Abstract
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 (mu VTST) 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 muVTST, 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.
Highlights
The alkylamines especially methylamine is emitted to the atmosphere from various sources such as biogenic, oceanic, anthropogenic, animal husbandry, marine emissions, biomass burning, chemical manufacturing and carbon capture storage (CCS) technologies[1]
We have proposed the formation of CH2O⋯NH3, NH2CH2OH and CH2NH from CH2O + NH3 reaction
Our group has predicted the rate constants for H O2 + CH2NH reaction using ab initio// density functional theory (DFT) methods coupled with microcanonical variational transition state t heory[22]
Summary
The alkylamines especially methylamine is emitted to the atmosphere from various sources such as biogenic, oceanic, anthropogenic, animal husbandry, marine emissions, biomass burning (forest vegetation, savannah grass, firewood and agricultural wastes), chemical manufacturing and carbon capture storage (CCS) technologies[1]. Gas-phase theoretical models of the methylenimine chemistry in hot protostellar cores are required to explain the formation of substantially larger organics under interstellar c onditions[26]. These molecules can undergo gas-phase reactions to form more complex species such as amino acids, sugars, and other biologically important molecules surface. In 2015, Ali and Barker predicted the rate constants for the OH + CH2NH reaction using ab initio//DFT methods coupled with variational transition state theory[21]. Our group has predicted the rate constants for H O2 + CH2NH reaction using ab initio// DFT methods coupled with microcanonical variational transition state t heory[22]. The overall reaction rate constants are smaller[23,24]
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