Theoretical Study On The Reaction Mechanism Of Two Atmospheric Pollutants

In recent years, atmospheric chemistry and combustion chemistry received widespread concernsfrom the experimental and theoretical scientists. A detailed theoretical study on two important chemicalreactions in atmospheric chemistry.1.The reaction mechanisms of CH3NHNH2with O(3P) and O(1D) atoms have been exploredtheoretically at the MPW1K/6-311+G(d,p), MP2/6-311+G(d,p), MCG3-MPWPW91(single-point), andCCSD(T)/cc-pVTZ(single-point) levels. The triplet potential energy surface for the reaction of CH3NHNH2with O(3P) includes seven stable isomers and eight transition states. When the O(3P) atom approachesCH3NHNH2, the heavy atoms, namely N and C atoms, are the favorable combining points. O(3P) atomattacking the middle-N atom in CH3NHNH2results in the formation of an energy-rich isomer(CH3NHONH2) followed by migration of O(3P) atom from middle N atom to H atom leading to the productP6(CH3NNH2+OH), which is one of the most favorable pathways. The estimated major productCH3NNH2is consistent with the experimental measurements. Reaction of O(1D)+CH3NHNH2presentsdifferent features as compared with O(3P)+CH13NHNH2. O(D) atom will firstly insert into C-H2, N1-H4,and N2-H5bonds barrierlessly to form three adducts, respectively. There are two most favorable pathwaysfor O(1D)+CH3NHNH2. One is that the C-N bond cleavage accompanied with a concerted H shift from Oatom to N atom (mid-N) leading to product PI(CH2O+NH2NH2), the other is that N-N bond rupture alongwith a concerted H shift from O to N1to form PIV(CH3NH2+HNO).2. The decomposition reaction of ClCH2CH2OOH has been explored theoretically. All structuresof the stationary points and harmonic vibrational frequencies are calculated at the BMK/ma-TZVP level. Inorder to obtain more accurate energetic information, higher level energy calculations are performed at theBMC-CCSD level. Totally, fifteen pathways are theoretically studied for the decomposition reaction.Fifteen pathways can be classified into two types. One is the direct bond dissociation channels includingthe O-O, C-C, C-O and C-H bond cleavage. Our calculated results show that the formation ofP9(ClCH2CH2O+OH) via O-O direct bond cleavage is dominant. The other type is elimination processcontaining H2, H2O, H2O2, CH2O, CH3Cl molecules and O-atom elimination. P9(ClCH2CH2O+OH) is the most possible reaction product. The present work may provide helpful assistance for future experimentalidentification of the product distributions and for understanding the hydroperoxide chemistry.