We conducted survey observations of a glycine precursor, methanimine, or methylenimine (CH 2 NH), with the Nobeyama Radio Observatory 45 m telescope and the Sub-Millimeter Radio telescope toward 12 high-mass and two low-mass star-forming regions in order to increase the number of known CH 2 NH sources and to better understand the characteristics of CH 2 NH 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 toward the other sources. Our hydrogen recombination line and past studies suggest that CH 2 NH-rich sources have less (this mean not so evolved) evolved H II regions. The lower destruction rates from UV flux from the central star would contribute to the high CH 2 NH abundances toward 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 being the product of thermal evaporation from dust surfaces.

The study of the chemical evolution of glycine in the interstellar medium is one of challenging topics in astrochemistry. Here, we present the chemical modeling of glycine in hot cores using the state-of-the-art three-phase chemical model NAUTILUS, which is focused on the latest glycine chemistry. For the formation process of glycine on the grain surface, we obtained consistent results with previous studies that glycine would be formed via the reactions of COOH with CH 2 NH 2 . However, we will report three important findings regarding the chemical evolution and the detectability of interstellar glycine. First, with the experimentally obtained binding energy from the temperature programmed thermal desorption (TPD) experiment, a large proportion of glycine was destroyed through the grain surface reactions with NH or CH 3 O radicals before it fully evaporates. As a result, the formation process in the gas phase is more important than thermal evaporation from grains. If this is the case, NH 2 OH and CH 3 COOH rather than CH 3 NH 2 and CH 2 NH would be the essential precursors to the gas phase glycine. Secondly, since the gas phase glycine will be quickly destroyed by positive ions or radicals, early evolutionary phase of the hot cores would be the preferable target for the future glycine surveys. Thirdly, we suggest the possibility that the suprathermal hydrogen atoms can strongly accelerate the formation of COOH radicals from CO 2 , resulting in the dramatic increase of formation rate of glycine on grains. The efficiency of this process should be investigated in detail by theoretical and experimental studies in the future.

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.