Formation of a detonation wave in the thermal decomposition of acetylene

The formation of a condensation detonation wave has been experimentally observed in the shock-induced thermal decomposition of acetylene. The stable detonation wave in the 20% C₂H₂ + 80% Ar mixture has been obtained at an initial pressure behind the shock wave of no less than 30 atm. The main kinetic characteristics of the pyrolysis of acetylene—the period of the induction of condensation and the growth rate constant of condensed particles—have been determined. The correlation of various stages of the process with the heat release in the condensation has been analyzed. It has been shown that the period of the particle growth induction is not accompanied by noticeable heat release. The subsequent condensation stages characterized by significant heat release occur very rapidly (faster than 10⁻⁵ s) in the so-called explosive condensation. The analysis of the results indicates that the reactions leading to the growth of large polyhydrocarbon molecules, which precede the formation of condensed carbon particles, constitute the limiting stage of the process, which determines the possibility of the formation of the condensation detonation wave in acetylene. An increase in the pressure is accompanied by the sharp narrowing of the induction region and the transition of the process to the condensation detonation wave.     

Specific features of explosive decomposition of pentaerythritol tetranitrate exposed to an electron beam with an explosive emission cathode

A comparative examination of the critical energy density of explosive decomposition of pentaerythritol tetranitrate exposed either to an electron beam of a GIN-600 accelerator (240 keV, 20 ns) with an explosive emission cathode or to this beam combined with metal low-temperature diode plasma has been performed. It has been demonstrated that the contribution of plasma to the development of explosive decomposition is appreciable at explosion probabilities P ≤ 0.2. At higher energy densities and explosion probabilities P ≥ 0.5, the contribution of plasma to the overall beam energy density did not exceed 10%.     

High time resolution spectroscopy studies of the explosive decomposition of silver azide

We have analyzed the existing assumptions about the mechanism of the explosive decomposition of the heavy metal azides. We present here a study of the kinetics of the explosive decomposition of silver azide, initiated by a laser pulse. New effects are identified and studied, including a pre-explosion conductivity and luminescence. On the basis of our results, we conclude that the reaction proceeds by a chain reaction mechanism. In terms of band theory, we propose a model of the primary chain step of the reaction as the creation of a quasilocalized state deep in the valence band with two holes localized at a defect (N₃ ⁰), with impact ionization occurring as they “float up”. State University, Kemerov. Translated from Ivvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 162–175, November, 1996.     

A diffusion model of chain-branching reaction of the explosive decomposition of heavy metal azides

A diffusion model of a solid-phase chain reaction of explosive decomposition of heavy metal azides was developed. The dimensional effects of initiation of the reaction were examined: the dependence of the critical fluence of initiation on the microcrystal size H(R) and on the irradiated zone diameter H(d). It was demonstrated that the diffusion model of the chain reaction closely describes the measured H(R) dependence at diffusion coefficients of D ∼ 0.2–0.3 cm²/s, values that correspond to experimentally measured mobility of electronic charge carriers of μ ∼ 10 cm²/(V s). To account for the measured H(d) dependence and the reaction front propagation velocity (V = 1.2 km/s), it is necessary that the diffusion coefficient be three orders of magnitude higher than the experimentally determined value. That the H(R) and H(d) dependences cannot be quantitatively described simultaneously is indicative of the underlying mechanisms of energy transfer being different.     

Experimental setup for studying the spectral-kinetic and space-dynamic characteristics of explosive decomposition of energetic materials

An experimental setup for studying spectral-kinetic and space-dynamic characteristics of explosion-induced luminescence from energetic materials is described. Explosion is initiated by nanosecond-and picosecond-wide electron and laser beams. Explosive luminescence of a single sample is detected in a spectral interval 450 nm wide with a spectral resolution of 2 nm and a spatial resolution of 50 μm. The time resolution, which is determined by a radiation source, is 30 ps.     

