Investigation on the Thermal Dissociation of Vinyl Nitrite with a Saddle Point Involved

Hybrid and double-hybrid density functionals are employed to explore the O–NO bond dissociation mechanism of vinyl nitrite (CH₂CHONO) into vinoxy (CH₂CHO) and nitric monoxide (NO). In contrast to previous investigations, which point out that the O–NO bond dissociation of vinyl nitrite is barrierless, our computational results clearly reveal that a kinetic barrier (first-order saddle point) in the O–NO bond dissociation is involved. Furthermore, a radical–radical adduct is recommended to be present on the dissociation path. The activation and reaction enthalpies at 298.15 K for the vinyl nitrite dissociation are calculated to be 91 and 75 kJ mol^–1 at the M062X/MG3S level, respectively, and the calculated reaction enthalpy compares very well with the experimental result of 76.58 kJ mol^–1. The M062X/MG3S reaction energetics, gradient, Hessian, and geometries are used to estimate vinyl nitrite dissociation rates based on the multistructural canonical variational transition-state theory including contributions from hindered rotations and multidimensional small-curvature tunneling at temperatures from 200 to 3000 K, and the rate constant results are fitted to the four-parameter Arrhenius expression of 4.2 × 10⁹ (T/300)^4.3 exp­[−87.5­(T – 32.6)/(T² + 32.6²)] s^–1.