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.

Two figures are the Energy diagrams for the HO2 + NH2 reaction paths on the singlet and triplet surface. As shown in figures, 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.Highlight► The singlet and triplet potential surfaces of the HO2 + NH2 reaction were studied. ► OH and NH2O are the major products on the singlet potential surface. ► But on the triplet potential surface, the products of NH3 and O2 will be dominant. ► The reaction should be taken place both on the singlet and triplet PESs.