Initial Thermal Decomposition Mechanism of (NH2)2CC(NO2)(ONO) Revealed by Double-Hybrid Density Functional Calculations

This work employs double-hybrid density functionals to re-examine the CO–NO bond dissociation mechanism of nitrite isomer of 1,1-diamino-2,2-dinitro-ethylene (DADNE) into (NH2)2CC­(NO2)O and nitric monoxide (NO). The calculated results confirm that an activated barrier is present in the CO–NO bond dissociation process of (NH2)2CC­(NO2)­(ONO). Furthermore, it is proposed that a radical–radical adduct is involved in the exit dissociation path with subsequent dissociation to separate (NH2)2CC­(NO2)O and NO radicals. The activation and reaction enthalpies at 298.15 K for the nitrite isomer dissociation are predicted to be 43.6 and 5.4 kJ mol–1 at the B2PLYP/6-31G­(d,p) level, respectively. Employing the B2PLYP/6-31G­(d,p) reaction energetics, gradient, Hessian, and geometries, the kinetic model for the CO–NO bond dissociation of (NH2)2CC­(NO2)­(ONO) is obtained by a fitting to the modified Arrhenius form 1.05 × 1013(T/300)0.39 exp­[−27.80­(T + 205.32)/R(T 2 + 205.322)] in units of per second over the temperature range 200–3000 K based on the canonical variational transition-state theory with multidimensional small-curvature tunneling.