Mechanisms of glycine formation from aminoacetonitrile in space

Abstract

The potential energy surfaces for the formation of glycine (Gly) or its precursors, such as Gly radical cation and deprotonated Gly, starting from aminoacetonitrile (NH2CH2CN) or deprotonated aminoacetonitrile were determined by CBS-QB3 calculation. The reaction of NH2CH2CN + H2O+ + H2O gave mainly unwanted products other than Gly or its precursors. The reactions of NHCH2CN + 2H(2)O, NH2CHCN + 2H(2)O, or NH2CH2CN + OH + H2O, led to Gly or its precursors as one of the main products. The overall activation barriers were 229 kJ mol(-1), 216 kJ mol(-1), and 118 kJ mol(-1), respectively. A barrierless pathway for the formation of Gly from the reaction of NH2CH2CN + OH + H2O with a catalytic H2O was found, strongly suggesting that Gly can be formed thermally from NH2CH2CN and OH on icy grain surfaces in the interstellar medium.