Computational Study of the Mechanism, Reaction Rate and Thermochemistry of Atmospheric Oxidation of Methylamine with Singlet Oxygen

Abstract

The reaction of CH₃NH₂ with O₂ on the singlet potential energy surfaces (PES) was carried out using the B3LYP, CCSD(T) and G3B3 theoretical approaches along with 6-311++G(3df,3pd) basis set. The suggested mechanism for the title reaction consists of one pre-reactive complex. From the pre-reactive complex, nine types of products, CH₂NH+H₂O₂, CH₃NH+OOH, NH₂CHO+H₂O, CH₂NHO+H₂O, NH₃+HCOOH, CH₂NH+H₂+O₂, HCHO+NH₂OH, CH₂NH₂+HOO and CH₂NH+H₂OO are obtained. Six adducts are found to be thermodynamically stable with the negative value in Gibbs free energy and three products are not stable with positive value in Gibbs free energy at standard condition. NH₂CHO+H₂O and NH₃+HCOOH with more free energy values are the thermodynamic products. CH₂NH and H₂O₂ are the major products for the title reaction. The rate constant for the major pathway is calculated in the temperature range of 300-1000 K at atmospheric pressure at the B3LYP//6-311++G(3df,3pd) level of computation.