Theoretical Investigation of the Reaction of Imidogen with Fulminic Acid.

The mechanism of the reaction of imidogen (NH) with fulminic acid (HCNO) has been investigated theoretically using the multiconfigurational self-consistent-field theory (MCSCF), multireference Rayleigh-Schrodinger perturbation theory (RSPT2), and coupled cluster theory (CC) along with the complete basis set extrapolations (CBS). The calculations show that the NH + HCNO reaction takes place via an N → C addition mechanism predominantly by surmounting a small barrier (ca. ∼3 kcal/mol). The adduct is HC(NH)NO in the triplet state with an exothermicity of more than 60 kcal/mol. The subsequent C-N cleavage, which is nearly barrierless, leads to HCNH and NO as the final products. This represents the most energetically favorable product channel of the title reaction. The channels leading to HCN, HNC, HNO, or HON via O- or H-migration mechanisms involve higher barriers and thus are negligible. The singlet-triplet crossing has been investigated as well for the HCNH + NO product channel by locating the conical interactions. Using transition state theory, the rate constants were predicted as a function of temperatures. It is suggested that the NH + HCNO reaction might be an alternative source for the NO regeneration under the combustion conditions. This calculation is useful to simulate experimental investigations of the NH + HCNO reaction.