Kinetics and Thermochemistry of Hydroxyacetonitrile (HOCH₂CN) and Its Reaction with Hydroxyl Radical

The potential energy surface for OH + HOCH2CN was investigated computationally with B2PLYP-D3/cc-pVTZ density functional theory for geometries and frequencies, and coupled-cluster theory with double, triple and perturbative quadruple excitations approximately extrapolated to the complete basis set limit for energies. The results were employed with canonical variational transition state (TS) theory and an Eckart tunneling model to obtain rate coefficients, k, for three channels, (1) H abstraction from the C–H bonds, (2) H abstraction from the O–H bond and (3) addition to the nitrile C atom. Over 220–450 K, k1(T) = 2.07 × 10–13 (T/298 K)2.264 exp(+15 K/T) cm3 molecule–1 s–1 and is the dominant pathway, accounting for ca. 85% of total reactivity at 298 K and 1 atm. k2(T) = 5.16 × 10–15 (T/298 K)3.470 exp(+440 K/T) and the high-pressure limit for channel 3, k3,∞(T), was found to be temperature-independent with a value of 2.2 × 10–14 cm3 molecule–1 s–1. Consideration of the low-pressure limit and falloff indicates the high-pressure limit is the relevant quantity for atmospheric conditions. Intramolecular hydrogen bonding both stabilizes the TSs and makes them less flexible. The tropospheric lifetime of HOCH2CN with respect to reaction with OH is estimated to be ∼45 days. Its major degradation product is predicted to be HC(O)CN, with minor contributions from HOC(O)CN and other species. Thermochemistry for HOCH2CN and these two products was obtained.