Mechanism of Thermal Unimolecular Decomposition of TNT (2,4,6-Trinitrotoluene): A DFT Study

Characterization of industrial TNT in ammunition shells: An in-depth study of artificial aging effects using Fourier-Transform infrared spectroscopy and gas chromatography-mass spectrometry

In this study, we comprehensively investigated the degradation of industrial trinitrotoluene (TNT), focusing on the effects of aging and direct contact with steel surfaces, mirroring real-world usage conditions. While practical knowledge exists regarding this degradation, the existing literature lacks in-depth insights into the underlying processes. To address this gap, we conducted experiments using small steel samples, representative of military ammunition casings, which were coated with TNT and subjected to 30 days of heating at 75 °C under vacuum conditions. A subset of these samples was coated with a protective red alkyd paint. After the aging process, the TNT was carefully removed from the metal surfaces and subjected to a comprehensive analysis encompassing scanning electron microscopy, Fourier-transform infrared spectroscopy, and gas chromatography-mass spectrometry. Our results reveal a remarkable preservation of the chemical integrity of industrial TNT, even in the presence of thermal stress and direct steel contact. Although superficial changes were observed in the TNT's appearance, all analytical data consistently demonstrated the maintenance of its chemical composition. Notably, the sole change in composition was attributed to the presence of degradation products associated with the alkyd paint coating, rather than intrinsic TNT degradation. These findings underscore the negligible impact of degradation processes on TNT in scenarios involving the solid-phase thermal stress of TNT in direct contact with metal, significantly enhancing our understanding of TNT safety when packaged within steel artifacts-a common context in military ammunition.

Exploring the thermal decomposition and detonation mechanisms of 2,4-dinitroanisole by TG-FTIR-MS and molecular simulations

2,4-dinitroanisole (DNAN), an insensitive explosive, has replaced trinitrotoluene (TNT) in many melt-cast explosives to improve the safety of ammunition and becomes a promising material to desensitize novel explosives of high sensitivity. Here, we combine thermogravimetric-Fourier transform infrared spectrometry-Mass spectrometry (TG-FTIR-MS), density functional theory (DFT), and ReaxFF molecular dynamics (MD) to investigate its thermal decomposition and detonation mechanisms. As revealed by TG-FTIR-MS, the thermal decomposition of DNAN starts at ca. 453 K when highly active NO2 is produced and quickly converted to NO resulting in the formation of a large amount of Ph(OH)(OH2)OCH3+. DFT calculations show that the activation energy of DNAN is higher than that of TNT due to the lack of α-H. Further steps in both thermal decomposition and detonation reactions of the DNAN are dominated by bimolecular O-transfers. ReaxFF MD indicates that DNAN has a lower heat of explosion than TNT, in accordance with the observation that the activation energies of polynitroaromatic explosives are inversely proportional to their heat of explosion. The inactive -OCH3 group and less nitro groups also render DNAN higher thermal stability than TNT.

Unimolecular dissociation of C6H6-C6H5Cl, C6H6-C6H3Cl3, and C6H6-C6Cl6 complexes using machine learning approach

The application of Machine Learning (ML) algorithms in chemical sciences, particularly computational chemistry, is a vastly emerging area of modern research. While many applications of ML techniques have already been in place to use ML based potential energies in various dynamical simulation studies, specific applications are also being successfully tested. In this work, the ML algorithms are tested to calculate the unimolecular dissociation time of benzene-hexachlorobenzene, benzene-trichlorobenzene, and benzene-monochlorobenzene complexes. Three ML algorithms, namely, Decision-Tree-Regression (DTR), Multi-Layer Perceptron, and Support Vector Regression are considered. The algorithms are trained with simulated dissociation times as functions (attributes) of complexes' intramolecular and intermolecular vibrational energies. The simulation data are used for an excitation temperature of 1500 K. Considering that the converged result is obtained with 1500 trajectories, an ML algorithm trained with 700 simulation points provides the same dissociation rate constant within statistical uncertainty as obtained from the converged 1500 trajectory result. The DTR algorithm is also used to predict 1000 K simulation results using 1500 K simulation data.

