FOX-7 is a high energetic material with low sensitivity, and it has been attracted to science since it was first synthesized in 1998. Understanding the reaction mechanisms involved in the initial decomposition and successive reactions of this energetic material is important to predict the performance, stability, and sensitivity. A sample of crystal α-FOX-7 was photolytically triggering the decomposition by pumping energy into these molecules via single wavelength ultraviolet photodissociation (UVPD) in discrete experiments at 532 and 355 nm (225 and 337 kJ mol−1). Oxygen (O2) was detected at both experiments; nitric oxide (NO) was only detected at the higher energy experiment (355 nm); amino radical (NH2) and nitrogen dioxide (NO2) was not detected at any experiment. Our multi-reference calculations (CASPT2/CASSCF) confirm that the O2 formation involves intersystem crossing (ISC). In addition, since the gas phase potential energy calculations cannot explain the absence of NO or NO2 decomposition at lower energy experiment (532 nm), we explore ab initio density functional theory (DFT) calculations to simulate the actual solid phase environment which turns out the relevant barriers of NH2, NO and NO2 decomposition significantly increase due to intermolecular hydrogen bond bonding. Our combination of UVPD experimental findings and electronic structure calculations reveal that the significance of ISC of newly found O2 decomposition pathway and the non-negligible intermolecular interactions of NH2, NO and NO2 decomposition.

Ab initio study on the decomposition of solid 1,1-diamino-2,2-dinitroethylene (FOX-7)

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ACS Fall 2022

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