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

Shock Tube Investigation of CH₃ + CH₃OCH₃

The title reaction has been investigated in a diaphragmless shock tube by laser schlieren densitometry over the temperature range 1163–1629 K and pressures of 60, 120, and 240 Torr. Methyl radicals were produced by dissociation of 2,3-butanedione in the presence of an excess of dimethyl ether. Rate coefficients for CH₃ + CH₃OCH₃ were obtained from simulations of the experimental data yielding the following expression which is valid over the range 1100–1700 K: <i>k</i> = (10.19 ± 3.0)<i>T</i>^3.78 exp^(−4878/T) cm³ mol^–1s^–1. The experimental results are in good agreement with estimates by Curran and co-workers [Fischer, S. L.; Dryer, F. L.; Curran, H. J. <i>Int. J. Chem. Kinet.</i> <b>2000</b>, <i>32</i> (12), 713–740. Curran, H. J.; Fischer, S. L.; Dryer, F. L. <i>Int. J. Chem. Kinet.</i> <b>2000</b>, <i>32</i> (12), 741–759] but about a factor of 2.6 lower than those of Zhao et al. [Zhao, Z.; Chaos, M.; Kazakov, A.; Dryer, F. L. <i>Int. J. Chem. Kinet.</i> <b>2008</b>, <i>40</i> (1), 1–18]

Shock Tube Investigation of CH₃ + CH₃OCH₃

The title reaction has been investigated in a diaphragmless shock tube by laser schlieren densitometry over the temperature range 1163–1629 K and pressures of 60, 120, and 240 Torr. Methyl radicals were produced by dissociation of 2,3-butanedione in the presence of an excess of dimethyl ether. Rate coefficients for CH₃ + CH₃OCH₃ were obtained from simulations of the experimental data yielding the following expression which is valid over the range 1100–1700 K: <i>k</i> = (10.19 ± 3.0)<i>T</i>^3.78 exp^(−4878/T) cm³ mol^–1s^–1. The experimental results are in good agreement with estimates by Curran and co-workers [Fischer, S. L.; Dryer, F. L.; Curran, H. J. <i>Int. J. Chem. Kinet.</i> <b>2000</b>, <i>32</i> (12), 713–740. Curran, H. J.; Fischer, S. L.; Dryer, F. L. <i>Int. J. Chem. Kinet.</i> <b>2000</b>, <i>32</i> (12), 741–759] but about a factor of 2.6 lower than those of Zhao et al. [Zhao, Z.; Chaos, M.; Kazakov, A.; Dryer, F. L. <i>Int. J. Chem. Kinet.</i> <b>2008</b>, <i>40</i> (1), 1–18]

Shock Tube Investigation of CH₃ + CH₃OCH₃

The title reaction has been investigated in a diaphragmless shock tube by laser schlieren densitometry over the temperature range 1163–1629 K and pressures of 60, 120, and 240 Torr. Methyl radicals were produced by dissociation of 2,3-butanedione in the presence of an excess of dimethyl ether. Rate coefficients for CH₃ + CH₃OCH₃ were obtained from simulations of the experimental data yielding the following expression which is valid over the range 1100–1700 K: <i>k</i> = (10.19 ± 3.0)<i>T</i>^3.78 exp^(−4878/T) cm³ mol^–1s^–1. The experimental results are in good agreement with estimates by Curran and co-workers [Fischer, S. L.; Dryer, F. L.; Curran, H. J. <i>Int. J. Chem. Kinet.</i> <b>2000</b>, <i>32</i> (12), 713–740. Curran, H. J.; Fischer, S. L.; Dryer, F. L. <i>Int. J. Chem. Kinet.</i> <b>2000</b>, <i>32</i> (12), 741–759] but about a factor of 2.6 lower than those of Zhao et al. [Zhao, Z.; Chaos, M.; Kazakov, A.; Dryer, F. L. <i>Int. J. Chem. Kinet.</i> <b>2008</b>, <i>40</i> (1), 1–18]

Theoretical and Experimental Insights into the Dissociation of 2‑Hydroxyethylhydrazinium Nitrate Clusters Formed via Electrospray

Ionic liquids are used for myriad applications, including as catalysts, solvents, and propellants. Specifically, 2-hydroxyethylhydrazinium nitrate (HEHN) has been developed as a chemical propellant for space applications. The gas-phase behavior of HEHN ions and clusters is important in understanding its potential as an electrospray thruster propellant. Here, the unimolecular dissociation pathways of two clusters are experimentally observed, and theoretical modeling of hydrogen bonding and dissociation pathways is used to help rationalize those observations. The cation/deprotonated cation cluster [HEH₂ – H]⁺, which is observed from electrospray ionization, is calculated to be considerably more stable than the complementary cation/protonated anion adduct, [HEH + HNO₃]⁺, which is not observed experimentally. Upon collisional activation, a larger cluster [(HEHN)₂HEH]⁺ undergoes dissociation via loss of nitric acid at lower collision energies, as predicted theoretically. At higher collision energies, additional primary and secondary loss pathways open, including deprotonated cation loss, ion-pair loss, and double-nitric-acid loss. Taken together, these experimental and theoretical results contribute to a foundational understanding of the dissociation of protic ionic liquid clusters in the gas phase