Theoretical study on the mechanism of the HO2 plus NH2 reaction

The singlet and triplet potential surfaces of the HO2 + NH2 reaction have been investigated at the CCSD (T)//B3LYP/6-311++G (3df, 3pd) level. On the singlet potential surface, the most favorable association way starts with a barrierless addition of the HO2 to NH2 leading to HOO–NH2 (1im2 and 1im3). The product of OH and NH2O should be the major product, which obtained by a direct dissociation of the adduct 1im3 without an exit barrier. But on the triplet potential surface, DFT calculations reveal the reaction mechanism to be mainly a barrierless addition of HO2 to NH2 leading to an intermediate OOH–NH2 (3im1), and then the adduct 3im1 goes through an H transfer forming the product of NH3 and O2. The calculations show that the reaction should be taken place both on the singlet and triplet potential surface.