Internal Energy Distribution Research Articles

Dynamics of the isotope exchange reaction of D with H3 +, H2D+, and D2H.

We have measured the merged-beams rate coefficient for the titular isotope exchange reactions as a function of the relative collision energy in the range of ∼3 meV-10 eV. The results appear to scale with the number of available sites for deuteration. We have performed extensive theoretical calculations to characterize the zero-point energy corrected reaction path. Vibrationally adiabatic minimum energy paths were obtained using a combination of unrestricted quadratic configuration interaction of single and double excitations and internally contracted multireference configuration interaction calculations. The resulting barrier height, ranging from 68 meV to 89 meV, together with the various asymptotes that may be reached in the collision, was used in a classical over-the-barrier model. All competing endoergic reaction channels were taken into account using a flux reduction factor. This model reproduces all three experimental sets quite satisfactorily. In order to generate thermal rate coefficients down to 10 K, the internal excitation energy distribution of each H3 + isotopologue is evaluated level by level using available line lists and accurate spectroscopic parameters. Tunneling is accounted for by a direct inclusion of the exact quantum tunneling probability in the evaluation of the cross section. We derive a thermal rate coefficient of <1×10-12 cm3 s-1 for temperatures below 44 K, 86 K, and 139 K for the reaction of D with H3 +, H2D+, and D2H+, respectively, with tunneling effects included. The derived thermal rate coefficients exceed the ring polymer molecular dynamics prediction of Bulut et al. [J. Phys. Chem. A 123, 8766 (2019)] at all temperatures.

Ligand effects in gold-carbonyl complexes: Evaluation of the bond dissociation energies using blackbody infrared radiative dissociation

In a previous work, the ability of gold-carbonyl bond dissociation energies (BDEs) to describe ligand effects in gold(I) complexes was probed using collision-induced dissociation measurements. Despite the large experimental error of the technique, results agreed with theoretical description of these effects. We propose here another experimental approach to evaluate the BDEs of [LAu-CO]+ complexes, by using Blackbody Infrared Radiative Dissociation (BIRD) method which is able to provide absolute energetic measurements. To this aim, the dissociation of 8 gold-carbonyl complexes was studied with this approach to obtain their Arrhenius activation energies. Because these complexes do not reach the rapid energy exchange (REX) limit conditions, critical energies of these dissociations were then determined using the kinetic data and an Equilibrium Truncated Thermal (ETT) internal energy distribution model implemented in the RRKM-QET MassKinetics software. To validate our approach, the known critical energies of proton-bound amino acid dimers were first reinvestigated using this model. The results are in excellent agreement with those reported in the literature. This indicates that the assumptions of this simple model are reasonable and allow the determination of accurate dissociation energies. For [LAu-CO]+ complexes, even though a shift (from 0.18 to 0.26 eV) is observed between binding energies obtained and calculated values, a linear tendency between these two sets of data is still obtained. These results validate the use of BIRD in combination with equilibrium truncated thermal internal energy distributions model to obtain dissociation energies for relatively small ions. It is also shown herein that the measure of the gold-carbonyl bond dissociation energies is a good descriptor of ligand effects in gold(I) complexes that may be reliably evaluated using the BIRD technique.

Advanced techniques for quantum-state specific reaction dynamics of gas phase metal atoms

One of the themes of modern molecular reaction dynamics is to characterize elementary chemical reactions from “quantum state to quantum state”, and the study of molecular reaction dynamics in excited states can help test the validity of modern chemical theories and provide methods to control chemical reactions. The subject of this review is to describe the recent experimental techniques used to study the reaction dynamics of metal atoms in the gas phase. Through these techniques, information such as the internal energy distribution and angular distribution of the nascent products or the three-dimensional stereodynamic reactivity can be obtained. In addition, by preparing metal atoms with specific excited electronic states or orbital arrangements, information about the reactivity of the electronic states enriches the relevant understanding of the electron transfer mechanism in metal reaction dynamics.

