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

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.