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 C H2NH + H2O -> CH2O ->+NH3 and CH2NH + 2H(2)O -> 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 (mu VTST) and Rice-Ramsperger-Kassel-Marcus/master equation (RRKM/ME) simulations. The PES along the reaction path forming a weakly bound complex (CH2NH center dot center dot center dot H2O) was located using VTST and mu 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 (similar to 8 min) are too short to undergo secondary bimolecular reactions with other atmospheric species. Our results suggest that the formation of C H2O and N H-3 likely to occur in the combustion of biomass burning but the rate of formation C H2O and N H-3 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 C H2O and N H-3 remain negligible.