Effects of oxidizing molecules on the thermal decomposition of TTDO by ab initio molecular dynamics simulations

Oxidizing molecules play a very important role in improving the comprehensive properties of energetic materials. Recently, a series of energetic cocrystals containing 2,4,6-triamino-1,3,5-triazine-1,3-dioxide (TTDO) and oxidizing molecule have been successfully prepared. Therefore, ab initio molecular dynamics were used to simulate the thermal decomposition process of TTDO, TTDO:H₂O₂, TTDO:HNO₃, and TTDO:HClO₄ crystals at 3000 K to study the role of oxidizing molecules during the thermal decomposition of TTDO. The initial decomposition paths of the TTDO crystal include N-H bond breaking, C-N bond breaking, and intramolecular and intermolecular H transfers. The formation mechanisms of H₂O, N₂, and CO₂ in the four crystals are completely different. The key formation mechanism of H₂O is the combination of O with OH, that of N₂ is the formation of the -N-N- structure, and that of CO₂ is to form the intermediate CO-R with carbonyl structure that form the fragment with the -O-C-O- structure. All the oxidizers H₂O₂, HNO₃, and HClO₄ involve in the formation of H₂O, N₂, and CO₂. The formation mechanisms of urea during the decomposition process of the four crystals are completely different, but the key step is to produce the structure of -N-CO-N-. An analysis of N_x shows that H₂O₂, HNO₃ and HClO₄ affect not only the types of N_x, but also its formation mechanisms. Among them, HNO₃ has the greatest influence on N_x.

Search for the Decomposition Process of 2,4,6-Trinitrotoluene by an Evolutionary Algorithm

In this paper, we explored stable states in the system of 2,4,6-trinitrotoluene (TNT) crystal with a few additional hydrogen radicals (H_add's) using a structure-search scheme based on first-principles calculations and an evolutionary algorithm (EA) to get insights into the decomposition process of TNT. We introduced three evolutionary operators acting on H_add's and transforming only local structures of TNT molecules: "displacement", "permutation", and "mating". We searched for stable structures by increasing the number of H_add's (n) from 1 to 2, 3, 4, 6, and 8 and constructed a convex-hull diagram for the formation energy from solid TNT and solid hydrogen. We showed that the system of n = 6 had the largest energy reduction, in which five of the eight TNT molecules in the calculation cell were transformed into NO, H₂O, C₂H₃N, C₂NO₃H₃, C₈N₂O₄H₇, C₉N₂O₈H₅, and C₁₄N₇O₁₂H₁₁. Analysis of the structural transformations observed during the EA search indicates that (1) the H_add's approaching the TNT molecules react with C, forming a six-membered ring, and with N and O in nitro groups, leaving the TNT molecules as NO, H₂O, C₂H₃N, and C₂NO₃H₃, and (2) the partially decomposed TNT molecules are bonded to one another via C, N, and O.

Unimolecular Decomposition Reactions of Picric Acid and Its Methylated Derivatives─A DFT Study

To handle energetic materials safely, it is important to have knowledge about their sensitivity. Density functional theory (DFT) has proven a valuable tool in the study of energetic materials, and in the current work, DFT is employed to study the thermal unimolecular decomposition of 2,4,6-trinitrophenol (picric acid, PA), 3-methyl-2,4,6-trinitrophenol (methyl picric acid, mPA), and 3,5-dimethyl-2,4,6-trinitrophenol (dimethyl picric acid, dmPA). These compounds have similar molecular structures, but according to the literature, mPA is far less sensitive to impact than the other two compounds. Three pathways believed important for the initiation reactions are investigated at 0 and 298.15 K. We compare the computed energetics of the reaction pathways with the objective of rationalizing the unexpected sensitivity behavior. Our results reveal a few if any significant differences in the energetics of the three molecules, and thus do not reflect the sensitivity deviations observed in experiments. These findings point toward the potential importance of crystal structure, crystal morphology, bimolecular reactions, or combinations thereof on the impact sensitivity of nitroaromatics.

