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A combined theoretical and experimental study is performed for the initiation of chemistry process in high explosive crystals from a solid-state physics viewpoint. In particular, we were looking for the relationship between the defect-induced deformation of the electronic structure of solids, electronic excitations, and chemical reactions under sho...
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... any rate, a part of the glow preceding the appearance of the acoustic signal Fig. 5 is undoubtedly related to the vir- gin sample. It can be identified as pre-explosion luminescence, 77 which is of the most interest for us. The short wavelength edge of the luminescence Fig. 7 is in optical transparent range for all objects under investigation. This allows us to rule out a photomultiplication process 84 as a probable mechanism of hole ...
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... 1,4-dinitroimidazole ABT 1,1 0 -azobistetrazole AGTZ aminoguanidinium-1H-tetrazolate ATZ 5-amino-1H-tetrazole bicyclo-HMX 1,3,4,6-tetranitrooctahydroimidazo- [4,5- 1,3,5-trinitro-1,3,5-triazinane TATB 1,3,5-triamino-2,4,6-trinitrobenzene TEX diazatetracyclo[5.5.0.0 5,9 .0 3,11 ]-dodecane TKX-50 dihydroxylammonium 5,5 0 -bistetrazole-1,1 0 -diolate TNAZ 1,3,3-trinitroazetidine TNB 1,3,5-trinitrobenzene TNE tetranitratoethane TNT 2,4,6-trinitrotoluene 1 Definition of the problem Impact sensitivity (IS) is a complex phenomenon, which cannot be defined analytically due to its stochastic nature. The known unit of IS is h 50 , which determines a minimum height needed to initiate explosion of 50% of samples. ...
... In the second case, thermally and mechanically induced electron transfer (ET) can take place that leads to the involvement of ExSs. Ab initio calculations showed that compression of a crystal to at least 30 GPa causes an electronic excitation (EE) equivalent to 2-5 eV [11]. A principal scheme of these two processes is presented in Fig. 9.1. ...
This chapter concerns with response of solid-state properties of energetic materials to the applied mechanical energy (ME) as an initiation factor of impact sensitivity (IS). Particularly, the processes of mechanically and thermally induced electron transfer (ET) as well as phonon-to-valence vibration energy transfer are in the focus of this review. Thus, a number of crystal properties, like band gap compressibility, crystal morphology, bulk modulus, phonons, and other are discussed in terms of IS phenomenon. Described models of IS are applied for aromatic, aliphatic, and heterocyclic nitro and nitrato compounds, metal azides, bistetrazole-based and aryl diazonium energetic salts (ESs). Finally, an attempt is made to compare applicability of features of isolated molecules with properties of its crystalline phases and to highlight their advantages and drawbacks.
... Energetic Materials (EMs) store a large amount of chemical energy that can be converted to mechanical energy by molecular decomposition for industrial and military applications [1] . Excited electronic states of EMs are proven to play a crucial role in molecular decomposition, which can be generated by different ignition processes such as shocks, sparks, and heat [2][3][4][5][6][7][8] . Theoretical calculations show that compression at a pressure of greater than 30 GPa can induce electronic transition equal to 2-2.5 eV, which is comparable to the low lying excited states of the EMs [6] . ...
... Excited electronic states of EMs are proven to play a crucial role in molecular decomposition, which can be generated by different ignition processes such as shocks, sparks, and heat [2][3][4][5][6][7][8] . Theoretical calculations show that compression at a pressure of greater than 30 GPa can induce electronic transition equal to 2-2.5 eV, which is comparable to the low lying excited states of the EMs [6] . The velocity of the detonation wave in an explosive is about 10 km/s. ...
Excited-state dynamics of two novel energetic nitrogen-rich aryl-tetrazole molecules were investigated using femtosecond transient absorption spectroscopy. The internal conversion from Sn to S1 occurred in the 0.3-0.5 ps; vibrational relaxation within S1 states transpired in a 1.8-5 ps time scale and, subsequently, the intersystem crossing was observed with lifetimes of 7.8 ps and 129 ps. The nitro-substituted tetrazole demonstrated a faster decay with a weaker fluorescence compared to the amino-substituted derivative. We believe that the high nitrogen content in the former resulted in a possible more rapid nonradiative decay.
