Theoretical study on the reaction mechanism of NH2- with O_2 (a~1Δ_g)

摘要

A detailed theoretical study of the potential energy surface of poorly understood ion - molecule reaction of NH_2~- and O _2 (a~1Δ_g) is explored at the density functional theory B3LYP/6-311++G(d,p), ab initio of QCISD/6-311++G(d,p) and CCSD(T)/6-311++G(3df, 2pd) (single-point) theoretical levels for the first time. It is shown that there are six total possible products from P_1 to P_6 on the singlet potential energy surface. Among these, the charge-transfer product P_1 (NH_2 + O_2~-) is the most favorable product with predominant abundances, whereas P_4 (NO~- + H_2O) and P_2 (HNO + OH~-) may be the second and third feasible products followed by the almost neglectable P_3 (NO_2~- + H_2), while P_5 (c-NO_2~- + H_2) and P _6 (ONO- + H_2) will not be observed due to their either high barriers or being secondary products. The present theoretical study points out that besides P_1 (NH_2 + O_2~-) and P_2 (HNO + OH~-), P_4 (NO ~- + H_2O) should be also observed, which is different from the previous experiment study by Anthony Midey et al. in 2008. In addition, almost all of the reaction pathways to products are exothermic and the reaction rate should be very fast since the reaction barriers are very low except for P_5 (c-NO_2~- + H_2) which is in agreement with the measured total reaction rate constant k ≥ 9.0×10~(-10) cm~3s~(-1) at 300 K in the experiment study. It is expected that the present theoretical study may be helpful for the understanding of the reaction mechanism related to NHX ~-, NX_2~-, PHX~-, and PX _2~- (X ≥ H, F, and Cl).