Onset Of Explosions Research Articles

Effects of dust concentration, particle size, and crude oil concentration on the explosion characteristics of oil-immersed coal dust

To investigate the explosion hazards of oil-immersed coal dust in co-existing mine areas, the explosion characteristic parameters of coal dust under different particle dimensions, coal dust concentration, and oil-immersed concentration were studied in a 20-L explosion chamber. The maximum explosion pressure of oil-immersed coal dust first decreases and then increases as coal dust particle size increases. For oil-immersed concentration samples between 2 and10 wt.%, the Kst value, and maximum explosion pressure of the oil-immersed samples were higher than those of the raw coal counterpart. The maximum explosion pressure of oil-immersed samples was 7.49%, 4.10%, 5.7%, 7.13%, and 4.10% higher than the raw samples. Moreover, when the oil-immersed concentration was 6 wt%, the minimum explosion concentration (MEC) of finer particles was the lowest, while the MEC for large particles was the highest. The impact mechanism of coal dust concentration on maximum explosion pressure is that the number of coal dust particles affects the distance between particles and heat transfer efficiency. The influence mechanism of particle size on the explosion of oil-immersed coal is that the particle size can reflect the specific surface area size, which affects the diffusion of oxygen in particles and the rate of combustible volatiles released by particles. Hydrocarbons released from the crude oil via heating and the complex organic molecules generated during high-temperature pyrolysis produced simpler hydrocarbons, generating hydrogen and higher temperatures that accelerated the onset of explosions and increased coal dust explosion intensity. These experimental results were of use to process safety working and can help prevent coal dust explosion accidents in underground coal mines.

Vulcanian eruption processes inferred from volcanic glow analysis at Sakurajima volcano, Japan

Volcanic glow, which is often observed at active craters during nighttime, contains information on high-temperature zones deep in the crater that are hidden from view. We analyzed 90 eruption videos capturing volcanic glow before the onset of Vulcanian eruptions at the Showa crater of Sakurajima volcano (Japan), and found that they show clear temporal changes. The red (R)-value and the green-to-red ratio (GR ratio) are used to track glow intensity and temperature change, respectively. We found two types of temporal change in glow intensity: a short-term change approximately 1 s before the onset of explosions, and a long-term change 3 to 330 s before an explosion. Short-term changes were observed for 28 of 90 eruptions, and coincided with an increase in the GR ratio and with a modest precursory infrasound pressure increase. Since an increasing GR ratio means a temperature increase, we consider that the change was associated with the opening of tensile cracks on the crater floor before an explosion. However, the other 62 eruptions did not show short-term changes, suggesting that the opening of cracks is sporadic. Long-term changes were observed for 73 of 90 eruptions, the GR ratio did not exhibit a significant increase. We suggest that long-term changes are caused by gradual gas leakage, which precedes initiation of Vulcanian eruptions. We hypothesize that the long-term gas leakage causes gradual decompression of the conduit, which induces supersaturation of volatile-rich magma beneath the lava plug causing explosive expansion, thereby triggering an eruption.

The Impact of Agroecological Practices on the Biodiversity of Arthropod Fauna in Târnave Vineyard


 In viticultural ecosystems, considered energy-intensive systems, the amplification of biocoenotic imbalances with the onset of pest explosions, is a problem and also an evidence of the biodiversity’s decline. In this study the biodiversity was quantified in Târnave vineyard, in the period 2016-2018, in the experimental plots of SCDVV Blaj cultivated with the Fetească regală cultivar, for two cultivation technologies, the extensive agroecological (EA) and the intensive conventional (IC). The determined biodiversity characterization indicators were: the species richness, Simpson biodiversity index (D), Shanon biodiversity index (H) and Equity index (E). In case of the Heteroptera group EA technology doubled the number of the arthropods (11.333 ± 0.882 for EA versus 5.33 ± 1.453 for IC). The reverse effect was observed for Coleoptera were in the case of EA it was found a taxa richness of 8.667 ± 0.882 and for IC one of 15.667 ± 1.764. Considering the increase of the number of useful species from the order Heteroptera in the agroecological variant compared to the conventional variant, we consider that the implementation of the agroecological technology for a longer period (5-10 years) can be a long-term solution that will contribute to reducing the risk induced by the intensive practices, while reducing the dependence of culture on conventional energy resources.

