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Title: High-pressure stability of 1,1-diamino-2,2-dinitroethene (FOX-7): H/D isotope effect

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USDOE National Nuclear Security Administration (NNSA)
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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Chemical Physics Letters
Additional Journal Information:
Journal Volume: 624; Journal Issue: C; Related Information: CHORUS Timestamp: 2016-12-21 10:40:51; Journal ID: ISSN 0009-2614
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Citation Formats

Tao, Yuchuan, Dreger, Zbigniew A., and Gupta, Yogendra M. High-pressure stability of 1,1-diamino-2,2-dinitroethene (FOX-7): H/D isotope effect. Netherlands: N. p., 2015. Web. doi:10.1016/j.cplett.2015.02.014.
Tao, Yuchuan, Dreger, Zbigniew A., & Gupta, Yogendra M. High-pressure stability of 1,1-diamino-2,2-dinitroethene (FOX-7): H/D isotope effect. Netherlands. doi:10.1016/j.cplett.2015.02.014.
Tao, Yuchuan, Dreger, Zbigniew A., and Gupta, Yogendra M. 2015. "High-pressure stability of 1,1-diamino-2,2-dinitroethene (FOX-7): H/D isotope effect". Netherlands. doi:10.1016/j.cplett.2015.02.014.
title = {High-pressure stability of 1,1-diamino-2,2-dinitroethene (FOX-7): H/D isotope effect},
author = {Tao, Yuchuan and Dreger, Zbigniew A. and Gupta, Yogendra M.},
abstractNote = {},
doi = {10.1016/j.cplett.2015.02.014},
journal = {Chemical Physics Letters},
number = C,
volume = 624,
place = {Netherlands},
year = 2015,
month = 3

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.cplett.2015.02.014

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Cited by: 5works
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  • Understanding the insensitivity/stability of insensitive high explosive crystals requires detailed structural information at high pressures and high temperatures of interest. Synchrotron single crystal x-ray diffraction experiments were used to determine the high-pressure structures of 1,1-diamino-2,2-dinitroethene (FOX-7), a prototypical insensitive high explosive. The phase transition around 4.5 GPa was investigated and the structures were determined at 4.27 GPa (α’-phase) and 5.9 GPa (ε-phase). The α’-phase (monoclinic, P2 1/ n), structurally indistinguishable from the ambient α-phase, transforms to the new ε-phase (triclinic, P1). The most notable features of the ε-phase, compared to the α’-phase, are: formation of planar layers and flattening ofmore » molecules. Density functional theory (DFT-D2) calculations complemented the experimental results. Furthermore, the results presented here are important for understanding the molecular and crystalline attributes governing the high-pressure insensitivity/stability of insensitive high explosive crystals.« less
  • The high pressure-high temperature (HP-HT) phase diagram and decomposition of FOX-7, central to understanding its stability and reactivity, were determined using optical spectroscopy and imaging measurements in hydrostatically compressed and heated single crystals. Boundaries between various FOX-7 phases (α, α’, β, γ, and ε) and melting/decomposition curves were established up to 10 GPa and 750 K. Main findings are: (i) a triple point is observed between α, β, and γ phases ~ 0.6 GPa and ~ 535 K, (ii) previously suggested δ phase is not a new phase but is partly decomposed γ phase, (iii) the α-α’ transition takes placemore » along an isobar, whereas the α’-ε transition pressure decreases with increasing temperature, and (iv) melting/decomposition temperatures increase rapidly with pressure, with an increase in the slope at the onset of the α’-ε transition. Our results differ from the recently reported HP-HT phase diagram for nonhydrostatically compressed polycrystalline FOX-7. In addition, the observed interplay between melting and decomposition suggests the suppression of melting with pressure. Our FTIR measurements at different pressures to 3.5 GPa showed similar decomposition products, suggesting similar decomposition pathways irrespective of the pressure. Lastly, the present results provide new insights into the structural and chemical stability of an important insensitive high explosive (IHE) crystal under well-defined HP-HT conditions.« less
  • Decomposition of the energetic material FOX-7 (1,1-diamino-2,2-dinitroethylene, C{sub 2}H{sub 4}N{sub 4}O{sub 4}) 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 (<35 K) and vibrationally hot (2800 K). The initial decomposition mechanism is explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) level illustrate that conical intersections play an essential role in the decomposition mechanism. Electronically excited S{sub 2} FOX-7 can radiationlessly relax to lower electronic states through (S{sub 2}/S{sub 1}){sub CI} and (S{submore » 1}/S{sub 0}){sub CI} conical intersections and undergo a nitro-nitrite isomerization to generate NO product on the S{sub 0} 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 S{sub 0} state. Ground state FOX-7 decomposition agrees with previous work: the nitro-nitrite isomerization has the lowest average energy barrier, the C–NH{sub 2} 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.« less