Initial Thermal Decomposition Mechanism of (NH(2))(2)C=C(NO(2))(ONO) Revealed by Double-Hybrid Density Functional Calculations

[Image: see text] 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 (NH(2))(2)C=C(NO(2))O and nitric monoxide (NO). The calculated results confirm that an activated barrier is present in the CO–NO bond dissociation process of (NH(2))(2)C=C(NO(2))(ONO). Furthermore, it is proposed that a radical–radical adduct is involved in the exit dissociation path with subsequent dissociation to separate (NH(2))(2)C=C(NO(2))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 (NH(2))(2)C=C(NO(2))(ONO) is obtained by a fitting to the modified Arrhenius form 1.05 × 10(13)(T/300)(0.39) exp[−27.80(T + 205.32)/R(T(2) + 205.32(2))] 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.