LAUSR

ABSTRACT The potential-energy surfaces of the amino radical (NH2) with IO reaction have been studied at the CCSD(T)/cc-pVTZ//MP2/6-311++G(d,p) level. Two kinds of pathways are revealed, namely H-abstraction and addition/elimination. Rice–Ramsperger–Kassel–Marcus theory and transition state theory are employed to calculate the overall and individual rate constants over a wide range of temperatures and pressures. It is predicted that, at atmospheric pressure with N2 as bath gas, the formation of P1 (HI + HNO) is the dominant pathways at 200–700 K, while the direct H-abstraction leading to P3 (3NH + HOI) takes over the reaction at a temperature above 700 K. At the high-pressure limit, IM1 [IONH2] formed by collisional stabilisation is dominant at 200–700 K; the direct H-abstraction resulting in P3 (3NH + HOI) plays an important role at higher temperatures. However, the total rate constants are independence on the pressure; however, the individual rate constants are sensitive to pressure. The atmospheric lifetime of NH2 in IO is around one week. TD-DFT computations imply that IM1 [IONH2], IM1A [IONH2′], IM2 [IN(H2)O], IM3 [OINH2], IM4 [HOINH], tra-IM5 [tra-HON(H)I] and cis-IM5 [cis-HON(H)I] will photolyze under the sunlight. GRAPHICAL ABSTRACT