Main Decomposition Channel Research Articles

Comparative study on the thermal decomposition of structural isomers: Pyrazole and imidazole energetic materials

Exploration of the thermal decay mechanisms of energetic skeletons supports the understanding of stability and energy release. Herein, we comparatively investigated the thermal decomposition of energetic isomers nitropyrazole and nitroimidazoles at high temperature and high density based on ReaxFF-lg reactive molecular dynamics simulations, which have not been fully understood. Results show that the initial decomposition reaction of nitropyrazole and nitroimidazole were triggered by the OH elimination as a result of intermolecular H-shift. And the N2 elimination plays a major role in the decomposition of pyrazoles, while the formation of hydrogen cyanide CHN is the main decomposition channel of imidazoles. Another important channel of their nitro derivatives is C-NO2 bond dissociation. At high density, the cleavage of C-NO2 bonds is inhibited, and the reactions between molecules are promoted, therefore the dimers are easier to produce. Detailed evolution yields of key intermediates, final gaseous products, and clusters are also presented to study the difference in the thermal decay of pyrazoles and imidazoles, as well as the effect of pressure. Overall, these thermolysis properties of nitropyrazole and nitroimidazole are expected to gain more knowledge to the diversity of thermal decomposition of energetic isomers.

Stone—Wales Graphane: Its Structure, Properties, and Thermal Stability

A new two-dimensional hydrocarbon material formed upon complete chemical bonding of hydrogen to the both sides of Stone-Wales graphene, which is a recently predicted new allotrope of graphene, is numerically studied. The band gap Eg = 5.48 eV, the binding energy, and bond lengths, as well as the electron and phonon densities states, are determined. The anisotropy of the Young modulus is revealed. The heating-induced processes of defect formation are studied by the real-time molecular dynamics method. It is shown that the main thermal decomposition channel is the desorption of atomic hydrogen. The second most important decomposition channel is the desorption of molecular hydrogen. For the main decomposition channel, the activation energy Ea = 2.62 eV and the frequency-dependent factor A = 1.1 × 1018 s−1 in the Arrhenius law are determined.

Reaction between Peroxy and Alkoxy Radicals Can Form Stable Adducts.

Peroxy (RO2) and alkoxy (RO) radicals are prototypical intermediates in any hydrocarbon oxidation. In this work, we use computational methods to (1) study the mechanism and kinetics of the RO2 + OH reaction for previously unexplored “R” structures (R = CH(O)CH2 and R = CH3C(O)) and (2) investigate a hitherto unaccounted channel of molecular growth, R′O2 + RO. On the singlet surface, these reactions rapidly form ROOOH and R′OOOR adducts, respectively. The former decomposes to RO + HO2 and R(O)OH + O2 products, while the main decomposition channel for the latter is back to the reactant radicals. Decomposition rates of R′OOOR adducts varied between 103 and 0.015 s–1 at 298 K and 1 atm. The most long-lived R′OOOR adducts likely account for some fraction of the elemental compositions detected in the atmosphere that are commonly assigned to stable covalently bound dimers.

An ab initio study on noble gas inserted halogenated acetylene: HNgCCX (Ng\u2009=\u2009Kr and Xe; X\u2009=\u2009halogen)

Although HNgCCX (Ng = Kr and Xe; X = F and Cl) have been identified in cryogenic matrices, similar Br and I analogues have not been prepared so far. In this paper, the nature of HNgCCX (Ng = Kr and Xe; X = F, Cl, Br and I) have been investigated by ab initio methods. The main characteristic absorption peak of HNgCCX is the vH-Ng, which decreases as X varies from F to I. Moreover, the H-Xe bond is stronger than the H-Kr bond. The vC≡C and vC-X exhibit red- and blue-shift characters, respectively, especially the C-X bond is abnormal blue-shift halogen bond. AIM results show that the H-Ng bond is essentially covalent bond and the covalent character of H-Xe bond is underestimated, and the trend of the covalent character is C-Cl > C-Br > C-F > C-I. Although HNgCCX is instable thermodynamically with respect to Ng + HCCX, it is kinetically stable with respect to the two-/three-body channels due to the relatively larger energy barriers. The three-body channels of HNgCCX is the main decomposition channel, and the kinetically stability of HXeCCX is more than its Kr analogues. This study is helpful for the preparation of new HNgCCX in cryogenic matrices.