Investigation of early stages of explosive pentaerythritol tetranitrate crystal decomposition initiated by pulsed electron beams

The method of high-resolution pulsed optical spectroscopy is used to investigate the spectral-kinetic characteristics of explosive emission of pentaerythritol tetranitrate crystal excited by a pulsed electron beam (0.25 MeV, 35 ns, and 15 J/cm²). It is established that emission with the spectrum comprising three components with maxima at 3.1, 2.4, and 1.5 eV is initiated in the edge of the excitation pulse. Moreover, transformation of the emission spectrum is observed directly within the time over which the excitation pulse acts followed by the emission decay; however, emission develops again on the subnanosecond scale; moreover, its spectrum contains only the 1.5-eV band, which appears to be an indicator of the self-sustaining chemical reaction of explosive decomposition. The 3.1-and 2.4-eV bands are identified as emissions of an exciton and a primary NO ₂* radiative defect, and the 1.5-eV band is probably connected with the NO ₃ radical. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 3–9, February, 2007.     

Critical parameters of a micro-hotspot model of the laser-pulse initiation of the explosive decomposition of energetic materials

The work continues a series of studies of the micro-hotspot model a thermal explosion. The dependences of the critical energy fluence and the temperature of the reaction kernel in pentaerythritol tetranitrate (PETN) on the radius of aluminum nanoparticles at half-maximum pulse durations of 10 to 150 ns are calculated. For each pulse duration, there is an optimal nanoparticle radius at which the critical energy fluence is minimal. The dependences of these parameters on the pulse duration are derived. It is shown that there is a universal relationship, independent of the pulse duration, between the normalized critical energy fluence and the nanoparticle radius.     

Electronic, chemical and structural characterization of CNTs grown by acetylene decomposition over MgO supported Fe-Co bimetallic catalysts

The electronic and chemical structure of carbon nanotubes synthesized by decomposition of acetylene over Fe-Co bimetallic catalysts in different growth conditions, were analyzed by valence band photoelectron spectroscopy and scanning electron microscopy. A clear relationship between the bonding features and the growth condition allowed us to determine the key parameters in terms of temperature, growth time and catalyst content. Furthermore, the analysis allowed a determination of the byproducts.     

Characteristics of the initiation of the explosive decomposition of PETN by the second-harmonic pulsed radiation of a neodymium laser

The critical fluence of the initiation of the explosive decomposition of pentaerythritol tetranitrate (PETN) by the second harmonic of a neodymium laser (532 nm) is found to be 12.3 J/cm². It is shown that, under these conditions, the nonlinear two-photon absorption of light takes place. The critical fluence of the initiation of PETN explosive decomposition in the two-photon absorption mode is calculated within the framework of the thermal explosion model (14.7 J/cm²), which indicates that the thermal mechanism of explosive decomposition is operative under these conditions.     

Ultrafast dynamics of photoionized acetylene

Acetylene cations [HCCH](+) produced in the A(2)Σ(g)(+) state by extreme ultraviolet (XUV) photoionization are investigated theoretically, based on a mixed quantum-classical approach. We show that the decay of the A(2)Σ(g)(+) state occurs via both ultrafast isomerization and nonradiative electronic relaxation. We find a time scale for hydrogen migration and electronic decay of about 60 fs, in good agreement with recent XUV-pump/XUV-probe time-resolved experiments on the same system [Phys. Rev. Lett. 105, 263002 (2010)]. Moreover, we predict an efficient vibrational energy redistribution mechanism that quickly transfers excess energy from the isomerization coordinates to slower modes in a few hundred femtoseconds, leading to a partial regeneration of acetylenelike conformations.     

Many-wave explosive instability

For special initial phase relations and amplitude values intermediate asymptotic state solutions are obtained to the problem of four interacting triplets of waves yielding explosive instability.     

Anharmonic force field of acetylene

The harmonic and anharmonic force field of acetylene has been determined in a least-squares calculation from recently determined data on the spectroscopic constants of various isotopic species (including the vibrational l-doubling constant). A general quadratic and cubic force field was used, but a constrained quartic force field containing only 8 of the 23 possible quartic constants. The results are discussed and compared with earlier work.     

Pressure of the products of the explosive decomposition of a mixture of pentaerythritol tetranitrate and nickel monocarbide nanoparticles initiated by laser radiation

Relative characteristics of the pressure created by the products of explosive decomposition of a mechanical mixture of pentaerythritol tetranitrate and nickel monocarbide (NiC) nanoparticles upon laser initiation are determined. It is demonstrated that the explosion of the mechanical mixture is caused by the absorption of laser radiation by NiC nanoparticles, a process accompanied by the heating and exothermic decomposition of NiC to the nickel and carbon phases, which, in turn, give rise to the formation of hotspots. The optimal concentration of NiC at which the maximum pressure of the explosion products is achieved is determined.     