Seismo-acoustic characterisation of the 2018 Ambae (Manaro Voui) eruption, Vanuatu

A new episode of unrest and phreatic/phreatomagmatic/magmatic eruptions occurred at Ambae volcano, Vanuatu, in 2017–2018. We installed a multi-station seismo-acoustic network consisting of seven 3-component broadband seismic stations and four 3-element (26–62 m maximum inter-element separation) infrasound arrays during the last phase of the 2018 eruption episode, capturing at least six reported major explosions towards the end of the eruption episode. The observed volcanic seismic signals are generally in the passband 0.5–10 Hz during the eruptive activity, but the corresponding acoustic signals have relatively low frequencies (< 1 Hz). Apparent very-long-period (< 0.2 Hz) seismic signals are also observed during the eruptive episode, but we show that they are generated as ground-coupled airwaves and propagate with atmospheric acoustic velocity. We observe strongly coherent infrasound waves at all acoustic arrays during the eruptions. Using waveform similarity of the acoustic signals, we detect previously unreported volcanic explosions at the summit vent region based on constant-celerity reverse-time-migration (RTM) analysis. The detected acoustic bursts are temporally related to shallow seismic volcanic tremor (frequency content of 5–10 Hz), which we characterise using a simplified amplitude ratio method at a seismic station pair with different distances from the vent. The amplitude ratio increased at the onset of large explosions and then decreased, which is interpreted as the seismic source ascent and descent. The ratio change is potentially useful to recognise volcanic unrest using only two seismic stations quickly. This study reiterates the value of joint seismo-acoustic data for improving interpretation of volcanic activity and reducing ambiguity in geophysical monitoring.

Analysis of the final stage of flame acceleration and the onset of detonation in a cylindrical tube using high-speed stereoscopic imaging

The three-dimensional structure of an accelerating flame front makes it very difficult to visualize. Most experimental studies that provided a visualization of flame acceleration and deflagration-to-detonation transition (DDT) events were done in rectangular tubes using the shadow technique. Qualitative information obtained by these optical methods has been two-dimensional and line-of-sight integrated, so local peculiarities and trends of the phenomena may not be spatially resolved in the third dimension. Here, we present a high-speed imaging analysis (self-luminous stereoscopic photography) of the final stage of fast flame propagation, the formation of new autoignition kernels and the onset of localized explosions in a long smooth transparent cylindrical tube. We investigated the evolution of the accelerating flame shape along the tube and found that before transition to detonation the flame shape is quite stable and looks like a “paper cone” or “waffle cone”, instead of the usual shape that is referred to as a “tulip flame”. Simultaneous images captured by two high-speed cameras positioned 90° apart allowed us to determine the location of the auto-ignition kernels and the explosion points in reaction gas volume behind the leading shock wave. Both the horizontal position with respect to the leading edge of the flame and the position across the tube cross-section were determined. We observed the four typical scenarios for the onset of detonation in front of the accelerating flame where explosion occurs in the boundary layer to be: (1) between the secondary reaction fronts that emerge from the auto-ignition kernels; (2) between the main flame front and the secondary reaction fronts that emerge from the auto-ignition kernels; (3) at the leading tip of the secondary reaction fronts; (4) at the tip of the main turbulent flame front. We determined the local gas parameters between the flame front and the leading shock wave directly before the onset of detonation. The flow stagnation in the boundary layer near the tube wall leads to a significant local temperature increase and strongly reduces the ignition delay time of the mixture. Simple kinetic calculations show that for our test conditions, a temperature rise of approximately 275 K results in an induction time reduction by 15 times.

Integrated constraints on explosive eruption intensification at Santiaguito dome complex, Guatemala

Protracted volcanic eruptions may exhibit unanticipated intensifications in explosive behaviour and attendant hazards. Santiaguito dome complex, Guatemala, has been characterised by century-long effusion interspersed with frequent, small-to-moderate (<2 km high plumes) gas-and-ash explosions. During 2015–2016, explosions intensified generating hazardous ash-rich plumes (up to 7 km high) and pyroclastic flows. Here, we integrate petrological, geochemical and geophysical evidence to evaluate the causes of explosion intensification. Seismic and infrasound signals reveal progressively longer repose intervals between explosions and deeper fragmentation levels as the seismic energy of these events increased by up to four orders of magnitude. Evidence from geothermobarometry, bulk geochemistry and groundmass microlite textures reveal that the onset of large explosions was concordant with a relatively fast ascent of a deeper-sourced (∼17–24 km), higher temperature (∼960–1020°C) and relatively volatile-rich magma compared to the previous erupted lavas, which stalled at ∼2 km depth and mingled with the left-over mush that resided beneath the pre-2015 lava dome. We interpret that purging driven by the injection of this deep-sourced magma disrupted the long-term activity, driving a transition from low energy shallow shear-driven fragmentation, to high energy deeper overpressure-driven fragmentation that excavated significant portions of the conduit and intensified local volcanic hazards. Our findings demonstrate the value of multi-parametric approaches for understanding volcanic processes and the triggers for enigmatic shifts in eruption style, with the detection of vicissitudes in both monitoring signals and petrological signatures of the eruptive products proving paramount.