... Energetic materials (EMs) store enormous energy in the chemical form that can be easily converted to kinetic energy by molecular decomposition and retrieved energy can be used in industrial and military applications [5]. Excited-state dynamics of the energetic materials provide an insight into the molecular decomposition mechanisms for different ignition processes, such as heat, shock and compression waves etc. [5,6]. The compression of the material at a pressure of 30 GPa or above could induce an electronic excitation nearly equal to the lowest singlet excited states of EMs [6,7]. ...
... Excited-state dynamics of the energetic materials provide an insight into the molecular decomposition mechanisms for different ignition processes, such as heat, shock and compression waves etc. [5,6]. The compression of the material at a pressure of 30 GPa or above could induce an electronic excitation nearly equal to the lowest singlet excited states of EMs [6,7]. The investigation of the electronic, chemical and structural changes of the excited states of EMs enables us to understand the behaviour of EMs at the molecular level. ...
We report the time and frequency-resolved coherent anti-Stokes Raman spectroscopy (CARS) data of nitro-substituted tetrazole-N-(hetero)aryl derivatives with ∼50 femtosecond pulses. CARS experiments were performed to comprehend the intramolecular vibrational redistribution (IVR) dynamics through vibrational couplings in Amino (6) and Nitro (8) substituted tetrazoles. The present study elevates the applications of tetrazoles derivatives since their energetic properties are comparable with the secondary explosives RDX/TNT. The Fourier transforms of the CARS transients revealed the possible IVR mechanisms in tetrazole-N-(hetero)aryl derivatives. Further, the average coherent vibrational decay time (T2) were estimated to be in the range of ∼120-200 fs from the CARS transients.
... In the laboratory, these excited states are readily accessible once the sample is exposed to ultraviolet (UV) photons. 5,45 However, only a few studies have been pursued to unravel the fragmentation processes of RDX that occur after electronic excitation (Table S1). 4,16,23,[25][26]28 Here, the majority of the UV photolysis experiments are conducted in the gas phase by Bernstein and co-workers. ...
... TPD profiles of the ion counts recorded at mass-to-charge ratio of30,31,42,44,45,46,58,59,60,71,72,73,74,75,81, 87, 88, 89, 97, 98, 99, 101, 105, 117, 118, 119, 128, 146, 149 and 191 at a photoionization energy of 10.49 eV, after exposure to 254 nm at doses of 10.7 ± 1.0, 0.5 ± 0.1 and 0.10 ± 0.02 eV molecule -1 . study, the photoionization energy of 10.49 eV is lower than the ionization energy of formaldehyde (H2CO, IE = 10.88 eV); therefore, the signal at m/z = 30 has to be assigned to nitrogen monoxide (NO; IE = 9.26 eV). ...
Energetic materials such as 1,3,5-trinitro-1,3,5-triazinane (RDX) are known to photodissociate when exposed to UV light. However, the fundamental photochemical process(es) that initiate the decomposition of RDX is (are) still debatable. In this study we investigate the photodissociation of solid-phase RDX at four distinct UV wavelengths (254 nm (4.88 eV), 236 nm (5.25 eV), 222 nm (5.58 eV), 206 nm (6.02 eV)) exploiting a surface science machine at 5 K. We also conducted dose-dependent studies at the highest and lowest photon energy of 206 nm (6.02 eV) and 254 nm (4.88 eV). The products were monitored online and in situ via infrared spectroscopy. During the temperature programmed desorption phase, the subliming products were detected with a reflectron time-of-flight mass spectrometer coupled with soft-photoionization at 10.49 eV (PI-ReTOF-MS). Infrared spectroscopy revealed the formation of small molecules including nitrogen monoxide (NO), nitrogen monoxide dimer ([NO]2), dinitrogen trioxide (N2O3), carbon dioxide (CO2), carbon monoxide (CO), dinitrogen monoxide (N2O), water (H2O) and nitrite group (-ONO) while ReTOF-MS identified 32 cyclic and acyclic products. Among these, 11 products such as nitryl isocyanate (CN2O3), 5-nitro-1,3,5-triazinan-2-one (C2H6N4O3) and 1,5-dinitro-1,3,5-triazinan-2-one (C3H5N5O5) were detected for the first time in photodecomposition of RDX. Dose-dependent in combination with wavelength-dependent photolysis experiments aid to identify key primary and secondary products as well as distinguished pathways that are more preferred at lower and higher photon energies. Our experiments reveled that N-NO2 bond fission and nitro-nitrite isomerization are the initial steps in the UV photolysis of RDX. Reaction mechanisms are derived by comparing the experimental findings with previous electronic structure calculations to rationalize the origin of the observed products. The present study can assist in understanding the complex chemistry behind the photodissociation of electronically excited RDX molecule, thus bringing us closer to unravel the decomposition mechanisms of nitramine-based explosives.
