Keywords:Interstellar Chemistry, Chemical Evolution, Glycine
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 CH2NH2. However, we will report three important findings regarding the chemical evolution of interstellar glycine. First, with the experimentally obtained binding energy from the temperature programmed thermal desorption (TPD) experiment, large part of glycine was destroyed through the grain surface reactions with NH or CH3O 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, NH2OH and CH3COOH rather than CH3NH2 and CH2NH 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 CO2, resulting in the dramatical 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.