Impact of high-order effects on soliton explosions in the complex cubic-quintic Ginzburg-Landau equation

We investigate the impact of higher-order nonlinear and dispersive effects on the onset of soliton explosions in the complex cubic-quintic Ginzburg-Landau equation. We show how the interplay of the high order effects (HOEs) results in the splitting of symmetric explosion modes and to the formation of right- or left-side periodic explosions. In addition, we demonstrate that HOEs induce a series of pulsating instabilities, leading to a significant reduction of the stability region of the single soliton solution.

The non-linear onset of neutrino-driven convection in two- and three-dimensional core-collapse supernovae

A toy model of the post-shock region of core-collapse supernovae is used to study the non-linear development of turbulent motions driven by convection in the presence of advection. Our numerical simulations indicate that buoyant perturbations of density are able to trigger self-sustained convection only when the instability is not linearly stabilized by advection. Large amplitude perturbations produced by strong shock oscillations or combustion inhomogeneities before the collapse of the progenitor are efficiently shredded through phase mixing and generate a turbulent cascade. Our model enables us to investigate several physical arguments that had been proposed to explain the impact of the dimensionality on the onset of explosions in global simulations of core-collapse supernovae. Three-dimensional (3D) simulations are found to lead to higher entropy values than two-dimensional (2D) ones. We attribute this to greater turbulent mixing and dissipation of the kinetic energy into heat in 3D. Our results show that the increase of entropy is enhanced with finer numerical resolution and larger perturbation amplitude.

Impact of Lyman alpha pressure on metal-poor dwarf galaxies

AbstractUnderstanding the origin of strong galactic outflows and the suppression of star formation in dwarf galaxies is a key problem in galaxy formation. Using a set of radiation-hydrodynamic simulations of an isolated dwarf galaxy embedded in a 1010 M⊙ halo, we show that the momentum transferred from resonantly scattered Lyman-α (Lyα) photons is an important source of stellar feedback which can shape the evolution of galaxies. We find that Lyα feedback suppresses star formation by a factor of two in metal-poor galaxies by regulating the dynamics of star-forming clouds before the onset of supernova explosions (SNe). This is possible because each Lyα photon resonantly scatters and imparts ∼10–300 times greater momentum than in the single scattering limit. Consequently, the number of star clusters predicted in the simulations is reduced by a factor of ∼5, compared to the model without the early feedback. More importantly, we find that galactic outflows become weaker in the presence of strong Lyα radiation feedback, as star formation and associated SNe become less bursty. We also examine a model in which radiation field is arbitrarily enhanced by a factor of up to 10, and reach the same conclusion. The typical mass-loading factors in our metal-poor dwarf system are estimated to be ∼5–10 near the mid-plane, while it is reduced to ∼1 at larger radii. Finally, we find that the escape of ionizing radiation and hence the reionization history of the Universe is unlikely to be strongly affected by Lyα feedback.

The Farahat sodium natural convection film boiling experiment revisited

With the renewal of interest for sodium-cooled fast reactors, looking at what is known from the past, it appears – in the frame of severe accident studies in general and FCI in particular, that very few is known about sodium film boiling around hot fuel droplets which is a condition allowing premixing. The past Farahat experiment (Reynolds et al., 1976), performed in 1971, in which hot solid spheres were transferred into sodium has been revisited. Looking in the detailed results, it appears that a phenomena has been ignored, i.e. the existence of two film boiling regimes as observed in similar experiments with water (Honda et al., 1995; Bradfield, 1966). These two film boiling regimes have been analyzed since the transition between these regimes could lead to the onset of spontaneous explosions if the melt is still liquid at this transition. A simple model has been built for the estimation of this transition point. As this model is able to describe the transition observed in Sn-H2O experiments (Sher, 2012), it has been used for UO2-Na systems.

