Decomposition Of Nitromethane Research Articles

A mechanistical study on non-equilibrium reaction pathways in solid nitromethane (CH3NO2) and D3-nitromethane (CD3NO2) upon interaction with ionizing radiation

Thin films of homogeneously mixed nitromethane (CH3NO2) and D3-nitromethane (CD3NO2) ices were exposed to energetic electrons and Lyman α photons. The isotopically mixed reaction products were probed in situ via reflectron time-of-flight mass spectrometry coupled with pulsed photoionization during temperature programmed desorption. This study provides compelling evidence on three high energy pathways, which have not been observed under collisionless conditions in the gas phase. These are decomposition of nitromethane (CH3NO2) via atomic oxygen loss to nitrosomethane (CH3NO), fragmentation of nitromethane (CH3NO2) and/or methylnitrite (CH3ONO) via carbene (CH2) loss, and carbonhydrogen bond rupture processes in nitromethane (CH3NO2) and/or methylnitrite (CH3ONO).

Thermal Dissociation and Roaming Isomerization of Nitromethane: Experiment and Theory.

The thermal decomposition of nitromethane provides a classic example of the competition between roaming mediated isomerization and simple bond fission. A recent theoretical analysis suggests that as the pressure is increased from 2 to 200 Torr the product distribution undergoes a sharp transition from roaming dominated to bond-fission dominated. Laser schlieren densitometry is used to explore the variation in the effect of roaming on the density gradients for CH3NO2 decomposition in a shock tube for pressures of 30, 60, and 120 Torr at temperatures ranging from 1200 to 1860 K. A complementary theoretical analysis provides a novel exploration of the effects of roaming on the thermal decomposition kinetics. The analysis focuses on the roaming dynamics in a reduced dimensional space consisting of the rigid-body motions of the CH3 and NO2 radicals. A high-level reduced-dimensionality potential energy surface is developed from fits to large-scale multireference ab initio calculations. Rigid body trajectory simulations coupled with master equation kinetics calculations provide high-level a priori predictions for the thermal branching between roaming and dissociation. A statistical model provides a qualitative/semiquantitative interpretation of the results. Modeling efforts explore the relation between the predicted roaming branching and the observed gradients. Overall, the experiments are found to be fairly consistent with the theoretically proposed branching ratio, but they are also consistent with a no-roaming scenario and the underlying reasons are discussed. The theoretical predictions are also compared with prior theoretical predictions, with a related statistical model, and with the extant experimental data for the decomposition of CH3NO2, and for the reaction of CH3 with NO2.

Lyman α photolysis of solid nitromethane (CH3NO2) and D3-nitromethane (CD3NO2)--untangling the reaction mechanisms involved in the decomposition of model energetic materials.

Solid nitromethane (CH3NO2) along with its isotopically labelled counterpart D3-nitromethane (CD3NO2) ices were exposed to Lyman α photons to investigate the mechanism involved in the decomposition of energetic materials in the condensed phase. The chemical processes in the ices were monitored online and in situ via infrared spectroscopy complimented by temperature programmed desorption studies utilizing highly sensitive reflectron time-of-flight mass spectrometry coupled with pulsed photoionization (ReTOF-PI) at 10.49 eV. The infrared data revealed the formation of cis-methylnitrite (CH3ONO), formaldehyde (H2CO), water (H2O), carbon monoxide (CO), and carbon dioxide (CO2). Upon sublimation of the irradiated samples, three classes of higher molecular weight products, which are uniquely formed in the condensed phase, were identified via ReTOF-PI: (i) nitroso compounds [nitrosomethane (CH3NO), nitrosoethane (C2H5NO), nitrosopropane (C3H7NO)], (ii) nitrite compounds [methylnitrite (CH3ONO), ethylnitrite (C2H5ONO), propylnitrite (C3H7ONO)], and (iii) higher molecular weight molecules [CH3NONOCH3, CH3NONO2CH3, CH3OCH2NO2, ONCH2CH2NO2]. The mechanistical information obtained in the present study suggest that the decomposition of nitromethane in the condensed phase is more complex compared to the gas phase under collision-free conditions opening up not only hitherto unobserved decomposition pathways of nitromethane (hydrogen atom loss, oxygen atom loss, retro carbene insertion), but also the blocking of several initial decomposition steps due to the 'matrix cage effect'.