Early thermal decay of energetic hydrogen- and nitro-free furoxan compounds: the case of DNTF and BTF

Exploration of the initial reactions of H-free and nitro-free energetic materials could enrich our understanding of the thermal decomposition mechanism of various energetic materials (EMs). In this work, two furoxan compounds, 3,4-dinitrofurazanfuroxan (DNTF) and benzotrifuroxan (BTF), were investigated to shed light on the decay mechanism of furoxan compounds based on the combination of self-consistent charge density functional tight binding and molecular dynamics simulations. The results show that DNTF and BTF decay via a unimolecular mechanism, and the transformation of the furoxan ring into a nitro group is suggested as a novel initial channel. Five initial steps of DNTF thermal decomposition are observed, including NO₂ loss and the N(O)-O bond cleavage of the central and peripheral rings. The bond cleavage of peripheral rings dominates the decay at low temperatures, while the central ring opening and C-NO₂ dissociation govern the high temperature decay. Besides, NO₂, CO and NO fragments are mainly yielded at high temperatures, while CO₃N₂ is dominant at low temperatures. The three-stage characteristic of the exothermic BTF decay is described under programmed heating conditions for the first time. Four initial steps of BTF thermal decomposition were identified, including furoxan ring opening reactions and the breakage of the 6-membered ring C-C bond. The cleavage of the N(O)-O bond is dominant in the initial step of BTF decomposition under different heating conditions, and the frequency increases with increasing temperature. In addition, the amounts of CON, ON and CO are higher at high temperatures, while C₂O₂N₂ shows an opposite trend. The findings of this work provide deep insights into the complicated sensitivity mechanism of EMs.

Recruiting Perovskites to Degrade Toxic Trinitrotoluene

Everybody knows TNT, the most widely used explosive material and a universal measure of the destructiveness of explosions. A long history of use and extensive manufacture of toxic TNT leads to the accumulation of these materials in soil and groundwater, which is a significant concern for environmental safety and sustainability. Reliable and cost-efficient technologies for removing or detoxifying TNT from the environment are lacking. Despite the extreme urgency, this remains an outstanding challenge that often goes unnoticed. We report here that highly controlled energy release from explosive molecules can be accomplished rather easily by preparing TNT-perovskite mixtures with a tailored perovskite surface morphology at ambient conditions. These results offer new insight into understanding the sensitivity of high explosives to detonation initiation and enable many novel applications, such as new concepts in harvesting and converting chemical energy, the design of new, improved energetics with tunable characteristics, the development of powerful fuels and miniaturized detonators, and new ways for eliminating toxins from land and water.

Thermal Decomposition of Gas-Phase Bis(1,2,4-oxadiazole)bis(methylene) Dinitrate (BODN): A CCSD(T)-F12/DFT-Based Study of Reaction Pathways

Electronic structure methods based on density functional theory and coupled-cluster theory were employed to characterize elementary steps for the gas-phase thermal decomposition of bis(1,2,4-oxadiazole)bis(methylene) dinitrate (BODN). As typically found for nitrate ester-functionalized compounds, NO₂ and HONO eliminations were the most energetically favorable unimolecular paths for the parent molecule's decomposition. From there, sequences of unimolecular reactions for daughters of the initiation steps were postulated and characterized. For intermediates found to have barriers to unimolecular decomposition that would make their rate at the temperatures and time scales of interest negligible, their decomposition via H-atom abstraction and radical-addition reactions was characterized. Creating a comprehensive network that can be employed to develop a detailed finite-rate chemical kinetics mechanism for simulating BODN's decomposition, the results provide a basis for modeling BODN's combustion, as well as its response to thermal loads germane to its aging, storage, and handling.

A combined experimental and theoretical investigation of the excited-state dynamics of 2,4,6-trinitrotoluene (TNT) in DMSO solvent

In the present contribution we carried out a TDDFT and femtosecond transient absorption study of the excited state dynamics of TNT in DMSO solvent. Vertical excitation and excited state relaxation were calculated at the SMD/M06-2X/TZVP level of theory. The electron absorption spectrum for the DMSO solvated TNT was calculated and compared with the experimental results. The results of the electronic excitation energies and the spin-orbital constants imply an intersystem crossing for the S₁-T₂ transition. The femtosecond time-resolved transient absorption measurements of the TNT in DMSO show the presence of two absorption signals around 650 nm and 540 nm, which are assigned to the population in the lowest singlet and triplet excited states, S₁ and T₁, respectively. The fast decay of the S₁ state population is assigned to an efficient S₁-T₂ intersystem crossing, which soon internally converts to the T₁ state. The slow decay of the T₁ population is attributed to the nonradiative transition to the S₀ state. The combined theoretical and experimental results present a mechanistic view of the photophysical dynamics of TNT in DMSO solution.

