Ab initio study on the spin-forbidden reaction HNO( 1A′)+H 2→NH( 3Σ)+H 2O

Abstract

The spin-forbidden reaction HNO( 1A′)+H 2→NH( 3Σ)+H 2O was investigated by ab initio and DFT calculations. We first investigated the HNO+H 2→NH( 1Δ)+H 2O singlet reaction and found three possible pathways with significantly high reaction barriers. The lowest barrier height was calculated to be 193.3 kJ/mol at the MP4/cc-pVTZ//MP2/cc-pVTZ level. A crossing between the singlet and triplet potential energy surfaces occurs at the product region after which the NH 2OH complex is formed. The energy at the crossing point was estimated to be lower than the barrier height of the formation of the NH 2OH complex. It is then concluded that the reaction of HNO+H 2→NH( 3Σ)+H 2O proceeds by the addition of H atom of the H 2 molecule to the N atom of HNO molecule and forms the NH 2OH complex through two transition states and an intermediate on the singlet PES, and finally crosses with the triplet surface.