Mechanism of the radical reaction between C₃H₅ and NO

Although the rate constants of the C₃H₅+NO reaction were determined more than 20 years ago, no theoretical investigations have been reported up to now. In present paper, we performed a detailed mechanistic study on this reaction by constructing a singlet potential energy surface [C₃H₅NO] at the CCSD(T)/6-311G(d,p) //B3LYP/6-311G(d,p) level. The most favorable entrance channel is the direct radical-radical combination to form isomer H₂CCHCH₂NO m1 (-23.44 kcal/mol). The calculated zero barrier is consistent with the determined high rate constant at room temperature. Except dissociation back to the reactants, the further conversion of m1 needs to overcome the transition states with energies being at least 23 kcal/mol higher than the reactant. This is indicative of a distinct pressure dependence of the rate constants, which is also consistent with the experimental finding. The energetically very low-lying products P₁ CH₂CHCN+H₂O (-71.36 kcal/mol), P₂ CH₃CHO+HCN (-72.61 kcal/mol) and P₃ CH₃CHO+HNC (-57.55 kcal/mol), however, cannot be reached kinetically.