Theoretical investigation of germane and germylene decomposition kinetics

The dissociation kinetics of germane and its decomposition products were studied determining microcanonical kinetic constants with RRKM theory and integrating the master equation using a stochastic approach. Relevant reaction parameters were calculated through first principles calculations. Structures of reactants and transition states were determined at the B3LYP/aug-cc-pvtz level while energies were computed at the CCSD(T) level and extended to the complete basis set limit. Though similar for many aspects to the kinetics of decomposition of SiH(4), GeH(4) has some peculiar features that indicate a different chemical reactivity. It was found that the main decomposition channel leads to the formation of germylene, GeH(2), which rapidly decomposes to atomic Ge and H(2). The dissociation of GeH(2) to Ge and H(2) is a formally spin forbidden reaction characterized by an activation energy of 160.3 kJ mol(-1) calculated at the minimum energy crossing point between the singlet and triplet states. The intersystem crossing probability was explicitly included in the microcanonical simulations through Landau-Zener theory. It was found that its effect on the reaction rate is almost negligible, both because of the large spin-orbit coupling between the singlet and triplet states and for the fall off conditions prevailing in the examined pressure and temperature ranges. Kinetic constants of the main decomposition channels were determined as a function of pressure and temperature between 0.0013 and 10 bar and 1100 and 1700 K. The high and low pressure kinetic constants for GeH(4) decomposition are 6.4 x 10(13) (T/K)(0.272) exp(-26 700 K/T) and 2.7 x 10(48) (T/K)(-9.05) exp(-31 600 K/T), while those for GeH(2) are 6.02 x 10(12) (T/K)(0.203) exp(-19 660 K/T) and 1.6 x 10(26) (T/K)(-3.06) exp(-21 121 K/T), respectively. A quantitative agreement with experimental data for GeH(4) decomposition could be obtained adopting a downward energy transfer parameter of 340 x (T/298 K)(0.85) cm(-1) in the collisional model, and assuming that atomic Ge can react fast with GeH(4) to form Ge(2)H(2) and H(2), thus enhancing the germane decomposition rate and suggesting that a fast kinetic route leading to the Ge(2)H(2) production can be active in the gas phase.

X-ray Absorption Spectromicroscopy Study of UV-Photoinduced Surface Modification and Anisotropy in Polyimide Films

X-ray absorption spectromicroscopy with an X-ray photoelectron emission microscope (X-PEEM) was applied to study the modification of polyimide films by linear polarized deep ultraviolet (LPDUV) light, using LPDUV-patterned (0.4−1 J/cm2) CBDA-ODA samples as a test system. Stacks of successive X-PEEM images were collected in the total electron yield acquisition mode over the photon energy ranges containing the relevant C, N, and O K-edges. The LPDUV-induced patterns could be clearly distinguished in the images acquired at the excitation energies of characteristic absorption resonances. The analysis of these images and the derived NEXAFS microspectra suggests that the LPDUV irradiation causes an anisotropic decomposition of the PI backbone with the cleavage of the cyclobutane ring to form a maleimide structure as the main decomposition channel. Whereas the UV-induced anisotropy was not directly perceptible in the X-PEEM images acquired at the excitation energies of characteristic absorption resonances, it could be clearly seen and evaluated in the corresponding microspectra. In particular, the dichroic ratio of the π(CO*) resonance of imide was found to be ≈6%, in good agreement with previous spectroscopic results.

Theoretical investigation of unimolecular decomposition channels of furan4

Density functional theory and high-level ab initio calculations were carried out to investigate three unimolecular decomposition channels of furan. All equilibrium and transition state structures along the proposed decomposition channels are fully optimized by B3LYP/6-31G** and characterized at the same level of theory by vibrational and intrinsic reaction coordinate analyses. Relative energies of the optimized structures were evaluated at theoretical levels up to QCISD(T)/6-311++G**. The theoretical results suggest that the unimolecular decomposition channel of isoxazole, proposed in an experimental study and implied to be the main decomposition channel of furan, is responsible only for the formation of HC(TRIPLE BOND)CH and H2O(DOUBLE BOND)C(DOUBLE BOND)O, minor products of furan thermal decomposition. A new decomposition mechanism, proposed in the present study, is shown to be more likely responsible for the formation of CH3C(TRIPLE BOND)CH and CO, major products of furan thermal decomposition. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 240–249, 1998

Computational Studies of the Isomerization Pathways of Isocyanic Acid HNCO

Abstract Paths of isomerizations of isocyanic acid HNCO into various chain isomers via ring intermediates have been investigated by ab initio MO calculations with the MRD-CI procedure employing the 6-31G** basis sets. Geometry optimizations were accomplished at the RHF, UHF, or CASSCF level of theory. It is found that the isomerization from HNCO to cyanic acid HOCN is energetically the most favorable and that it should proceed via successive 1,2-hydrogen migrations rather than by a single 1,3-hydrogen migration. The overall barrier height is calculated to be 423 kJ mol−1, which is ca. 60 kJ mol−1 higher than the critical energy for the main decomposition channel, HNCO→NH(3Σ)+CO. Implications of the results to the kinetics of the thermal decompostion of HNCO at high temperatures are discussed.

Study of anion-radicals of carboranes-12 in the gas phase by the mass spectrometry method of the resonance capture of electrons

1. The molecules of o-carboranes-12 form in the gas phase long-lived negative molecular ions by the resonance capture of electrons with thermal and epithermal energies; their main decomposition channel is autocleavage of an electron. 2. Isomerization of the carborane skeleton to the o-isomer occurs not only in the case of the dianions in solution, but also in the step of forming the anion-radical.