N-oxygenation of amino compounds: Early stages in its application to the biocatalyzed preparation of bioactive compounds

Among the compounds that contain unusual functional groups, nitro is perhaps one of the most interesting due to the valuable properties it confers on pharmaceuticals and explosives. Traditional chemistry has for many years used environmentally unfriendly strategies; in contrast, the biocatalyzed production of this type of products offers a promising alternative. The small family of enzymes formed by N-oxygenases allows the conversion of an amino group to a nitro through the sequential addition of oxygen. These enzymes also make it possible to obtain other less oxidized N-O functions, such as hydroxylamine or nitroso, present in intermediate or final products. The current substrates on which these enzymes are reported to work encompass a few aromatic molecules and sugars. The unique characteristics of N-oxygenases and the great economic value of the products that they could generate, place them in a position of very high scientific and industrial interest. The most important and best studied N-oxygenases will be presented here.

Theoretical studies on the initial reaction kinetics and mechanisms of p-, m- and o-nitrotoluene

The potential energy surfaces (PESs) of three nitrotoluene isomers, such as p-nitrotoluene, m-nitrotoluene, and o-nitrotoluene, have been theoretically built at the CCSD(T)/CBS level. The geometries of reactants, transition states (TSs) and products are optimized at the B3LYP/6-311++G(d,p) level. Results show that reactions of -NO2 isomerizing to ONO, and C-NO2 bond dissociation play important roles among all of the initial channels for p-nitrotoluene and m-nitrotoluene, and that the H atom migration and C-NO2 bond dissociation are dominant reactions for o-nitrotoluene. In addition, there exist pathways for three isomer conversions, but with high energy barriers. Rate constant calculations and branching ratio analyses further demonstrate that the isomerization reactions of O transfer are prominent at low to intermediate temperatures, whereas the direct C-NO2 bond dissociation reactions prevail at high temperatures for p-nitrotoluene and m-nitrotoluene, and that H atom migration is a predominant reaction for o-nitrotoluene, while C-NO2 bond dissociation becomes important by increasing the temperature.

Insight into the chemistry of TNT during shock compression through ultrafast absorption spectroscopies

Thin films of trinitrotoluene (TNT) were shock compressed using the ultrafast laser shock apparatus at Los Alamos National Laboratory. Visible (VIS) and mid-infrared (MIR) transient absorption spectroscopies were simultaneously performed to probe for electronic and vibrational changes during shock compression of TNT. Three shock pressures (16 GPa, 33 GPa, and 45 GPa) were selected to observe no reaction, incipient reaction, and strongly developed reactions for TNT within the experimental time scale of <250 ps. Negligible absorption changes in MIR or VIS absorptions were observed at 16 GPa. At 33 GPa, MIR absorptions in the 3000 cm^-1-4000 cm^-1 range were observed to increase during the shock and continue to increase during the rarefaction, in contrast to the VIS absorption measurements, which increased during the shock and almost fully recovered during rarefaction. At 45 GPa, both VIS and MIR absorptions were strong and irreversible. The intense and spectrally broad MIR absorptions were attributed to short lived intermediates with strong, spectrally broad absorptions that dominate the spectral response. The MIR and VIS absorption changes observed at 33 GPa and 45 GPa were credited to shock induced chemistry, most likely including the formation of a very broad hydrogenic stretch feature. The results from these experiments are consistent with the chemical mechanisms that include O-H or N-H formation such as CH₃ oxidation or C-N homolysis.

Achieving tunable chemical reactivity through photo-initiation of energetic materials at metal oxide surfaces

Known applications of high energy density materials are impressively vast. Despite this, we argue that energetic materials are still underutilized for common energy purposes due to our inability to control explosive chemical reactions releasing energy from these materials. The situation appears paradoxical as energetic materials (EM) possess massive amounts of energy and, hence, should be most appropriate for applications in many energy-intensive processes. Here, we discover how chemical decomposition reactions can be stimulated with laser excitation and therefore, highly controlled by selectively designing energetic material - metal oxide interfaces with an example of pentaerythritol tetranitrate (PETN)-MgO and trinitrotoluene (TNT)-MgO composite samples. Density functional theory and embedded cluster method calculations were combined with measurements of the optical absorption spectra and laser initiation experiments. We found that the first (1064 nm, 1.17 eV), second (532 nm, 2.33 eV), and third (355 nm, 3.49 eV) laser harmonics, to all of which pure energetic materials are transparent, can be effectively used to trigger explosive reactions in the PETN-MgO samples. We propose a consistent electronic mechanism that explains how specific sub-band optical transitions initiate decomposition chemistry. Also, this selectivity reveals a fundamental difference between materials chemistry at interfaces as we show on examples of PETN and TNT energetic materials.

