GHz, toward the massive star forming
region W51 North. We identified 84 molecular line transitions from 17 species
and their isotopologues. The molecular gas distribution of these lines mainly
peaks in the continuum position of W51 North, and has a small tail extending to
the west, probably associated with W51 d2. In addition to the commonly detected
nitrogen and oxygen-bearing species, we detected a large amount of transitions
of the Acetone (CH$_3$COCH$_3$) and Methyl Formate (CH$_3$OCHO), which may
suggest that these molecules are present in an early evolutionary stage of the
massive stars. We also found that W51 North is an ethanol-rich source. There is
no obvious difference in the molecular gas distributions between the
oxygen-bearing and nitrogen-bearing molecules. Under the assumption of Local
Thermodynamic Equilibrium (LTE), with the XCLASS tool, the molecular column
densities, and rotation temperatures are estimated.
  We found that the oxygen-bearing molecules have considerable higher column
densities and fractional abundances than the nitrogen-bearing molecules. The
rotation temperatures range from 100 to 200 K, suggesting that the molecular
emission could be originated from a warm environment.
  Finally, based on the gas distributions, fractional abundances and the
rotation temperatures, we conclude that CH$_3$OH, C$_2$H$_5$OH, CH$_3$COCH$_3$
and CH$_3$CH$_2$CN might be synthesized on the grain surface, while gas phase
chemistry is responsible for the production of CH$_3$OCH$_3$, CH$_3$OCHO and
CH$_2$CHCN.