Neutrinos and explosive nucleosynthesis

Core-collapse supernovae produce a hot protoneutron star that cools emitting huge amounts of neutrinos of all flavors. The interaction of these neutrinos with the outer layers of the protoneutron star produces an outflow of matter whose composition is determined by the luminosities and energies of the emitted neutrinos and antineutrinos. The presence of light nuclei like deuterons and tritons can have a big impact in the average energies of the emitted antineutrinos and consequently in the neutron-richness of the ejected matter. Recent hydrodynamical models show that the ejected matter is in fact proton-rich and constitutes the site of the νp-process where antineutrino absorption reactions catalyze the nucleosynthesis of nuclei with A>64.     

Simulation of pulsed-laser-induced explosive boiling

Bulk evaporation process in absorbing condensed matter irradiated with laser pulses was studied using the one-dimensional thermal model with additional interfaces between different phases. Within this approach, it was shown that the repeated explosive boiling mode can be achieved using nanosecond laser pulses, if the nucleation time is shorter than 0.1 ns. This mode can be observed if the surface pressure is lower than the critical pressure P _c of the liquid-vapor phase transition. The dependences of these processes on the laser pulse intensity and duration, as well as on evaporation kinetics were studied. Explosive boiling and spallation of a transparent liquid film on a pulse-heated absorbing target, as well as the photoacoustic signal in the target before the explosion, were considered.     

The geometry and forcefield of acetylene

The variational method has been used to determine the geometry and ground state potential surface of acetylene. All the parameters were refined through a least-squares fit to J = 0, 1 levels for C₂H₂ and C₂D₂. A new program was written to evaluate the rovibrational energy levels; in particular, primitive basis sets were developed for all values of J taking into account the singularity for linear geometries. Thus Σ, II, δ states can be refined. The full theory for tetraatomic linear molecules is presented. In this refinement 150 observed levels were used as data, below 10 000cm^?1. The geometry was refined and gives R_e(CC) = 1.2028 Å, R_e(CH) = 1.0618 Å, to be compared with the best experimentally derived values of 1.2027 ± 0.0005 Å, 1.062 ± 0.001 Å, respectively. The zero point energies are 5771.1cm^?1 for C₂H₂ and 4571.1cm^?1 for C₂D₂.     

The acetylene ground state saga

The evolution of high-resolution spectroscopic investigation of the vibration–rotation energy states of acetylene in its ground electronic state is presented, focusing on advances co-authored by the ULB group. The emergence of a global picture accounting for all available spectroscopic fingerprints, at their full accuracy, is highlighted. The contributions of this research to various topics is illustrated, including instrumental developments, local mode trends, quantum vs. classical correspondence, energy vs. time approaches and nucleation processes.     

Interaction between explosive and analyte layers in explosive matrix-assisted plasma desorption mass spectrometry

An HMX/insulin two-layer system was chosen as a model for further investigation of the matrix properties of explosive materials for protein analytes in plasma desorption mass spectrometry. The dependencies of the molecular ion yield and average charge state as a function of the analyte thickness were studied. An increase in the charge state of multiply protonated molecular species was confirmed as the major matrix effect, with the average charge state z at the smallest thickness studied being higher than in matrix-assisted laser desorption/ionization and closer to the value obtained in electrospray ionization under standard acidic conditions. Observed charge state distributions are significantly narrower than the corresponding Poisson distributions, which suggests that the protonation of insulin is limited in plasma desorption by the number of basic sites in the molecule, similar to electrospray ionization. Both the curve displaying total molecular ion yield and the one showing the total charge (proton) yield as a function of the insulin thickness have maxima at a thickness different from an insulin monolayer. These observations diminish the significance of a matrix/analyte interface mechanism for the explosive matrix assistance. Instead, a mechanism related to the chemical energy release during conversion of the explosive after the ion impact is proposed. As additional mechanisms, enhanced protonation of the analyte through collisions with products of the explosive decay is considered, as well as electron scavenging by other products, which leads to a higher survival probability of positively charged protein molecular ions. Copyright 1999 John Wiley & Sons, Ltd.