The thermal decomposition process of Composition B by ReaxFF/lg force field

Composition B is a melt-cast explosive consisting of mixtures of TNT and RDX. It has many excellent properties, but there are still multiple safety problems when it is used. Therefore, it is of importance to understand the thermal decomposition mechanism of Composition B. In this paper, during the establishment of the supercell model, the mass ratio of TNT to RDX is about 2:3, which accords with the actual proportion of formula of Composition B. Afterward, the thermal decomposition reaction of Composition B is conducted at various temperatures (2000 K, 2500 K, 3000 K, 3500 K, and 4000 K) by using molecular dynamics simulation of ReaxFF/lg. In terms of potential energy (PE) evolution, primary reaction, intermediate product, final product, and clusters, the thermal decomposition mechanism of Composition B is made an analysis. The activation energy of Composition B is 141.8 kJ/mol by fitting the kinetic parameters of the reaction. During the decomposition process of Composition B, the decay rate of RDX is faster than that of TNT, and the decay rates of TNT and RDX is accelerated significantly with the increasing temperature. The higher the temperature, the shorter the time difference between the two to fully decompose. It can be revealed from the result that the initial reaction path of Composition B decomposition is N-NO₂ of RDX cleavage to form NO₂, followed by the reaction of TNT with NO₂ and other molecules. The initial decomposition reaction path of Composition B is the similar at different temperatures. The main products are small molecules (NO₂, NO, N₂O, H₂O, CO₂, N₂, H₂, HNO₂, and HNO). Temperature can make a great difference for the structure of clusters. Large clusters in the system will break down into smaller molecules at high temperature.

Theoretical prediction of the trigger linkages, surface electrostatic potentials, and explosive sensitivities of 1,4-dinitroimidazole-N-oxide in the external electric fields

In order to introduce effectively the external electric fields into the explosive systems, the change trends of the strengths of trigger linkages, nitro group charges, and explosive sensitivities of 1,4-dinitroimidazole-N-oxide (1,4-DNIO) were investigated in the external electric fields at the B3LYP/6-311++G(2d,p) and M06-2X/aug-cc-pVTZ levels. The formulas for calculating the impact sensitivity by the surface electrostatic potentials were discussed. The results show that the N-NO₂ bond is always the most likely trigger linkage, followed by N → O. This is the very valuable information for the researchers engaged in the molecular design or synthesis of the energetic explosives: The influences of the weak N → O coordination bond attached to the aromatic ring on the explosive sensitivity can be ignored when the N-NO₂ bond exists. In the external electric fields along the positive directions of the N → O and C-NO₂ bond axes as well as the negative direction of the N-NO₂ bond axis, the dissociation energies (BDEs) of the N-NO₂ bond and h₅₀ values are increased, leading to the decreased impact sensitivities. The changes of the bond lengths, AIM electron density values, nitro group charges, BDEs of the trigger linkages, and impact sensitivities correlate well with the external electric field strengths, respectively. The effects of the fields on the electric spark sensitivities and shock initiation pressures are not obvious. The essence of the low BDEs of the N-NO₂ bond was revealed by the resonance theory of the aromatic ring. Graphical abstract Changes of the impact sensitivities versus field strengths.

A benchtop shock physics laboratory: Ultrafast laser driven shock spectroscopy and interferometry methods

Common Ti:sapphire chirped pulse amplified laser systems can be readily adapted to be both a generator of adjustable pressure shock waves and a source for multiple probes of the ensuing ultrafast shock dynamics. In this paper, we detail experimental considerations for optimizing the shock generation, interferometric characterization, and spectroscopic probing of shock dynamics with visible and mid-infrared transient absorption. While we have reported results using these techniques elsewhere, here we detail how the spectroscopies are integrated with the shock and interferometry experiment. The interferometric characterization uses information from beams at multiple polarizations and angles of incidence combined with thin film equations and shock dynamics to determine the shock velocity, particle velocity, and shocked refractive index. Visible transient absorption spectroscopy uses a white light supercontinuum in a reflection geometry, synchronized to the shock wave, to time resolve shock-induced changes in visible absorption such as changes to electronic structure or strongly absorbing products and intermediates due to reaction. Mid-infrared transient absorption spectroscopy uses two color filamentation supercontinuum generation combined with a simple thermal imaging microbolometer spectrometer to enable broadband single shot detection of changes in the vibrational spectra. These methods are demonstrated here in the study of shock dynamics at stresses from 5 to 30 GPa in organic materials and from a few GPa to >70 GPa in metals with spatial resolution of a few micrometers and temporal resolution of a few picoseconds. This experiment would be possible to replicate in any ultrafast laser laboratory containing a single bench top commercial chirped pulse amplification laser system.

