Computational studies on the gas phase reaction of methylenimine (CHNH) with water molecules.

In this work, we used quantum chemical methods and chemical kinetic models to answer the question of whether or not formaldehyde (CHO) and ammonia (NH) can be produced from gas phase hydration of methylenimine (CHNH). The potential energy surfaces (PESs) of CHNH + HO → CHO + NH and CHNH + 2HO → CHO + NH + HO reactions were computed using CCSD(T)/6-311++G(3d,3pd)//M06-2X/6-311++G(3d,3pd) level. The temperature-and pressure-dependent rate constants were calculated using variational transition state theory (VTST), microcanonical variational transition state theory [Formula: see text] and Rice-Ramsperger-Kassel-Marcus/master equation (RRKM/ME) simulations. The PES along the reaction path forming a weakly bound complex (CHNH⋯HO) was located using VTST and [Formula: see text]VTST, however, the PES along the tight transition state was characterized by VTST with small curvature tunneling (SCT) approach. The results show that the formation of CHNH + HO → CHNH⋯HO is pressure -and temperature-dependent. The calculated atmospheric lifetimes of CHNH⋯HO (~ 8 min) are too short to undergo secondary bimolecular reactions with other atmospheric species. Our results suggest that the formation of CHO and NH likely to occur in the combustion of biomass burning but the rate of formation CHO and NH is predicted to be negligible under atmospheric conditions. When a second water molecule is added to the reaction, the results suggest that the rates of formation of CHO and NH remain negligible.