... Early experiments [78,79] demonstrated that the defects in energetic materials could obviously influence the detonation. A large series of theoretical investigations further verified the effects of defects on the detonation properties [13,75,[80][81][82][83][84][85][86], including vacancy dimmers, molecular vacancies, edge dislocations. For example, the fast chemical reactions associated with the interactions between impact waves and density discontinuities were linked with different binding energies and different mutual orientations of vacancy dimmers [75]; the lattice defects promoting HOMO-LUMO transitions caused the N-NO 2 bond breaking and the favorable environment for initiation in RDX [80]; Pan et al. [22] investigated the donation performances, thermal properties, and impact sensitivity by replacing the N-NO 2 groups with the introduced oxygen atoms into the azaisowurtzitane cage, and found that the impact sensitivity was obviously decreased after subsitution; decreased band gap was ascribed to the combination of the defect and the uniaxial strain [86]; the molecular dynamics simulations suggested that the larger the void was, the greater the sensitivity of HMX [87]. ...
In this study, the doped defects in nitromethane crystals were investigated using first-principles calculations for the first time. We introduce dopant atoms in the interstitial sites of the nitromethane lattice, aiming to study the effects of element-doping on the structural properties, electronic properties, and sensitivity characteristics. The obtained results show that doped defects obviously affect the neighboring nitromethane molecules. The modification of electronic properties shows that the band gaps are significantly influenced by doped defects. Partial density of states and population analysis further reveal the mechanism for sensitivity control of nitromethane. It is shown that the new electronic states were introduced in the forbidden bands and the doped defects resulted in charge redistributions in the systems.
The valence and conduction band edge positions as well as defect levels of pure and X-doped NM
... Energetic materials (EMs) are organic compounds containing nitro, azide and hydrazino groups. Interestingly, they encompass large amount of chemical energy, which can be released upon decomposition/detonation under typical initiation events, such as shocks, arcs, sparks, heat, pressure waves, and laser pulses [1][2][3][4]. They have been widely exploited as explosives, rocket propellants, fuels and pyrotechniques. ...
... About a decade ago, Bernstein, for the first time, argued that these electronic excitations due to pressure or shock waves are a fact and cannot be ignored in the investigation of the decomposition process of any energetic material. 10,11 Therefore, exploring chemical dynamics of energetic molecules following electronic excitation is an important pursuit to understand the explosive property of energetic molecules from a fundamental point of view. ...
... Furthermore, several time-independent SA-CASSCF calculations are performed to explore electronic excitation energies and characters of DMNA and DMNA-Fe using both (14,11) and (8,5) active spaces with the 6-31G(d) basis set executing Gaussian 09. 34 Minimum energy conical intersections (MECIs) have been identified using the algorithm implemented in G09 35 at both the SA-CASSCF (14,11) and the SA-CASSCF(8,5) levels of theory. ...