Continuous measurements of SiF4 and SO2 by thermal emission spectroscopy: Insight from a 6-month survey at the Popocatépetl volcano

The processes linked with the emplacement and growth/destruction of a lava dome are of prime importance to understand the stability of such extrusions and assess the associated risks for local populations. During the last couple of decades, ground and space-based spectroscopic techniques have been developed to monitor such processes from a safe distance. Such approaches significantly improved our knowledge about the relationship between the chemical composition of the volcanic gas plumes and both the deep and shallow volcanic processes leading to the different types of explosive activity. The potential of the ground-based thermal emission Fourier Transform Infrared spectroscopy (FTIR) remained under-exploited due to the difficulty to properly handle the radiative-transfer phenomena. Despite the drawbacks in the complex analytical requirements, this method enables to continuously monitor (day and night) with a high temporal resolution (1meas/3min), relevant gas species such as SO2 and SiF4 in the volcanic plumes. Previous studies have related the temporal variations of the SiF4/SO2 ratio in volcanic plumes to the onset of vulcanian explosions. This study reports a 6-month SO2, SiF4, and SiF4/SO2 time series (from January to June 2015) of the Popocatepetl's gas plume obtained from FTIR thermal emission spectroscopic measurements. The infrared spectra were analyzed using the SFIT4 radiative transfer and inverse model, which we have adapted for this application. We obtained highly variable SiF4/SO2 ratios with a mean value of 3.6×10−4, with the highest values (around 3×10−3) measured during the final phase of a lava dome growth (February–March 2015). The rapid SiF4/SO2 variations were more carefully explored and compared for the first time with the seismic activity. A remarkable coincidence between sharp SiF4/SO2 rises and the seismic events are evidenced here.

THREE-DIMENSIONAL SIMULATION OF A ROTATING CORE-COLLAPSE SUPERNOVA

Multi-dimensionality in the inner working of core-collapse supernovae has long been considered one of the most important ingredients to understand the explosion mechanism. We perform a series of numerical experiments to explore how rotation impacts the 3-dimensional hydrodynamics of core-collapse supernova. We employ a light-bulb scheme to trigger explosions and a three-species neutrino leakage scheme to treat deleptonization eects and neutrino losses from the neutron star interior. We nd that the rotation can help the onset of neutrino-driven explosions for models in which the initial angular momentum is matched to that obtained from recent stellar evolutionary calculations ( 0:3 - 3 rad s 1 at the center). For models with larger initial angular momenta, a shock surface deforms to be oblate due to larger centrifugal force. This makes a gain region, in which matter gains energy from neutrinos, more concentrated around the equatorial plane. As a result, the preferred direction of the explosion in 3-dimensional rotating models is perpendicular to the spin axis, which is in sharp contrast to the polar explosions around the axis that are often obtained from 2-dimensional simulations.

IMPACTS OF ROTATION ON THREE-DIMENSIONAL HYDRODYNAMICS OF CORE-COLLAPSE SUPERNOVAE

We perform a series of simplified numerical experiments to explore how rotation impacts on the three-dimensional (3D) hydrodynamics of core-collapse supernovae. For the sake of our systematic study, we employ a light-bulb scheme to trigger explosions and a three-flavor neutrino leakage scheme to treat deleptonization effects and neutrino losses from proto-neutron star interior. Using a 15 solar mass progenitor, we compute thirty models in 3D with a wide variety of initial angular momentum and light-bulb neutrino luminosity. We find that the rotation can help onset of neutrino-driven explosions for the models in which the initial angular momentum is matched to that obtained in recent stellar evolutionary calculations (0.3-3 rad/s at the center). For the models with larger initial angular momentum, the shock surface deforms to be more oblate due to larger centrifugal force. This makes not only a gain region more concentrated around the equatorial plane, but also the mass in the gain region bigger. As a result, buoyant bubbles tend to be coherently formed and rise in the equatorial region, which pushes the revived shock ever larger radii until a global explosion is triggered. We find that these are the main reasons that the preferred direction of explosion in 3D rotating models is often perpendicular to the spin axis, which is in sharp contrast to the polar explosions around the axis that was obtained in previous 2D simulations.