Effect of diethylenetriamine on the structure of detonation waves in nitromethane

This paper presents the results of experimental studies of the reaction zone structure in steady-state detonation of nitromethane sensitized by diethylenetriamine (DETA). The concentration of DETA was varied within 0.0125–15%. It is shown that small additions of DETA lead to a qualitative change in the flow pattern in the reaction zone. After the shock, the mass flow rate continues to increase for about 10 ns, reaches a maximum, and only then decreases. The amplitude of the chemical spike decreases by an order of magnitude. These features are explained by the decomposition of nitromethane sensitized by DETA in front of the shock wave, which is due to a sharp increase in the initial reaction rate.

Analysis of nitromethane thermal decomposition at low temperatures

The thermal decomposition of nitromethane (NM) over the temperature range from 580 to 700 K at pressures of 4 Torr to 40 atm was analyzed. On the basis of literature data, with the use of theoretical transitional curves of the modified Kassel integral, the rate constants k of NM decomposition at the upper pressure limit were determined. The values thus obtained are in good agreement with the results of extrapolation of the high-temperature (1000–1400 K) k1, ∞ values to lower temperatures. The reasons for which the NM decomposition rate constants differ by two orders of magnitude at low temperatures are considered. A general expression for the NM decomposition rate constant at the upper pressure limit over the 580–1400 K temperature range was determined: k1, ∞ = (1.8 ± 0.7) × 1016 exp((−58.5 ± 2)/RT) s−1. These data disprove the hypothesis that a nitro-nitrite rearrangement takes place during the NM decomposition at low temperatures.

The effect of pressure on thermal decomposition of solid nitromethane via MD simulation

The thermal decomposition of solid nitromethane (NM) is studied by ReaxFF molecular dynamics simulations to obtain the time evolution of the mechanism of NM under high temperature and pressure. It is determined that the initial decomposition mechanism of NM is dependent on pressure effect. In the 0–3 GPa pressure regime, the initial reactions is the C–N bond dissociation and the unimolecular rearrangement connecting between NM and methyl nitrite isomers; in the 4–7 GPa, the initial pathways of NM are the intermolecular proton transfer and C–N, C–O bond rupture. In the secondary reactions step, several fragments, like H2O, NO, NO2, HONO, play a role of catalysis. The product decomposition of NM contains many different structures of carbon clusters, and the configuration of cluster is dependent on pressure.

Enhanced Thermal Decomposition of Nitromethane on Functionalized Graphene Sheets: Ab Initio Molecular Dynamics Simulations

The burning rate of the monopropellant nitromethane (NM) has been observed to increase by adding and dispersing small amounts of functionalized graphene sheets (FGSs) in liquid NM. Until now, no plausible mechanisms for FGSs acting as combustion catalysts have been presented. Here, we report ab initio molecular dynamics simulations showing that carbon vacancy defects within the plane of the FGSs, functionalized with oxygen-containing groups, greatly accelerate the thermal decomposition of NM and its derivatives. This occurs through reaction pathways involving the exchange of protons or oxygens between the oxygen-containing functional groups and NM and its derivatives. FGS initiates and promotes the decomposition of the monopropellant and its derivatives, ultimately forming H(2)O, CO(2), and N(2). Concomitantly, oxygen-containing functional groups on the FGSs are consumed and regenerated without significantly changing the FGSs in accordance with experiments indicating that the FGSs are not consumed during combustion.

Kinetics of $$\dot NO_2$$ formation upon the decomposition of nitromethane behind shock waves and the possibility of nitromethane isomerization in the course of the reaction

The decomposition of nitromethane behind shock waves was studied at T = 1190–1490 K and P ≈ 1.5 atm; the reaction was monitored based on the formation and consumption of \(\dot NO_2\), radicals, which were detected by their absorption in the region of λ = 405 nm. It was found that the curves of the yield of \(\dot NO_2\) have a convex shape, which is characteristic of the formation of primary decomposition products. Based on an analysis of the initial sections of the experimental curves of the yield of \(\dot NO_2\), the temperature dependence of the rate constants of formation of these radicals upon the decomposition of nitromethane was found for the first time: \(k_1 (\dot NO_2 ) = (6.3 \pm 2) \times 10^{12} \exp ( - 48.9 \pm 2/RT)s^{ - 1}\) (the dimensionality of Ea is kcal/mol). It was found that the rate constants of nitromethane decomposition measured from the consumption of the parent substance and the yield of \(\dot NO_2\) radicals almost coincide with each other. A kinetic simulation of the formation and consumption of \(\dot NO_2\) upon the decomposition of nitromethane was performed. A good agreement between experimental and calculated data was achieved. A brief theoretical analysis of competition between the channels of direct disintegration and isomerization under conditions of the thermal decomposition of nitromethane was performed. The advantage of the direct disintegration channel with the rupture of the C-N bond was shown. Both experimental and published data on the isomerization of nitromethane into methyl nitrite upon its thermal decomposition and photolysis were analyzed.