... Furthermore, several time-independent SA-CASSCF calculations are performed to explore electronic excitation energies and characters of DMNA and DMNA-Fe using both (14,11) and (8,5) active spaces with the 6-31G(d) basis set executing Gaussian 09. 34 Minimum energy conical intersections (MECIs) have been identified using the algorithm implemented in G09 35 at both the SA-CASSCF (14,11) and the SA-CASSCF(8,5) levels of theory. The (14,11) active space for DMNA and DMNA-Fe is given in S1 of the supplementary material for reader's perusal. ...
Conical intersections are now firmly established to be the key features in the excited electronic state processes of polyatomic energetic molecules. In the present work, we have explored conical intersection-mediated nonadiabatic chemical dynamics of a simple analogue nitramine molecule, dimethylnitramine (DMNA, containing one N–NO2 energetic group), and its complex with an iron atom (DMNA-Fe). For this task, we have used the ab initio multiple spawning (AIMS) dynamics simulation at the state averaged-complete active space self-consistent field(8,5)/6-31G(d) level of theory. We have found that DMNA relaxes back to the ground (S0) state following electronic excitation to the S1 excited state [which is an (n,π*) excited state] with a time constant of approximately 40 fs. This AIMS result is in very good agreement with the previous surface hopping-result and femtosecond laser spectroscopy result. DMNA does not dissociate during this fast internal conversion from the S1 to the S0 state. DMNA-Fe also undergoes extremely fast relaxation from the upper S1 state to the S0 state; however, this relaxation pathway is dissociative in nature. DMNA-Fe undergoes initial Fe–O, N–O, and N–N bond dissociations during relaxation from the upper S1 state to the ground S0 state through the respective conical intersection. The AIMS simulation reveals the branching ratio of these three channels as N–N:Fe–O:N–O = 6:3:1 (based on 100 independent simulations). Furthermore, the AIMS simulation reveals that the Fe–O bond dissociation channel exhibits the fastest (time constant 24 fs) relaxation, while the N–N bond dissociation pathway features the slowest (time constant 128 fs) relaxation. An intermediate time constant (30 fs) is found for the N–O bond dissociation channel. This is the first nonadiabatic chemical dynamics study of metal-contained energetic molecules through conical intersections.
... In the past decades, research on laser initiation of energetic materials has been carried out world widely, including experimental (Ahmad et al., 2009;Aluker et al., 2010;Damm & Maiorov, 2010;Abdulazeem et al., 2011;Zhang et al., 2014Zhang et al., , 2015 and theoretical studies (Babushok et al., 2007;Cohen et al., 2007;Lee et al., 2008;Civiš et al., 2011;Aluker et al., 2012). Up to present, there were two explanations for the mechanism of laser initiation: Thermochemical mechanism (Bourne, 2001;Shui et al., 2013), and photochemical mechanism (Kuklja et al., 2001;Kuklja, 2003;Bhattacharya et al., 2010Bhattacharya et al., , 2012Aluker et al., 2011). ...
An experimental investigation into laser ablation of secondary explosives, cyclotetramethylene tetranitramine (HMX), has been carried out by using a solid-state laser at the wavelength of 1064 nm. The ion particles of decomposition were detected by using a time-of-flight mass spectrometer. Possible attributions of both negative ions and positive ions were obtained. Some obvious peaks were found at m/z = 18, 28, 46, 60, and 106, corresponding to H 2 O, CO/N 2 /H 2 CN, NO 2 , CH 2 NO 2 /N 2 O 2 , and N(NO 2 ) 2 /CH 2 (NO 2 ) 2 , respectively. According to the distribution of the particles, three possible pathways were proposed to explain the process of particles. The results may shed some light on the possible decomposition mechanism of HMX under laser initiation.
... Theoretical work on quantum-mechanical processes involved in shock-induced reactions has primarily been focused along two directions: thermal reactions produced by shock heating [2][3][4], and prompt reactions caused by shock-induced electronic excitations [6][7][8][9][10][11]. Previous work on thermal reactions is primarily focused on the effects of weak shock waves near or below the threshold required to produce observable reaction [2,3]. ...