REVISITING IMPACTS OF NUCLEAR BURNING FOR REVIVING WEAK SHOCKS IN NEUTRINO-DRIVEN SUPERNOVAE

We revisit potential impacts of nuclear burning on the onset of the neutrino-driven explosions of core-collapse supernovae. By changing the neutrino luminosity and its decay time to obtain parametric explosions in one-(1D) and two-dimensional (2D) models with or without a 13-isotope alpha network, we study how the inclusion of nuclear burning could affect the postbounce dynamics for four progenitor models; three for 15.0 Msun stars, one for an 11.2 Msun star. We find that the energy supply due to nuclear burning of infalling material behind the shock can energize the shock expansion especially for models that produce only marginal explosions in the absence of nuclear burning. These models are energized by nuclear energy deposition when the shock front passes through the silicon-rich layer and/or later it touches the oxygen-rich layer. Depending on the neutrino luminosity and its decay time, a diagnostic energy of explosion increases up to a few times 10^50 erg for models with nuclear burning compared to the corresponding models without. We point out that these features are most remarkable for the Limongi-Chieffi progenitor in both 1D and 2D, because the progenitor model possesses a massive oxygen layer with its inner-edge radius being smallest among the employed progenitors, so that the shock can touch the rich fuel on a shorter timescale after bounce. The energy difference is generally smaller (~0.1-0.2 times 10^51 erg) in 2D than in 1D (at most ~0.6 times 10^51 erg). This is because neutrino-driven convection and the shock instability in 2D models enhance the neutrino heating efficiency, which makes the contribution of nuclear burning relatively smaller compared to 1D models. Considering uncertainties in progenitor models, our results indicate that nuclear burning should remain as one of the important ingredients to foster the onset of neutrino-driven explosions.

Intermittent explosions of dissipative solitons and noise-induced crisis

Dissipative solitons show a variety of behaviors not exhibited by their conservative counterparts. For instance, a dissipative soliton can remain localized for a long period of time without major profile changes, then grow and become broader for a short time-explode-and return to the original spatial profile afterward. Here we consider the dynamics of dissipative solitons and the onset of explosions in detail. By using the one-dimensional complex Ginzburg-Landau model and adjusting a single parameter, we show how the appearance of explosions has the general signatures of intermittency: the periods of time between explosions are irregular even in the absence of noise, but their mean value is related to the distance to criticality by a power law. We conjecture that these explosions are a manifestation of attractor-merging crises, as the continuum of localized solitons induced by translation symmetry becomes connected by short-lived trajectories, forming a delocalized attractor. As additive noise is added, the extended system shows the same scaling found by low-dimensional systems exhibiting crises [J. Sommerer, E. Ott, and C. Grebogi, Phys. Rev. A 43, 1754 (1991)], thus supporting the validity of the proposed picture.

ON THE IMPORTANCE OF THE EQUATION OF STATE FOR THE NEUTRINO-DRIVEN SUPERNOVA EXPLOSION MECHANISM

By implementing widely-used equations of state (EOS) from Lattimer & Swesty (LS) and H. Shen et al. (SHEN) in core-collapse supernova simulations, we explore possible impacts of these EOS on the post-bounce dynamics prior to the onset of neutrino-driven explosions. Our spherically symmetric (1D) and axially symmetric (2D) models are based on neutrino radiation hydrodynamics including spectral transport, which is solved by the isotropic diffusion source approximation. We confirm that in 1D simulations neutrino-driven explosions cannot be obtained for any of the employed EOS. Impacts of the EOS on the post-bounce hydrodynamics are more clearly visible in 2D simulations. In 2D models of a 15 M_sun progenitor using the LS EOS, the stalled bounce shock expands to increasingly larger radii, which is not the case using the SHEN EOS. Keeping in mind that the omission of the energy drain by heavy-lepton neutrinos in the present scheme could facilitate explosions, we find that 2D models of an 11.2 M_sun progenitor produce neutrino-driven explosions for all the EOS under investigation. Models using the LS EOS are slightly more energetic compared to those with the SHEN EOS. The more efficient neutrino heating in the LS models coincides with a higher electron antineutrino luminosity and a larger mass that is enclosed within the gain region. The models based on the LS EOS also show a more vigorous and aspherical downflow of accreting matter to the surface of the protoneutron star (PNS). The accretion pattern is essential for the production and strength of outgoing pressure waves, that can push in turn the shock to larger radii and provide more favorable conditions for the explosion. [abbreviated]

Cutting-edge issues in core-collapse supernova theory

AbstractBased on our multi-dimensional neutrino-radiation hydrodynamic simulations, we report several cutting-edge issues about the long-veiled explosion mechanism of core-collapse supernovae (CCSNe). In this contribution, we pay particular attention to whether three-dimensional (3D) hydrodynamics and/or general relativity (GR) would or would not help the onset of explosions. Our results from the first generation of full GR 3D simulations including approximate neutrino transport are quite optimistic, indicating that both of the two ingredients can foster neutrino-driven explosions. We give an outlook with a summary of the most urgent tasks to draw a robust conclusion to our findings.