Finite-Length Effect of Carbon Nanotubes on the Encapsulation and Decomposition of Nitromethane: ONIOM Calculation

To understand the confinement effect of carbon nanotubes (CNTs) on energetic compounds, the encapsulation and thermal decomposition of nitromethane (NM) confined inside finite armchair (5,5) single-walled CNTs of various lengths (C30+10nH20) were investigated on the basis of ONIOM calculations. It was found that NM was not encapsulated by CNT(5,5) of n ≤ 5, while CNT(5,5) of n≥ 6 were able to encapsulate NM. The NM confined inside the CNT(5,5) displayed different structural characteristics in contrast to the isolated NM. The activation energy barriers of the C-N thermal decomposition for the confined NM were found to be about 5˜15 kcal/mol lower than that of the isolated NM, suggesting that CNT confinement enabled the C-N thermal decomposition of NM to take place more easily. In addition, our computations showed that a distinct oscillation of the activation energy barriers was correlated to tube length increase, especially when n≤ 10. This indicated that the energy barrier was highly dependent on CNT length. Keywords: Carbon nanotube, Nitromethane, Thermal decomposition, Confinement effect, Bond dissociation energy, Ab initio, encapsulation, ONIOM calculation, energetic compounds, energy barrier

Thermal Decomposition of Condensed-Phase Nitromethane from Molecular Dynamics from ReaxFF Reactive Dynamics

We studied the thermal decomposition and subsequent reaction of the energetic material nitromethane (CH(3)NO(2)) using molecular dynamics with ReaxFF, a first principles-based reactive force field. We characterize the chemistry of liquid and solid nitromethane at high temperatures (2000-3000 K) and density 1.97 g/cm(3) for times up to 200 ps. At T = 3000 K the first reaction in the decomposition of nitromethane is an intermolecular proton transfer leading to CH(3)NOOH and CH(2)NO(2). For lower temperatures (T = 2500 and 2000 K) the first reaction during decomposition is often an isomerization reaction involving the scission of the C-N bond the formation of a C-O bond to form methyl nitrate (CH(3)ONO). Also at very early times we observe intramolecular proton transfer events. The main product of these reactions is H(2)O which starts forming following those initiation steps. The appearance of H(2)O marks the beginning of the exothermic chemistry. Recent quantum-mechanics-based molecular dynamics simulations on the chemical reactions and time scales for decomposition of a crystalline sample heated to T = 3000 K for a few picoseconds are in excellent agreement with our results, providing an important, direct validation of ReaxFF.

Low-temperature exfoliation of multilayer-graphene material from FeCl3 and CH3NO2 co-intercalated graphite compound

Microwave induced rapid decomposition of nitromethane at low temperature exfoliates the graphene sheets from the FeCl(3) and CH(3)NO(2) co-intercalated graphite compound without creating many defects and functional groups. This approach provides a scalable method for high-quality graphene materials via low-temperature exfoliation of graphite under mild chemical conditions.

Decomposition of nitromethane in shock waves: The primary stage and the kinetics of decomposition at pressures of about 40 atm

The kinetics of nitromethane (NM) decomposition and the observed rate constant of the process were measured behind reflected shock wave using absorption spectroscopy at λ = 230 nm, temperatures of 1060 to 1350 K, pressure of ∼40 atm, and initial reactant concentration within 30–100 ppm. It was observed that, at the initial stage, nitromethane decomposes exponentially, without autoacceleration. The results of numerical simulations with the help of three most known kinetic schemes of nitromethane decomposition proved to be in close to agreement with our experimental data over the entire temperature range covered. It was demonstrated that the measured rate constant is identical to the rate constant of the dissociation CH3NO2 → CH3 + NO2. The temperature dependence of k1 was approximated by the Arrhenius formula k1 = 2.57 × 1014 exp(−52.85/RT) s−1 (activation energy in kcal/mol), which suggests that the nitromethane dissociation proceeds in the falloff pressure region.

