Effect of electric fields on the reaction rates in shock initiating and detonating solid explosives

2014

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 (<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 S2 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.

Section: Introductionmentioning

confidence: 99%

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

Yuan

2014

“…3,18 Electronic excitation of condensed phase energetic species has been suggested and recognized as a major factor in the release of stored energy from energetic molecules over the past 50 years. [1][2][3][4][5][6][18][19][20][21][22][23] In this instance, conical intersections between different potential energy surfaces play a key role in the ultrafast (∼100 fs) decomposition mechanisms. 5,6,24 In nonadiabatic unimolecular chemistry, a conical intersection is the crossing (interaction) point between two electronic states or two potential energy surfaces: conical intersections are widely employed to explain and understand the excited state chemistry of organic and inorganic molecules.…”

Section: Introductionmentioning

confidence: 99%

Azole energetic materials: Initial mechanisms for the energy release from electronical excited nitropyrazoles

Yuan

2014

Decomposition of energetic material 3,4-dinitropyrazole (DNP) and two model molecules 4-nitropyrazole and 1-nitropyrazole is investigated both theoretically and experimentally. The initial decomposition mechanisms for these three nitropyrazoles are explored with complete active space self-consistent field (CASSCF) level. The NO molecule is observed as an initial decomposition product from all three materials subsequent to UV excitation. Observed NO products are rotationally cold (<50 K) for all three systems. The vibrational temperature of the NO product from DNP is (3850 ± 50) K, 1350 K hotter than that of the two model species. Potential energy surface calculations at the CASSCF(12,8)/6-31+G(d) level illustrate that conical intersections plays an essential role in the decomposition mechanism. Electronically excited S2 nitropyraozles can nonradiatively relax to lower electronic states through (S2/S1)CI and (S1/S0)CI conical intersection and undergo a nitro-nitrite isomerization to generate NO product either in the S1 state or S0 state. In model systems, NO is generated in the S1 state, while in the energetic material DNP, NO is produced on the ground state surface, as the S1 decomposition pathway is energetically unavailable. The theoretically predicted mechanism is consistent with the experimental results, as DNP decomposes in a lower electronic state than do the model systems and thus the vibrational energy in the NO product from DNP should be hotter than from the model systems. The observed rotational energy distributions for NO are consistent with the final structures of the respective transition states for each molecule.

“…Recall that the electrical potential between crystal planes is ∼10 8 V/cm and, as the crystal fractures, this energy can easily remove electrons from molecules in the crystal, especially at defect and inclusion sites. [26][27][28][29] Electrons can be very reactive in initiating chemical decomposition. Shock and compression waves can also generate excited electronic states by excitonic and by HOMO/LUMO gap modulation molecular mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Experimental and theoretical studies of the decomposition of new imidazole based energetic materials: Model systems

2012

Decomposition of three imidazole based model energetic systems (2-nitroimidazole, 4-nitroimidazole, and 1-methyl-5-nitroimidazole) is investigated both experimentally and theoretically. The initial decomposition mechanism for these three nitroimidazoles is explored with nanosecond energy resolved spectroscopy, and quantum chemical theory at the complete active space self-consistent field (CASSCF) level. The NO molecule is observed as an initial decomposition product from these three nitroimidazoles subsequent to UV excitation. A unique, excitation wavelength independent dissociation channel is observed for these three nitroimidazoles that generates the NO product with a rotationally cold (∼50 K) and a vibrationally mildly hot (∼800 K) distribution. Potential energy surface calculations at the CASSCF∕6-31G(d) level of theory illustrate that conical intersections play an important and essential role in the decomposition mechanism. Electronically excited S(2) nitroimidazole molecules relax to the S(1) state through the (S(2)∕S(1))(CI) conical intersection, and undergo a nitro-nitrite isomerization to generate the NO product from the S(1) potential energy surface. Nevertheless, NO(2) elimination and nitro-nitrite isomerization are expected to be competitive reaction mechanisms for the decomposition of these molecules on the ground state potential energy surface from the Franck-Condon equilibrium geometry through thermal dissociation.