Formation of the glycine isomer glycolamide (NH₂C(O)CH₂OH) on the surfaces of interstellar ice grains: Insights from atomistic simulations

Context . Syn -glycolamide, a glycine isomer, has recently been detected in the G+0.693-0.027 molecular cloud. Investigations into its formation in the interstellar medium could offer insights into synthetic routes leading to glycine in prebiotic environments. Aims . Quantum chemical simulations on glycolamide (NH 2 C(O)CH 2 OH) formation on interstellar ice mantles, mimicked by a water ice cluster model, are presented. Methods . In this paper, we modeled glycolamide synthesis considering a stepwise process: the coupling between formaldehyde (H 2 CO) and the radical of formamide (NH 2 CO • ) occurs first, forming the glycolamide precursor NH 2 C(=O)CH 2 O • , which is then hydrogenated to give anti -glycolamide. We hypothesize that anti -to- syn interconversion occurs in conjunction with glycolamide desorption from the ice surface. Results . The reaction barrier for NH 2 C(O)CH 2 O • formation varies from 9 to 26 kJ mol −1 , depending on surface binding sites. Kinetic studies indicate that this reaction step is feasible in environments with a T > 35 K, until desorption of the reactants. The hydrogenation step leading to anti -glycolamide presents almost no energy barrier due to the easy H atom diffusion toward the NH 2 C(O)CH 2 O • intermediate. However, it competes with the extraction of an H atom from the formyl group of NH 2 C(O)CH 2 O • , which leads to formyl formamide, NH 2 C(O)CHO, and H 2 . Nonetheless, according to our results, anti -glycolamide formation is predicted to be the most favored reactive channel.