Seismic performance and effective isolation of a large multilayered underground subway station

In this paper, the seismic performance of a reinforced concrete (RC)-framed underground subway station structure which has three stories and three spans was analyzed firstly under strong earthquakes. It was found that the central columns in the top and the bottom stories were the weakest seismic components in this type of underground structure. Thus, lead-core rubber bearings (LRBs) were installed at the central column-tops of the structure, and the seismic performance of the underground station structure with LRBs was also studied. The results show that LRBs can reduce the seismic damage to the central columns and interior slabs and the lateral deformation of the central columns effectively. While the installation of LRBs will also change the internal force transfer characteristics and energy distribution of the large underground structure and increase the seismic damage to the top and bottom slabs and side walls to some extent. In particular, when LRBs were only set on the central column-tops in the top and bottom stories, which have the most unfavorable seismic performance in the underground structure, the seismic damage to the central columns without LRBs was significantly exacerbated. The isolation method of installing LRBs at the top of the central columns in each story was clearly superior and could ensure that the underground station structure would not collapse due to serious damage of the columns under strong earthquakes.

Comparison of internal energy distributions generated by supercritical fluid chromatography versus liquid chromatography hyphenated with electrospray high resolution mass spectrometry

The internal energy distributions of thermometer ions dissolved in supercritical and liquid solvents and produced in the gas phase by electrospray (ESI) were measured and compared by the survival yield method. The influence of different chromatographic conditions such as the nature of solvents, the composition of the mobile phase, the pressure of the back pressure regulator was studied for supercritical fluid chromatography (SFC) whereas the influence of the composition and of the flow rate of the mobile phase was investigated for liquid chromatography (LC). The MS instrumental parameters were studied in parallel for SFC and LC showing that the drying gas temperature and the fragmentor voltage affected the internal energy distribution, whereas the capillary voltage did not modify the internal energy distribution. A comparison of the internal energy distributions generated by SFC and LC was carried out leading to conclude that SFC led to higher internal energy, i.e. more in-source fragment ions, than LC.

Production of PAH cations with narrow internal energy distribution using single nanosecond pulsed laser

The internal energy dynamics of three examples of PAHs are probed using a high resolution energy time of flight spectrometer. The measured H-loss rates are converted to internal energy values for a range of UV photon wavelengths. Multi step multi photon absorption scheme is proposed to estimate the possible internal energy values with reasonable accuracies. This was possible because of the ultrafast radiationless internal conversion process in PAHs and their structural rigidity. Thus, a method is proposed to produce PAH cations with narrow and known internal energy distribution using a single nanosecond pulsed laser, paving a way to study statistical unimolecular decay in PAHs very efficiently.

Fluctuations and Correlations of Transmission Eigenchannels in Diffusive Media.

Selective excitation of a diffusive system's transmission eigenchannels enables manipulation of its internal energy distribution. The fluctuations and correlations of the eigenchannel's spatial profiles, however, remain unexplored so far. Here we show that the depth profiles of high-transmission eigenchannels exhibit low realization-to-realization fluctuations. Furthermore, our experimental and numerical studies reveal the existence of interchannel correlations, which are significant for low-transmission eigenchannels. Because high-transmission eigenchannels are robust and independent from other eigenchannels, they can reliably deliver energy deep inside turbid media.

Cis-trans isomerization is not rate determining for b2 ion structures: A guided ion beam and computational study of the decomposition of H+(GlyProAla)

Decomposition of the protonated tripeptide, GlyProAla (H+GPA), through collision-induced dissociation with Xe in a guided ion beam tandem mass spectrometer (GIBMS) is examined. Cross sections for the formation of [b2]+, [y2 + 2H]+, [a1]+, [b3]+, [a3]+, [a2]+, and H+(1-pyrroline) fragment ions were collected as a function of kinetic energy. Analysis of these cross sections include consideration of the effects of multiple collisions, dissociation lifetimes, reactant internal and kinetic energy distributions, competition among channels, and evolution into sequential channels. Structures and molecular parameters of reactants, transition states, intermediates, and products were identified using the B3LYP/6-311+G(d,p) level of theory, with single-point energy calculations performed at the B3LYP, B3P86, and MP2(full) levels of theory using a 6-311+G(2d,2p) basis set. Good agreement between experimental threshold energies and those calculated for rate-limiting transition states allow key reaction pathways for the formation of each product to be identified. The MP2(full) level of theory is found to agree best with the experimental results. Notably, even though H+GPA starts with a cis-peptide bond, it forms an oxazolone as its [b2]+ fragment and the absence of a diketopiperazine [b2]+ fragment is verified by other key observations.

