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.

中文翻译：

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双氰胺钠与硝酸反应性的理论研究

有必要用更安全的推进剂代替目前的肼燃料，基于双氰胺（DCA ^–）的系统已成为有希望的替代品，因为它们与某些氧化剂混合时会自动着火。以前对高声反应机理的研究集中在DCA ^–与氧化剂HNO ₃之间的反应。在这里，我们将DCA ^– + HNO ₃的计算路径与离子对双氰胺钠与硝酸Na [DCA] + HNO ₃的反应坐标进行比较。使用量子力学连续溶剂模型SMD-GIL在气相和溶液中计算焓和自由能。Na [DCA] + HNO ₃的壁垒相对于与裸露阴离子的反应，反应显着降低，并产生放热的出口通道以生成NaNO ₃和反应性中间体HDCA。这些结果表明，Na [DCA]可能会加速点火反应。