Nitromethane Decomposition under High Static Pressure

The room-temperature pressure-induced reaction of nitromethane has been studied by means of infrared spectroscopy in conjunction with ab initio molecular dynamics simulations. The evolution of the IR spectrum during the reaction has been monitored at 32.2 and 35.5 GPa performing the measurements in a diamond anvil cell. The simulations allowed the characterization of the onset of the high-pressure reaction, showing that its mechanism has a complex bimolecular character and involves the formation of the aci-ion of nitromethane. The growth of a three-dimensional disordered polymer has been evidenced both in the experiments and in the simulations. On decompression of the sample, after the reaction, a continuous evolution of the product is observed with a decomposition into smaller molecules. This behavior has been confirmed by the simulations and represents an important novelty in the scene of the known high-pressure reactions of molecular systems. The major reaction product on decompression is N-methylformamide, the smallest molecule containing the peptide bond. The high-pressure reaction of crystalline nitromethane under irradiation at 458 nm was also experimentally studied. The reaction threshold pressure is significantly lowered by the electronic excitation through two-photon absorption, and methanol, not detected in the purely pressure-induced reaction, is formed. The presence of ammonium carbonate is also observed.

Effect of Chirality and Size on the Thermal Decomposition of Nitromethane Confined inside Single-Walled Carbon Nanotube

The molecular structure and thermal decomposition of nitromethane confined inside armchair (CNT(5,5),CNT(6,6),CNT(8,8)) and zigzag (CNT(9,0),CNT(10,0),CNT(11,0)) single-walled carbon nanotubes (CNTs) with different diameters were investigated using the ONIOM (B3LYP/6-311++G:UFF) method.Results showed that the Cs symmetry of nitromethane confined inside CNT(5,5) and CNT(9,0) was destroyed and that the C—N bond was compressed slightly.Confinement in CNT(6,6),CNT(8,8),CNT(10,0),and CNT(11,0) had no evident influence on the molecular structure of nitromethane.By analyzing the potential energy surface along the C—N bond,we found that a transition state existed during the thermal decomposition of nitromethane confined inside CNT(5,5) and CNT(9,0).This was very different from the behavior of the nitromethane monomer as no transition state existed during C—N bond dissociation.The activation energy barriers of the thermal decomposition for nitromethane confined inside CNT(5,5) and CNT(9,0) were found to be lower by about 71 and 58 kJ·mol-1,respectively,compared with the bond dissociation energy of the nitromethane monomer.Confinement in CNT(6,6) and CNT(8,8) resulted in a slight decrease in the activation energy.Confinement in CNT(8,8) and CNT(11,0) did not affect the thermal decomposition of nitromethane.We concluded that the activation energy of nitromethane decomposition was significantly reduced by confinement in a carbon nanotube with a small diameter.Additionally,the activation energy was not influenced by the chirality of the carbon nanotube.

Rearrangement and thermal decomposition of nitromethane confined inside an armchair (5, 5) single-walled carbon nanotube

In this work, the thermal decomposition and rearrangement of nitromethane (NMT) confined inside an armchair (5, 5) single-walled carbon nanotubes [CNT(5.5)] were investigated by using the ONIOM calculations in order to understand the confinement effect of CNT on the initial reactions of nitro-energetic compounds. We found that the activation energy barriers for the NMT–MNT (methyl nitrite) rearrangement, H-migration rearrangement and C–N homolytic dissociation were significantly decreased by the confinement effect of CNT(5, 5), suggesting that the CNT(5, 5) can promote the rearrangement and thermal decomposition reactions of the NMT. In both the isolated and confined cases, the C–N homolytic cleavage was kinetically favorable in view of the relatively low activation barrier. However, the energy barrier of the NMT–MNT rearrangement was lower than that of the H-migration rearrangement reaction due to their confinement in CNT(5, 5). Furthermore, the relative energies of the intermediates generated from the rearrangement and thermal decomposition were also modified by the confinement of CNT(5, 5).

Theoretical study on the thermal decomposition of nitromethane encapsulated inside single-walled carbon nanotubes

In this work, the molecular structures and the thermal decomposition of nitromethane (NM) encapsulated inside armchair (5, 5), (6, 6), and (8, 8) single-walled carbon nanotubes were investigated on the basis of the ONIOM calculations in order to understand the effect of CNT encapsulation on the energetic compound. The results show that the NM encapsulated inside CNT(5, 5) has a different geometry with respect to the isolated NM. The molecular structure of NM is not evidently affected by the encapsulation of CNT(6, 6) and CNT(8, 8). The activation energy barriers of the C–N thermal decomposition for the NM encapsulated inside CNT(5, 5) are found to be lower of about ∼17 kcal/mol than the C–N bond dissociation energy of the isolated NM, indicating that the CNT(5, 5) can promote the C–N thermal decomposition of encapsulated NM. In the cases of CNT(6, 6) and CNT(8, 8), the energy barriers to be overcome for the C–N bond thermal decomposition are very similar to the value of the isolated NM. The effect of encapsulation energy and CNT polarizability are expected to be responsible for the variation of the C–N dissociation activation energy for the NM encapsulated inside CNT with different diameter.