Final-State-Resolved Dynamics of the H3+ + CO → H2 +HCO+/HOC+ Reaction: A Quasi-Classical Trajectory Study.

The ion-molecule reaction H3+ + CO → H2 + HCO+/HOC+, which initiates the formation of crucial organic molecules, plays a key role in interstellar and circumstellar environments. In this work, the quasi-classical trajectory method is employed to study the reaction dynamics on a recently developed full-dimensional global potential energy surface (PES). The calculated product internal energy distributions and relative internal excited fractions agree reasonably well with the experimental measurements. For the two reaction channels, most of the available energy flows into the vibrational modes of HCO+ or HOC+ at low collision energies, followed by the translational mode and the rotational modes of HCO+ or HOC+. As the collision energy increases, the proportion of the product translational energy increases while the proportion of the product vibrational energy decreases. Furthermore, the CH and CO stretching modes and their combination bands are effectively excited for the product HCO+ while the bending mode is remarkably excited for the product HOC+.

Commercial Vehicle Intake System Flow Field Mechanism Analysis

The numerical simulation and fluid dynamics simulation of the internal flow field and its influence mechanism of a commercial vehicle intake system were carried out aim at studying the flow field characteristics of the intake system. The internal and surface pressure, velocity, and turbulent kinetic energy distribution of intake systems under the rated operating conditions and three high torque conditions of the engine were analyzed. The simulation results showed that with the increase of the mass flow of the intake air, the pressure distribution on the surface of the intake system increased, and the pressure drop of the inlet and outlet increased rapidly. With the increase of the mass flow, the scale and number of vortexes in the intake system increased sharply. The distribution of turbulent kinetic energy is more related to the velocity field distribution. However the internal turbulent energy distribution of the intake system is concentrated under one condition. As the intake air mass flow rate drops from 1,500 kg/h to 764 kg/h, the pressure drop of the intake system drops from 2,858,566 Pa to 721,411 Pa; the average turbulent energy decreases from 5.41 m2/s2; to 0.896 m2/s2. In this paper, the research on the flow field of the engine intake system aims to provide research directions for the early stage of the structural design of the intake system of large agricultural vehicles.

Parametric study and optimization of the protect system containing a re-entrant hexagon cored sandwich panel under blast impact

In this paper, a protect system consists of a re-entrant hexagon honeycomb cored sandwich panel and a homogenous steel plate was firstly proposed. The parametric study including boundary conditions, geometric and thickness parameters of the protect system was conducted. It was found that, under the presented set-up, the boundary conditions did not affect the energy absorption of the protect system, they only altered the internal energy distribution among the protect system. Finally, a novel multi-scale optimization was conducted to further improve the performance of the protect system. Another conventional multi-objective optimization was also conducted for comparison. The results showed that, by affording less computational effort, the multi-scale optimization improved the ASEA (areal specific energy absorption) by 4.9% and reduced MaxD (maximum displacement) by 1.8%, comparing to the conventional multi-objective optimization.

Investigation of harbor oscillations originated from the vessel-induced bores using methods of autoregressive model and Mahalanobis distance

This paper presents a study for investigating and identifying features of oscillation patterns induced by vessel motions in the context of statistical pattern recognition on the basis of time-domain oscillation series in addition to traditional frequency-domain analysis. Numerical simulations are carried out for a semi-enclosed harbor of variable depth with different vessel motions as external agitation sources and the oscillation responses are measured at multiple locations along the backwall in the longshore direction and along one sidewall in the offshore direction. Vector autoregressive type models are proposed and applied on the recorded oscillation time series. From clustering of the selected vector autoregressive model coefficients fitted to the oscillation responses, both the influences of a changing bathymetry and those of various vessel motions can be recognized, although some of them are insensitive to frequency-domain analysis and cannot be revealed with the amplitude spectra. With Mahalanobis distances calculated from the spatially distributed measurements at observation points within the harbor, an insight into the internal structure and energy distribution of the vessel-induced oscillations can be achieved by extracting the probability density distributions and the occurrence or absence of certain oscillation components or modes can be analyzed with the proposed pattern recognition approach.

