Theoretical study on the gas phase reaction of CH2O + NH3: the formation of CH2O⋯NH3, NH2CH2OH, or CH2NH + H2O

Abstract

The gas phase reaction between CH₂O and NH₃ is an important reaction in cold interstellar clouds, combustion chemistry and organic chemistry. In this study, the stationary point on the potential energy surfaces (PESs) for the CH₂O + NH₃ reaction was computed at the CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd) level. The temperature- and pressure-dependent rate constants were computed using advanced kinetic models, including microcanonical variational transition state theory and Rice–Ramsperger–Kassel–Marcus (RRKM)/master equation (ME) techniques. Our result predicts that the CH₂O + NH₃ reaction forms a collisionally thermalized CH₂O⋯NH₃ complex with respect to thermal unimolecular dissociation and the other products, i.e., NH₂CH₂OH and CH₂NH + H₂O, are negligible under atmospheric conditions. The calculated atmospheric lifetime of the CH₂O⋯NH₃ complex is ∼17 min, which suggests that the CH₂O⋯NH₃ complex can react with other atmospheric species. The results also suggest that the formation of CH₂NH and H₂O from the Strecker's process is negligibly small under all the conditions studied here. The decay rate of CH₂O + NH₃ (5.1 × 10⁻⁴ s⁻¹ at 1500 K) suggests that aminomethanol (NH₂CH₂OH) is likely to occur in the high-temperature combustion of biomass burning, but the rate of formation of NH₂CH₂OH is negligible under atmospheric conditions. The predicted atmospheric lifetime (∼4 days) of NH₂CH₂OH in the presence of the OH radical suggests that further reactions with other atmospheric species are possible. The formation of the NH₂CHOH radical from the reaction OH + NH₂CH₂OH can lead to carcinogenic products, such as nitrosamines, acetamide, hydrocycnic acid, NH₂ and CO₂.