Survey Observations of a Possible Glycine Precursor, Methanimine
  (CH$_2$NH)
  We conducted survey observations of a glycine precursor, methanimine or
methylenimine (CH$_2$NH), with the NRO 45 m telescope and the SMT telescope
towards 12 high-mass and two low-mass star-forming regions in order to increase
number of CH$_2$NH sources and to better understand the characteristics of
CH2NH sources. As a result of our survey, CH$_2$NH was detected in eight
sources, including four new sources. The estimated fractional abundances were
~10$^8$ in Orion KL and G10.47+0.03, while they were ~10$^9$ towards the other
sources. Our hydrogen recombination line and past studies suggest that
CH$_2$NH-rich sources have less evolved HII regions. The less destruction rates
by UV flux from the central star would be contributed to the high CH$_2$NH
abundances towards CH$_2$NH-rich sources. Our gas-grain chemical simulations
suggest that CH$_2$NH is mostly formed in the gas-phase by neutral-neutral
reactions rather than the product of thermal evaporation from the dust
surfaces.