Threshold Collision-Induced Dissociation of Hydrated Thorium(IV) Trihydroxide Cation: Experimental and Theoretical Investigation of the Binding Energies for Th(OH)3+(H2O)n Complexes (n = 1-4).

Threshold collision-induced dissociation of Th(OH)3+(H2O)n (n = 1-4) with xenon was performed using a guided ion beam tandem mass spectrometer. The primary dissociation pathway for all complexes is a loss of a single water molecule followed by the sequential loss of additional water molecules at higher collision energies. The data were analyzed using a statistical model after accounting for lifetime effects and reactant internal and kinetic energy distributions to obtain 0 K bond dissociation energies (BDEs). These were also converted using rigid rotor/harmonic oscillator approximations to yield thermodynamic values at room temperature. The 0 K BDEs of H2O ligands to Th(OH)3+ (IV) are experimentally determined for the first time as 106 ± 6, 89 ± 6, 76 ± 4, and 51 ± 4 kJ/mol for the first, second, third, and fourth water ligand added. These values agree reasonably well with values calculated at the B3LYP, B3PW91, and PBE0 levels of theory with aug-cc-pVQZ basis sets, whereas B3LYP-GD3BJ, MP2, and CCSD(T) single point energies with (without) counterpoise corrections systematically overestimate the bond energies by about 15 (20), 19 (25), and (18) kJ/mol, respectively.

Radiative cooling dynamics of anthracene cations stored in DESIREE studied via the time evolution of 2-photon-absorption induced dissociation rate

SynopsisAnthracene cations (C14H10 +) have been stored in the cryogenic (13 K) electrostatic storage ring DESIREE in Stockholm to study their radiative cooling dynamics on a long time scale up to 2 s. By monitoring the laser-induced delayed dissociation curves during the storage, the evolution of the dissociation rate was obtained. Its decrease as a function of time is closely related to the time evolution of the internal energy distribution of the stored anthracene cations and consequently to the energy loss due to radiative cooling, including both Poincaré and infrared fluorescences.

High-order least-square-based finite-difference-finite-volume method for simulation of incompressible thermal flows on arbitrary grids.

In this work, a high-order (HO) least-square-based finite difference-finite volume (LSFD-FV) method together with thermal lattice Boltzmann flux solver (TLBFS) is presented for simulation of two-dimensional (2D) incompressible thermal flows on arbitrary grids. In the present method, a HO polynomial based on Taylor series expansion is applied within each control cell, where the unknown spatial derivatives at each cell center are approximated by least-square-based finite difference (LSFD) scheme. Then the recently developed TLBFS is applied to evaluate the convective and diffusive fluxes simultaneously at the cell interface by local reconstruction of thermal lattice Boltzmann solutions of the density and internal energy distribution functions. The present HO LSFD-FV method is verified and validated by 2D incompressible heat transfer problems. Numerical results indicate that the present method can be effectively and flexibly applied to solve thermal flow problems with curved boundaries on arbitrary grids. Compared with the conventional low-order finite volume method, higher efficiency and lower memory cost make the present HO method more promising for practical thermal flow problems.

Non-self-averaging in the Critical Point of a Random Ising Ferromagnet

In this paper, we review recent results on sample-to-sample fluctuations in a critical Ising model with quenched random ferromagnetic couplings. In particular, in terms of the renormalized replica Ginzburg–Landau Hamiltonian in dimensions D < 4 an explicit expression for the probability distribution function (PDF) of the critical free energy fluctuations is derived. Next, using known fixed-point values for the renormalized coupling parameters the universal curve for such PDF in the dimension D = 3 is obtained. For the specific case of the two-dimensional Ising model, using replica calculations in the renormalization group framework, we derive explicit expressions for the PDF of the critical internal energy and for the specific heat fluctuations. It is shown that the disorder distribution of internal energy is Gaussian, and its typical sample-to-sample fluctuations as well as its average value scale with the system size L like ~ Llnln(L). In contrast, the specific heat is shown to be self-averaging with a distribution function that tends to a δ-peak in the thermodynamic limit L → ∞.

