Initial decomposition mechanism for the energy release from electronically excited energetic materials: FOX-7 (1,1-diamino-2,2-dinitroethene, C2H4N4O4)

Abstract

Decomposition of the energetic material FOX-7 (1,1-diamino-2,2-dinitroethylene, C₂H₄N₄O₄) is investigated both theoretically and experimentally. The NO molecule is observed as an initial decomposition product subsequent to electronic excitation. The observed NO product is rotationally cold (2 FOX-7 can radiationlessly relax to lower electronic states through (S₂/S₁)_CI and (S₁/S₀)_CI conical intersections and undergo a nitro-nitrite isomerization to generate NO product on the S₀ state. The theoretically predicted mechanism is consistent with the experimental results. As FOX-7 decomposes on the ground electronic state, thus, the vibrational energy of the NO product from FOX-7 is high. The observed rotational energy distribution for NO is consistent with the final transition state structure on the S₀ state. Ground state FOX-7 decomposition agrees with previous work: the nitro-nitrite isomerization has the lowest average energy barrier, the C–NH₂ bond cleavage is unlikely under the given excitation conditions, and HONO formation on the ground state surface is energy accessible but not the main process.