Theoretical Investigation of the Reactivity of Sodium Dicyanamide with Nitric Acid

There is a need to replace current hydrazine fuels with safer propellants, and dicyanamide (DCA^-)-based systems have emerged as promising alternatives because they autoignite when mixed with some oxidizers. Previous studies of the hypergolic reaction mechanism have focused on the reaction between DCA^- and the oxidizer HNO₃; here, we compare the calculated pathway of DCA^- + HNO₃ with the reaction coordinate of the ion pair sodium dicyanamide with nitric acid, Na[DCA] + HNO₃. Enthalpies and free energies are calculated in the gas phase and in solution using a quantum mechanical continuum solvation model, SMD-GIL. The barriers to the Na[DCA] + HNO₃ reaction are dramatically lowered relative to those of the reaction with the bare anion, and an exothermic exit channel to produce NaNO₃ and the reactive intermediate HDCA appears. These results suggest that Na[DCA] may accelerate the ignition reaction.