Internal Energy Deposition in Infrared Matrix-Assisted Laser Desorption Electrospray Ionization With and Without the Use of Ice as a Matrix.

The internal energy deposited into analytes during the ionization process largely influences the extent of fragmentation, thus the appearance of the resulting mass spectrum. The internal energy distributions of a series of para-substituted benzyl pyridinium cations in liquid and solid-state generated by infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) were measured using the survival yield method, of which results were subsequently compared with conventional electrospray ionization (ESI). The comparable mean internal energy values (e.g., 1.8-1.9eV at a collision energy of 15eV) and peak widths obtained with IR-MALDESI and ESI support that IR-MALDESI are essentially a soft ionization technique where analytes do not gain considerable internal energy during the laser-induced desorption process and/or lose energy during uptake into charged electrospray droplets. An unusual fragment ion, protonated pyridine, was only found for solid IR-MALDESI at relatively high collision energies, which is presumably resulted from direct ionization of the pre-charged analytes in form of salts. Analysis of tissue with an ice layer consistently yielded ion populations with higher internal energy than its counterpart without an ice layer, likely due to a substantially enhanced number of IR absorbers with ice. Further measurements with holo-myoglobin show that IR-MALDESI-MS retains the noncovalently bound heme-protein complexes under both native-like and denaturing conditions, while complete loss of the heme group occurred in denaturing ESI-MS, showing that the softness of IR-MALDESI is equivalent or superior to ESI for biomolecules.

Ultraviolet photodissociation dynamics of DNCO + hν → D + NCO: Two competitive pathways

Photodissociation dynamics of DNCO + hν → D + NCO at photolysis wavelengths between 200 and 235 nm have been studied using the D-atom Rydberg tagging time-of-flight technique. Product translational energy distributions and angular distributions have been determined. Nearly statistical distribution of the product translational energy with nearly isotropic angular distribution was observed at 210–235 nm, which may come from the predissociation pathway of internal conversion from S1 to S0 state followed by decomposition on S0 surface. At shorter photolysis wavelengths, in addition to the statistical distribution, another feature with anisotropic angular distribution appears at high translational energy region, which can be attributed to direct dissociation on S1 surface. Compared with HNCO, the direct dissociation pathway for DNCO photodissociation opens at higher excitation energy. According to our assignment of the NCO internal energy distribution, dominantly bending and a little stretching excited NCO was produced via both dissociation pathways.

Распределение внутренней энергии в окрестности вершины трещины нормального отрыва

Распределение внутренней энергии в окрестности вершины трещины нормального отрыва

Direct molecular simulation of internal energy relaxation and dissociation in oxygen

A variant of the direct simulation Monte Carlo (DSMC) method, referred to as direct molecular simulation (DMS), is used to study oxygen dissociation from first principles. The sole model input to the DMS calculations consists of 12 potential energy surfaces that govern O2 + O2 and O + O2 collisions, including all spin-spatial degenerate configurations, in the ground electronic state. DMS calculations are representative of the gas evolution behind a strong shock wave, where molecular oxygen excites rotationally and vibrationally before ultimately dissociating and reaching a quasi-steady-state (QSS). Vibrational relaxation time constants are presented for both O2 + O2 and O + O2 collisions and are found to agree closely with experimental data. Compared to O2 + O2 collisions, vibrational relaxation due to O + O2 collisions is found to be ten times faster and to have a weak dependence on temperature. Dissociation rate constants in the QSS dissociation phase are presented for both O2 + O2 and O + O2 collisions and agree (within experimental uncertainty) with rates inferred from shock-tube experiments. Both experiments and simulations indicate that the QSS dissociation rate coefficients for O + O2 interactions are about two times greater than the ones for O2 + O2. DMS calculations predict this to be a result of nonequilibrium (non-Boltzmann) internal energy distributions. Specifically, the increased dissociation rate is caused by faster vibrational relaxation, due to O + O2 collisions, which alters the vibrational energy distribution function in the QSS by populating higher energy states that readily dissociate. Although existing experimental data appear to support this prediction, experiments with lower uncertainty are needed for quantitative validation. The DMS data presented for rovibrational relaxation and dissociation in oxygen could be used to formulate models for DSMC and computational fluid dynamics methods.