Reversible intramolecular hydrogen transfer: a completely new mechanism for low impact sensitivity of energetic materials

The intramolecular H transfer of energetic NO₂-compounds has been recognized as a possible primary step in triggering molecular decomposition for a long time.

Adiabatic and constant volume decomposition process of condensed phase δ-1,3,5,7-tetranitro-1,3,5,7-tetrazocane at high temperatures: Quantum molecular dynamics simulations

We performed quantum molecular dynamics simulations to investigate the initiation chemistry of condensed phase δ-HMX at high temperatures by maintaining constant energy and volume to model adiabatic initiation process. The decomposition of HMX began by the C-N bond breaking in one molecule and by the C-H bond cleavage in other HMX molecule at 2400 K. At 2700 K, HMX is triggered by only one path that the C-N bond broke and the ring opened. At 3000 K, the decomposition of HMX is triggered by the C-H bond and N-O bond fission in the branch chains. There are seven decomposition channels observed during the whole decomposition stage. The N-O bond cleavage is a dominant reaction pathway. The boat configuration of the HMX molecule caused a new reaction channel to be happened by forming a new N-N bond. Another new reaction channel took place to form a new N-C bond due to intermolecular effects.

Trigger bond analysis of nitroaromatic energetic materials using wiberg bond indices

The identification of trigger bonds, bonds that break to initiate explosive decomposition, using computational methods could help direct the development of novel, "green" and efficient high energy density materials (HEDMs). Comparing bond densities in energetic materials to reference molecules using Wiberg bond indices (WBIs) provides a relative scale for bond activation (%ΔWBIs) to assign trigger bonds in a set of 63 nitroaromatic conventional energetic molecules. Intramolecular hydrogen bonding interactions enhance contributions of resonance structures that strengthen, or deactivate, the CNO₂ trigger bonds and reduce the sensitivity of nitroaniline-based HEDMs. In contrast, unidirectional hydrogen bonding in nitrophenols strengthens the bond to the hydrogen bond acceptor, but the phenol lone pairs repel and activate an adjacent nitro group. Steric effects, electron withdrawing groups and greater nitro dihedral angles also activate the CNO₂ trigger bonds. %ΔWBIs indicate that nitro groups within an energetic molecule are not all necessarily equally activated to contribute to initiation. %ΔWBIs generally correlate well with impact sensitivity, especially for HEDMs with intramolecular hydrogen bonding, and are a better measure of trigger bond strength than bond dissociation energies (BDEs). However, the method is less effective for HEDMs with significant secondary effects in the solid state. Assignment of trigger bonds using %ΔWBIs could contribute to understanding the effect of intramolecular interactions on energetic properties. © 2018 Wiley Periodicals, Inc.

Numerical analysis of thermal decomposition for RDX, TNT, and Composition B

Demilitarization of waste explosives on a commercial scale has become an important issue in many countries, and this has created a need for research in this area. TNT, RDX and Composition B have been used as military explosives, and they are very sensitive to thermal shock. For the safe waste treatment of these high-energy and highly sensitive explosives, the most plausible candidate suggested has been thermal decomposition in a rotary kiln. This research examines the safe treatment of waste TNT, RDX and Composition B in a rotary kiln type incinerator with regard to suitable operating conditions. Thermal decomposition in this study includes melting, 3 condensed phase reactions in the liquid phase and 263 gas phase reactions. Rigorous mathematical modeling and dynamic simulation for thermal decomposition were carried out for analysis of dynamic behavior in the reactor. The results showed time transient changes of the temperature, components and mass of the explosives and comparisons were made for the 3 explosives. It was concluded that waste explosives subject to heat supplied by hot air at 523.15K were incinerated safely without any thermal detonation.