Probing Stromboli volcano from the mantle to paroxysmal eruptions

Abstract We investigated the plumbing system of Stromboli volcano from the upper mantle to the surface. Thermobarometric estimates indicate that the deeper detected part of the plumbing system is located in the upper mantle, at approximately 34–24 km depth where, during their ascent, primitive Stromboli basalts (HKCA to shoshonitic) interact with peridotitic materials. In this region magma flow is probably channelled along fracture zones that may converge into a feeder dyke that crosscuts the Moho at about 17 km depth. During their ascent, basaltic magmas will interact with lower crust materials represented by cumulates of earlier Stromboli-type basalts at 13–10 km depth. This zone is also the section of the plumbing system where the feeder dyke is entering the chamber. Thermobarometric estimates, obtained by constructing a grid of selected reactions, indicate that current primitive Stromboli basalts equilibrate at 0.3–0.15 GPa and temperatures approaching 1200 °C, and progressively crystallize and degas before being erupted. Crystal size distributions on lavas and juvenile tephra erupted in 2002–2003 give very variable residence times. Based on average bubble distances, the estimated times for the exsolution of the gaseous phases range from 2–7 days to 45 min for the lavas and scorias, down to about 15 h to 12 min for the pumices erupted during paroxysmal explosions. Estimated syneruptive viscosities range from 10 2 Pa s for the anhydrous basaltic pumices at 1200 °C, to 10 3 –10 4 Pa s for lavas approaching their effusion temperatures (1100–1150 °C). In turn, viscosities for the hydrous basaltic melt that led to the formation of the basaltic pumices may be around 10 Pa s or lower. In the light of the above, we discuss the possible shapes and volumes of Stromboli magma chamber by considering a sphere, an ellipsoid (geometrically concordant with the regional stress distribution) and a feeder dyke, the last two being more likely. In the light of volcanological, structural and geophysical data on conduit thickness, we propose an alternative model that takes into account the volumes of recently erupted lavas. This model consists of a convective ellipsoidal magma chamber ‘injected’ by an active feeder dike of undegassed magma of higher temperature, lower density and lower viscosity. This dyke will evolve into a magma column inside the chamber and will separate the reservoir into two lateral, nearly symmetric convective regions. Crystallization would occur preferentially in the proximity of the wallrocks, particularly where the chamber is entering the conduit. The onset of paroxysmal explosions during major effusive cycles may be explained by a drastic increase in the intrusion rates at the base of the chamber that will produce a progressive inflation of the magma column dynamically transferred to the chamber walls. The ceasing of ‘anomalous’ intrusion rates at the base of the chamber, coupled with higher discharge rates, will progressively depressurize the chamber to a critical threshold, until the stress transferred to the walls is dynamically released: at this point the walls themselves will undergo a nearly instantaneous elastic rebound and contract in the attempt to recover their original pre-eruptive geometry. These dynamics will squeeze up portions of the undegassed magma column, triggering a paroxysmal explosion with the ejection of ‘golden pumices’.

Ionization and Fragmentation of Some Chlorinated Compounds and Dibenzo-p-dioxin with an Intense Femtosecond Laser Pulse at 800 nm

We detected parent and fragment ions from 14 chlorinated and a few fluorinated compounds as well as dibenzo-p-dioxin (dioxin) in intense laser fields. The irradiation pulse had an intensity from 1 × 1013 to 1 × 1015 W cm-2, with a 130-fs pulse duration at a central wavelength of 800 nm. Irradiation at this intensity led to a singly ionized species and a small amount of atomic ions, indicating the onset of Coulomb explosions. We have previously reported finding a key factor in determining the parent and/or fragment ion formations of organic hydrocarbons with an intense femtosecond laser pulse [Harada, H.; et al. Chem. Phys. Lett. 2001, 342, 563−570]. This key factor is a requirement for parent ion predominance if the excitation laser wavelength and the absorption spectra of the target cation are in nonresonance, and vice versa. Use of this factor has been found to be effective for molecules other than hexachlorobutadiene. The threshold intensities Isat at the infinity ionization rate were determined and ar...

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.