Ab initio study of the dissociation of formyl cyanide

The energetics of the unimolecullar dissociation of formyl cyanide, HCOCN, along three paths were examined by ab initio computations. The energy barriers for unimolecular dissociation, calculated at the QCISD(T)/6–311(3d, 3p)//QCISD/6–311(d, p) level of theory with correction for zero-point energy, are 64.04 and 62.17 kcal/mol for paths 1 and 2. The barriers for two successive steps of path 3, involving an intermediate, HCONC, which lies 13.06 kcal/mol above formyl cyanide, are 42.74 and 50.48 kcal/mol for the first and second steps. The rates of reaction along paths 1, 2 and 3 are 3.60 × 10−34, 7.61 × 10−33 and 1.59 × 10−33 s−1 at 300 K, and 7.11 × 10−7, 2.48 × 10−6 and 2.20 × 10−6 s−1 at 700 K, respectively. At room temperature formyl cyanide does not decompose via unimolecular decomposition because the rate constants of all three paths are minute.