The structure, thermodynamic instability and energetics of NI3, its specific impulse and a strategy for its stabilization

•A theoretical investigation on the causes of NI3 chemical instability is performed.•It is shown that polyvinylchloride resin, polyvinyl acetate resin or polysiloxane resin can stabilize NI3 adduct with ammonia.•By using an empirical equation for NH3.NI3 specific impulse is calculated as 245.5 s. The present work is dedicated to deepen the causes of the physicochemical instability of NI3. As a support study, a theoretical investigation is performed. The quantum chemical calculations were performed by using SE(PM6), HF/6-31G* and DFT/M06-2X/6-311G** approach. The calculated gas phase formation enthalpy to NH3.NI3 is 91.75 kJmol−1. The sublimation enthalpy for the adduct is calculated as 237.75 kJmol−1. By structure calculations, it is shown that the stabilization of NI3 in the NH3.NI3 adduct is consequence of the I-N-I angle increase. The enthalpy for the reaction NH3.NI3 (s) → NH3(g) + NI3 (s) is calculated as 46 kJmol−1. Pure NH3:NI3 detonated only three minutes after dried at room conditions (humidity = 65%, temperature = 39 ºC). On the other hand, the NH3:NI3 polyvinylchloride resin, polyvinyl acetate resin or polysiloxane resin “entrapped” samples, do not detonate after 30 h. By using the empirical equation Is = 17.562 η + 125.551, where Is is the specific impulse (s) and η is the absolute chemical hardness (eV), the specific impulse for NH3.NI3 can be calculated as 185.52 s (HF/6-31G* data) and 163.75 s (DFT/M06-2X/6-311G** data). To NI3the Is calculated values are 201.68s and 168.75 s, respectively. The decrease in the specific impulse values from NI3 to NI3:NH3 is explained as consequence of the increase in the polarizability of the entire system. [Display omitted]