DFT Study of deNOx Reactions in the Gas Phase: Mimicking the Reaction Mechanism over BaNaY Zeolites

Neutral and ionic pathways for aci-nitromethane decomposition were studied in the gas phase, and the Gibbs free energy surfaces were constructed at 473 K. The pathways studied were based on proposed mechanisms of NO(x) reduction by acetaldehyde over BaNaY zeolites. Density functional theory at the B3LYP/6-311++G(d,p) level of theory was used, and 29 stable intermediates and 39 transition states were identified and quantified. Plausible pathways involving unimolecular decomposition or NO(2) addition were both explored. The rate constants for all elementary steps were estimated using transition state theory, and kinetic modeling was carried out to identify the dominant reaction channel. For the ionic routes, one of the NO(2) addition pathways dominated at typical NO(2) concentrations. For the neutral routes, one of the unimolecular decomposition routes was dominant. A solvation model was then included to mimic the environment of the BaNaY zeolite catalyst in a simplified manner. While inclusion of solvation effects stabilized the ionic species significantly, the dominant reaction channels in both the neutral and ionic systems were not altered. Our results show that the addition of NO(2) facilitates the decomposition of aci-anion nitromethane.

First-principles study of thermal decomposition of liquid nitromethane and its compressive effect

Based on the framework of density functional theory，we employed the first-principles molecular dynamics to simulate the thermal decomposition of liquid nitromethane and obtained the time-evolution for the population of decomposition productions. We discussed the three possible reactions at the initial stage of thermal decomposition: intramolecule proton transfer reacton, intermolecule proton transfer reaction, and C—N bond rupture. We also studied the dynamic behavior of thermal decomposition of liquid nitromethane under different density （pressure） conditions. We found that the thermal decomposition of liquid nitromethane sensitively depends on the liquid density of pressure. A possible explanation was given.

Microscopic Approaches to Liquid Nitromethane Detonation Properties

In this paper, thermodynamic and chemical properties of nitromethane are investigated using microscopic simulations. The Hugoniot curve of the inert explosive is computed using Monte Carlo simulations with a modified version of the adaptative Erpenbeck equation of state and a recently developed intermolecular potential. Molecular dynamic simulations of nitromethane decomposition have been performed using a reactive potential, allowing the calculation of kinetic rate constants and activation energies. Finally, the Crussard curve of detonation products as well as thermodynamic properties at the Chapman-Jouguet (CJ) point are computed using reactive ensemble Monte Carlo simulations. Results are in good agreement with both thermochemical calculations and experimental measurements.

Crystal Structure of Nitromethane up to the Reaction Threshold Pressure

Angle dispersion X-ray diffraction (AXDX) experiments on nitromethane single crystals and powder were performed at room temperature as a function of pressure up to 19.0 and 27.3 GPa, respectively, in a membrane diamond anvil cell (MDAC). The atomic positions were refined at 1.1, 3.2, 7.6, 11.0, and 15.0 GPa using the single-crystal data, while the equation of state (EOS) was extended up to 27.3 GPa, which is close to the nitromethane decomposition threshold pressure at room temperature in static conditions. The crystal structure was found to be orthorhombic, space group P2(1)2(1)2(1), with four molecules per unit cell, up to the highest pressure. In contrast, the molecular geometry undergoes an important change consisting of a gradual blocking of the methyl group libration about the C-N bond axis, starting just above the melting pressure and completed only between 7.6 and 11.0 GPa. Above this pressure, the orientation of the methyl group is quasi-eclipsed with respect to the NO bonds. This conformation allows the buildup of networks of strong intermolecular O...H-C interactions mainly in the bc and ac planes, stabilizing the crystal structure. This structural evolution determines important modifications in the IR and Raman spectra, occurring around 10 GPa. Present measurements of the Raman and IR vibrational spectra as a function of pressure at different temperatures evidence the existence of a kinetic barrier for this internal rearrangement.