... Electronically-induced reactions have been predicted by Gilman [6], Kuklja, Stefanovich and Kunz [7], and Kuklja et al. [8,9]. A framework has been developed that predicts large changes in the electronic structure of molecules and the lattice in response to compression and strain. ...
... The vibrational structure of molecules and anharmonic couplings between modes dictate rates of vibrational energy transfer as shown by Dlott and Fayer [2] and Tokmakoff, Dlott, and Fayer [3]. The electronic structure of molecules, which depends strongly on the functionality of the molecule and its geometry, determine the electronic band structure of the solid, which is key to the electronically-induced reaction mechanism of Kuklja et al. [7][8][9]. At the crystal lattice level, the geometric arrangement of the molecules in the lattice is key to all known and proposed reaction mechanisms -the relative geometry of molecules affects vibrational coupling in the solid, affects the electronic band structure, and influences relative motion of defects and collisions between molecules as Dick et al. [21] describe. ...
Understanding the mechanisms by which shock waves initiate chemical reactions in explosives is key to understanding their unique and defining property: the ability to undergo rapid explosive decomposition in response to mechanical stimulus. Although shock-induced reactions in explosives have been studied experimentally and computationally for decades, the nature of even the first chemical reactions that occur in response to shock remain elusive. To predictively understand how explosives respond to shock, the detailed sequence of events that occurs – mechanical deformation, energy transfer,bond breakage, and first chemical reactions – must be understood at the quantum-mechanical level. This paper reviews recent work in this field and ongoing experimental and theoretical work at Sandia National Laboratories in this important area of explosive science.
... Nonadiabatic interactions through conical intersections between zero order adiabatic electronic states play a key role in the ultrafast (<100 fs) decomposition pathways proffered. [27][28][29][30][31][32] Determination of decomposition reaction kinetics, dynamics, and mechanisms for these large energetic molecules energized to excited electronic states (by shocks, arcs, sparks, light, . . .) emphasizes the importance of fundamental chemical physics to the technological advance of newly synthesized molecular energy storage systems, energetic materials, and fuels. ...
Unimolecular decomposition of energetic molecules, 3,3′-diamino-4,4′-bisfuroxan (labeled as A) and 4,4′-diamino-3,3′-bisfuroxan (labeled as B), has been explored via 226/236 nm single photon laser excitation/decomposition. These two energetic molecules, subsequent to UV excitation, create NO as an initial decomposition product at the nanosecond excitation energies (5.0-5.5 eV) with warm vibrational temperature (1170 ± 50 K for A, 1400 ± 50 K for B) and cold rotational temperature (<55 K). Initial decomposition mechanisms for these two electronically excited, isolated molecules are explored at the complete active space self-consistent field (CASSCF(12,12)/6-31G(d)) level with and without MP2 correction. Potential energy surface calculations illustrate that conical intersections play an essential role in the calculated decomposition mechanisms. Based on experimental observations and theoretical calculations, NO product is released through opening of the furoxan ring: ring opening can occur either on the S1 excited or S0 ground electronic state. The reaction path with the lowest energetic barrier is that for which the furoxan ring opens on the S1 state via the breaking of the N1 - O1 bond. Subsequently, the molecule moves to the ground S0 state through related ring-opening conical intersections, and an NO product is formed on the ground state surface with little rotational excitation at the last NO dissociation step. For the ground state ring opening decomposition mechanism, the N - O bond and C - N bond break together in order to generate dissociated NO. With the MP2 correction for the CASSCF(12,12) surface, the potential energies of molecules with dissociated NO product are in the range from 2.04 to 3.14 eV, close to the theoretical result for the density functional theory (B3LYP) and MP2 methods. The CASMP2(12,12) corrected approach is essential in order to obtain a reasonable potential energy surface that corresponds to the observed decomposition behavior of these molecules. Apparently, highly excited states are essential for an accurate representation of the kinetics and dynamics of excited state decomposition of both of these bisfuroxan energetic molecules. The experimental vibrational temperatures of NO products of A and B are about 800-1000 K lower than previously studied energetic molecules with NO as a decomposition product.
