Theoretical investigation of the potential energy surface for the reaction of NO3 with H

Adducts and transition states have been located in ab initio MP2/6-311G** calculations on both the singlet and triplet potential energy surfaces for the reaction NO3 + H bar right arrow NO2 + OH. Reaction on the singlet surface is shown to be improbable because the calculated enthalpy of activation for the initial step is about 350 kJ mol(-1). On the triplet surface an H ... ONO2 adduct is formed exothermically without any activation barrier. In the adduct, the NO3 moiety is non-planar. Reaction on the triplet surface to NO2 + OH can then occur via a transition state lying 16 kJ mol(-1) above the energy of the adduct.