Mechanism of Intact Adsorbed Molecules Ejection Using High Intensity Laser Pulses

A novel universal mechanism for the ejection of intact, neutral molecules from thin films into the gas phase initiated by high intensity ultrashort laser pulses is described. The proposed mechanism is substantiated by detailed reactive molecular dynamics simulations. In the present study, 2,4,6-trinitrotoluene (TNT) and cryogenic benzene are used as thin film targets. According to the proposed mechanism, the laser pulse, absorbed by the substrate, forms a hot plasma plume which in turn generates a shock wave that moves across the deposited thin film. The simulations indicate that the shock wave propagates through the thin film without dissipation and eventually ejects molecules from the free surface. It is revealed that the proposed mechanism is feasible only in a limited range of shock velocities. The results compare well qualitatively with recent experimental findings of femtosecond, nonresonant, laser-induced desorption. Simple experimental measurements are outlined to validate the proposed mechanism

Enhanced Particle Swarm Optimization Algorithm: Efficient Training of ReaxFF Reactive Force Fields

Particle swarm optimization (PSO) is a powerful metaheuristic population-based global optimization algorithm. However, when it is applied to nonseparable objective functions, its performance on multimodal landscapes is significantly degraded. Here we show that a significant improvement in the search quality and efficiency on multimodal functions can be achieved by enhancing the basic rotation-invariant PSO algorithm with isotropic Gaussian mutation operators. The new algorithm demonstrates superior performance across several nonlinear, multimodal benchmark functions compared with the rotation-invariant PSO algorithm and the well-established simulated annealing and sequential one-parameter parabolic interpolation methods. A search for the optimal set of parameters for the dispersion interaction model in the ReaxFF-<i>l</i>g reactive force field was carried out with respect to accurate DFT-TS calculations. The resulting optimized force field accurately describes the equations of state of several high-energy molecular crystals where such interactions are of crucial importance. The improved algorithm also presents better performance compared to a genetic algorithm optimization method in the optimization of the parameters of a ReaxFF-<i>l</i>g correction model. The computational framework is implemented in a stand-alone C++ code that allows the straightforward development of ReaxFF reactive force fields

MOESM4 of Spontaneous penetration of gold nanoparticles through the blood brain barrier (BBB)

Additional file 4. Instrument optimization. Tables S1 and S2 summarize the optimal operational parameters for the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Laser Ablation-ICP-MS systems used in the present work

MOESM2 of Spontaneous penetration of gold nanoparticles through the blood brain barrier (BBB)

Additional file 2. LA-ICP-MS 2D imaging of gold distribution in the hippocampus and the hypothalamus. Figure S1 present LA-ICP-MS 2D imaging of gold distribution in the hippocampus and the hypothalamus, as representative regions of brain

Reactive Force Field for Liquid Hydrazoic Acid with Applications to Detonation Chemistry

The development of a reactive force field (ReaxFF formalism) for hydrazoic acid (HN₃), a highly sensitive liquid energetic material, is reported. The force field accurately reproduces results of density functional theory (DFT) calculations. The quality and performance of the force field are examined by detailed comparison with DFT calculations related to uni, bi, and trimolecular thermal decomposition routes. Reactive molecular dynamics (RMD) simulations are performed to reveal the initial chemical events governing the detonation chemistry of liquid HN₃. The outcome of these simulations compares very well with recent results of tight-binding DFT molecular dynamics and thermodynamic calculations. On the basis of our RMD simulations, predictions were made for the activation energies and volumes in a broad range of temperatures and initial material compressions

First-Principles-Based Reaction Kinetics for Decomposition of Hot, Dense Liquid TNT from ReaxFF Multiscale Reactive Dynamics Simulations

The reaction kinetics of the thermal decomposition of hot, dense liquid TNT was studied from first-principles-based ReaxFF multiscale reactive dynamics simulation strategy. The decomposition process was followed starting from the initial liquid phase, decomposition to radicals, continuing through formation of carbon-clusters products, and finally to formation of the stable gaseous products. The activation energy of the initial endothermic decomposition rate and the subsequent exothermic reactions were determined as a function of density. Analysis of fragments production in different densities and temperatures is presented. We find that unimolecular C–N bond scission dominates at the lower densities (producing NO₂), whereas dimer formation and decomposition to TNT derivatives and smaller gaseous fragments prevails at higher compressions. At higher densities, enhanced carbon-clustering is observed, while the initial gaseous fragments formation is suppressed. Increasing the temperature speeds up the production of both clusters and gaseous products. The activation energy for the initial decomposition stage of ambient liquid TNT is ∼36 kcal/mol, close to the measured value (∼40 kcal/mol). This value is ∼25 kcal/mol lower than the corresponding gas phase C–N bond scission. Finally, we suggest a simple linear growth kinetic model for describing the clustering process, which provides very good agreement with simulation results

Thermal Decomposition of Erythritol Tetranitrate: A Joint Experimental and Computational Study

Pentaerythritol tetranitrate (PETN) finds many uses in the energetic materials community. Due to the recent availability of erythritol, erythritol tetranitrate (ETN) can now be readily synthesized. Accordingly, its complete characterization, especially its stability, is of great interest. This work examines the thermal decomposition of ETN, both through experimental and computational methods. In addition to kinetic parameters, decomposition products were examined to elucidate its decomposition pathway. It is found that ETN begins its decomposition sequence by a unimolecular homolytic cleavage of the internal and external O–NO₂ bonds, while the competing HONO elimination reaction is largely suppressed. The global activation energy for decomposition is found to be 104.3 kJ/mol with a pre-exponential factor of 3.72 × 10⁹ s^–1. Despite the ability to exist in a molten state, ETN has a lower thermal stability than its counterpart PETN