Ground state potential energy surface of methanimine plus 3NH reaction: Rates of atmospheric reactions and validated mechanisms

Abstract

Methanimine (H2CNH) and imidogen (NH) are well known interstellar species and also are essential for biomolecules. In this work, the elementary reactions of H2CNH + 3NH are studied on the triplet ground state of the potential energy surface at the atmospheric conditions. Thermodynamic (enthalpy, free energy, and entropy in the standard condition) and kinetic (rate constant) parameters are computed by using the DFT-M06-2X, MP2, and CCSD(T) methods in connection with the aug-cc-pVTZ basis set. For all pathways, the rate constants were calculated in the temperature range 300–3000 K and at the atmospheric pressure by using the conventional transition state and RRKM theories at the M06-2X/aug-cc-pVTZ level. The addition processes that lead to forming the stable adducts, are thermodynamically favorable, while the hydrogen transfer processes are kinetically favorable. So, the H2CN + NH2 and trans-HNCH + NH2 adducts are kinetically main product channels, and production of the H3CNNH is the main reaction in the thermodynamic viewpoint.