The Difference in Abundances between N-bearing and O-bearing Species in
  High-Mass Star-Forming Regions
  The different spatial distributions of N-bearing and O-bearing species, as is
well known towards Orion~KL, is one of the long-lasting mysteries. We conducted
a survey observation and chemical modeling study to investigate if the
different distributions of O- and N-bearing species are widely recognized in
general star-forming regions. First, we report our observational results of
complex organic molecules (COMs) with the 45~m radio telescope at the Nobeyama
Radio Observatory towards eight star-forming regions. Through our spectral
survey ranging from 80 to 108~GHz, we detected CH$_3$OH, HCOOCH$_3$,
CH$_3$OCH$_3$, (CH$_3$)$_2$CO, CH$_3$CHO, CH$_3$CH$_2$CN, CH$_2$CHCN, and
NH$_2$CHO. Their molecular abundances were derived via the rotation diagram and
the least squares methods. We found that N-bearing molecules, tend to show
stronger correlations with other N-bearing molecules rather than O-bearing
molecules. While G10.47+0.03 showed high fractional abundances of N-bearing
species, those in NGC6334F were not so rich, being less than 0.01 compared to
CH$_3$OH. Then, the molecular abundances towards these sources were evaluated
by chemical modeling with NAUTILUS three-phase gas-grain chemical code. Through
the simulations of time evolutions for the abundances of COMs, we suggest that
observed correlations of fractional abundances between COMs can be explained by
the combination of the different temperature structures inside the hot cores
and the different evolutionary phase. Since our modeling could not fully
explain the observed excitation temperatures, it is important to investigate
the efficiency of grain surface reactions and their activation barriers, and
the binding energy of COMs to further promote our understanding.