Gas phase ion chemistry of an ion mobility spectrometry based explosive trace detector elucidated by tandem mass spectrometry

The gas phase ion chemistry for an ion mobility spectrometer (IMS) based explosive detector has been elucidated using tandem mass spectrometry. The IMS system, which is operated with hexachloroethane and isobutyramide reagent gases and an ion shutter type gating scheme, is connected to the atmospheric pressure interface of a triple quadrupole mass spectrometer (MS/MS). Product ion masses, daughter ion masses, and reduced mobility values for a collection of nitro, nitrate, and peroxide explosives measured with the IMS/MS/MS instrument are reported. The mass and mobility data together with targeted isotopic labeling experiments and information about sample composition and reaction environment are leveraged to propose molecular formulas, structures, and ionization pathways for the various product ions. The major product ions are identified as [DNT-H](-) for DNT, [TNT-H](-) for TNT, [RDX+Cl](-) and [RDX+NO2](-) for RDX, [HMX+Cl](-) and [HMX+NO2](-) for HMX, [NO3](-) for EGDN, [NG+Cl](-) and [NG+NO3](-) for NG, [PETN+Cl](-) and [PETN+NO3](-) for PETN, [HNO3+NO3](-) for NH4NO3, [NO2](-) for DMNB, [HMTD-NC3H6O3+H+Cl](-) and [HMTD+H-CH2O-H2O2](+) for HMTD, and [(CH3)3CO2](+) for TATP. In general, the product ions identified for the IMS system studied here are consistent with the product ions reported previously for an ion trap mobility spectrometer (ITMS) based explosive trace detector, which is operated with dichloromethane and ammonia reagent gases and an ion trap type gating scheme. Differences between the explosive trace detectors include the [NG+Cl](-) and [PETN+Cl](-) product ions being major ions in the IMS system compared to minor ions in the ITMS system as well as the major product ion for TATP being [(CH3)3CO2](+) for the IMS system and [(CH3)2CNH2](+) for the ITMS system.

Decomposition of condensed phase energetic materials: interplay between uni- and bimolecular mechanisms

Activation energy for the decomposition of explosives is a crucial parameter of performance. The dramatic suppression of activation energy in condensed phase decomposition of nitroaromatic explosives has been an unresolved issue for over a decade. We rationalize the reduction in activation energy as a result of a mechanistic change from unimolecular decomposition in the gas phase to a series of radical bimolecular reactions in the condensed phase. This is in contrast to other classes of explosives, such as nitramines and nitrate esters, whose decomposition proceeds via unimolecular reactions both in the gas and in the condensed phase. The thermal decomposition of a model nitroaromatic explosive, 2,4,6-trinitrotoluene (TNT), is presented as a prime example. Electronic structure and reactive molecular dynamics (ReaxFF-lg) calculations enable to directly probe the condensed phase chemistry under extreme conditions of temperature and pressure, identifying the key bimolecular radical reactions responsible for the low activation route. This study elucidates the origin of the difference between the activation energies in the gas phase (~62 kcal/mol) and the condensed phase (~35 kcal/mol) of TNT and identifies the corresponding universal principle. On the basis of these findings, the different reactivities of nitro-based organic explosives are rationalized as an interplay between uni- and bimolecular processes.

Volatilization interference in thermal analysis and kinetics of low-melting organic nitro compounds

DNTF is the most sensitive to heat while DNAN has the best thermal stability.

Decomposition mechanisms and kinetics of novel energetic molecules BNFF-1 and ANFF-1: quantum-chemical modeling

Decomposition mechanisms, activation barriers, Arrhenius parameters, and reaction kinetics of the novel explosive compounds, 3,4-bis(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole (BNFF-1), and 3-(4-amino-1,2,5-oxadiazol-3-yl)-4-(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole (ANFF-1) were explored by means of density functional theory with a range of functionals combined with variational transition state theory. BNFF-1 and ANFF-1 were recently suggested to be good candidates for insensitive high energy density materials. Our modeling reveals that the decomposition initiation in both BNFF-1 and ANFF-1 molecules is triggered by ring cleavage reactions while the further process is defined by a competition between two major pathways, the fast C-NO₂ homolysis and slow nitro-nitrite isomerization releasing NO. We discuss insights on design of new energetic materials with targeted properties gained from our modeling.