2018ApJ...863...51S

The study of the chemical evolution of glycine in the interstellar medium is one of the 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 and the detectability of interstellar glycine. First, with the experimentally obtained binding energy from the temperature-programmed desorption (TPD) experiment, a large proportion of glycine was destroyed through the grain surface reactions with NH or CH₃O radicals before it fully evaporated. 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. Second, since the gas-phase glycine will be quickly destroyed by positive ions or radicals, the early evolutionary phase of the hot cores would be the preferable target for the future glycine surveys. Third, we suggest the possibility that the suprathermal hydrogen atoms can strongly accelerate the formation of COOH radicals from CO₂, 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.