Computational studies on the gas phase reaction of methylenimine (CH₂NH) with water molecules

In this work, we used quantum chemical methods and chemical kinetic models to answer the question of whether or not formaldehyde (CH₂O) and ammonia (NH₃) can be produced from gas phase hydration of methylenimine (CH₂NH). The potential energy surfaces (PESs) of CH₂NH + H₂O → CH₂O + NH₃ and CH₂NH + 2H₂O → CH₂O + NH₃ + H₂O 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 (CH₂NH⋯H₂O) 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 CH₂NH + H₂O → CH₂NH⋯H₂O is pressure -and temperature-dependent. The calculated atmospheric lifetimes of CH₂NH⋯H₂O (~ 8 min) are too short to undergo secondary bimolecular reactions with other atmospheric species. Our results suggest that the formation of CH₂O and NH₃ likely to occur in the combustion of biomass burning but the rate of formation CH₂O and NH₃ 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 CH₂O and NH₃ remain negligible.