Mechanisms of glycine formation from aminoacetonitrile in space.

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