Computational Study of the Reactions of Interstellar Molecules: CH2 Reacting with HCNO and HNCO

Abstract

Association reactions among small molecules known to exist in the interstellar medium are interesting for theories on the origins of life. A screening of thousands of reactions, using machine learning estimates of energy barriers, identified the reaction of CH2 with HCNO and HNCO as particularly interesting. We report reaction mechanisms, including energies of transition states and products, computed with density functional theory and coupled cluster theory. The lowest energy pathway on the triplet ground state surface of CH2 + HNCO has a barrier of 11 kcal/mol and produces CH2(CO)NH. Singlet CH2 is 9 kcal/mol above the ground state. It can react with HCNO or HNCO without barrier giving four products: CH2NCHO, N-methyleneformamide, the thermodynamically favoured product; NHCHCHO; NHCHOCH; and (CH2OC)NH, oxiran-2-ylazanide. If triplet to singlet crossing occurs, an upper bound of roughly 10 kcal/mol is implied for the barrier to formation of these four products.