Reaction Rate Theory Research Articles

Calculation of excess Gibbs energy of activation for viscous flow in (ionic liquid + co-solvent)

Recently, a comment was published (J. Chem. Thermodyn. 106 (2017), pp. 216–217) regarding the calculation of the (molar) excess Gibbs energy of activation for viscous flow (ΔGmE∗) in binary mixtures of (ionic liquids+solvent). In that comment, it was suggested that the functional form we reported was in error. Here, we show that direct substitution of Eyring’s Theory of Absolute Reaction Rates into the excess Gibbs energy expression that the functional form presented in our original work indeed holds true.

Mobility of nanofiber, nanorod, and straight-chain nanoparticles in gases

ABSTRACTWith the fast development of nanotechnology, accurate measurement and classification of nanoparticles are in great need. Nanoparticles frequently appear in non-spherical forms such as long aspect ratio nanofibers, nanotubes, and irregular nano-agglomerates. While the well-developed classical studies were mainly in continuum regime with spherical particles, dynamics of the non-spherical nanoparticles is not fully understood. In this study, orientation-averaged mobility of nanofiber and nanorod (with no preferred alignment) is examined by the methods of Brownian diffusion theory, a combination of collision limited reaction rate theory and the bipolar diffusion charging analysis. Comparisons to empirical predictions from the experimental measurements are also made. The study leads to the discovery of a surface-dominated mobility for high aspect ratio nanoparticles with characteristic Knudsen number greater than 5. In view of the extreme relative length scales between particle size and the gas mean fr...

Tuning the glass transition of asphalt binder based on viscosity criteria under zero shear rates

With the theory of absolute reaction rate or transition-state approach together with the boundary perturbation method we calculate the possible temperature-dependent viscosity of bitumen or asphalt binder via tuning of activation volume as well as activation energy for the first time under zero shear rates. Before we present our novel approach and numerical results we firstly verify our calculations with both ambient temperature and high temperature viscosity measurements for bitumen conducted previously. Our tuning activation volume of bitumen will be useful to the current needs of intelligent compaction and application of nanotechnology to easily handling or processing asphalt binder.

RNA synthesis is associated with multiple TBP-chromatin binding events

Competition ChIP is an experimental method that allows transcription factor (TF) chromatin turnover dynamics to be measured across a genome. We develop and apply a physical model of TF-chromatin competitive binding using chemical reaction rate theory and are able to derive the physical half-life or residence time for TATA-binding protein (TBP) across the yeast genome from competition ChIP data. Using our physical modeling approach where we explicitly include the induction profile of the competitor in the model, we are able to estimate yeast TBP-chromatin residence times as short as 1.3 minutes, demonstrating that competition ChIP is a relatively high temporal-resolution approach. Strikingly, we find a median value of ~5 TBP-chromatin binding events associated with the synthesis of one RNA molecule across Pol II genes, suggesting multiple rounds of pre-initiation complex assembly and disassembly before productive elongation of Pol II is achieved at most genes in the yeast genome.

A Unified Constitutive Model for Creep and Cyclic Viscoplasticity Behavior Simulation of Steels Based on the Absolute Reaction Rate Theory

In this work, the viscoplasticity and creep behavior for modified 9Cr-1Mo and 316 stainless steels were investigated. Based on the absolute reaction rate theory, a unified constitutive model incorporating internal state variables was proposed to characterize the evolution of the back stress. Also, the model was implemented by the ABAQUS system with the semi-implicit stress integration. Compared to the experimental data, the results demonstrated that the proposed approach could effectively simulate the cyclic softening and hardening behavior for such structural steels.

Micromechanism of Thermally Induced Breaking of One-Dimensional Nanocrystals

Thermo-fluctuation model of failure of one-dimensional nanocrystals is offered for wide range of change in temperature, time and applied loading. Unlike the classic models, which are based on the theory of reaction rates, in present model the failure initiation is related to the instability of atomic interaction. It enables to account for the effect of both temperature and applied loading on the lifetime of crystal within a framework of the unified approach. The model proposed was employed to predict the temperature dependence of both strength and lifetime of carbyne nanoconductor (CNC). Obtained temperature dependences agree well with the MD-simulation findings. Within the framework of the above model, CNC lifetime was estimated. It is exhibited that for temperatures not higher than 600K, CNC have a long-lasting lifetime, so, they can be used in nanodevices.

Modeling phase decomposition and patterning in binary alloy systems subjected to neutron irradiation

ABSTRACTWe study processes of phase decomposition and patterning in a model of a binary alloy system subjected to sustained irradiation. We exploit the reaction rate theory and generalize the Darken approach of vacancy diffusion to describe generation, recombination, annihilation and spatial interaction of point defects. It is shown that an increase in the defect production rate phase, decomposition processes are replaced by disordering and patterning with vacancy clusters' formation. At elevated damage rates, both phase separation and patterning are accompanied by pattern selection processes. In the framework of numerical simulations, dynamics of phase decomposition and vacancy clusters formation is studied in detail. A change in the morphology of vacancy clusters during irradiation and their statistical properties are discussed.

Possible anomalous transitional transport of electronic fluids in hydrogen sulphide under high pressures

With the verified quantum chemistry theory of absolute reaction rate or transition state approach, we illustrate the possible enhancing superconducting transition temperature of hydrogen sulphide under high pressures via tuning of activation volume together with activation energy for the first time under zero shear rates. Before we present our novel approach and numerical results we firstly verify our preliminary results with previous Drozdov et al.’s [Nature2015, 525, 73] measurements. After some necessary verifications, we illustrate our novel numerical results via the enhancing of the onset or superconducting transition temperature for electronic liquids in hydrogen sulphide within the same lower pressure regime (compared to previous Drozdov et al.’s experimental data) by decreasing of activation volume: ∼ 10−25m3 decrement under zero shear rates. The latter might also be linked to the glass transition state for electronic fluids in hydrogen sulphide under high pressures once the shear viscosity is calculated.

Analyses of Transient and Tertiary Small Punch Creep Deformation of 316LN Stainless Steel

Creep deformation behavior of 316LN stainless steel (SS) under small punch creep (SPC) and uniaxial creep test has been assessed and compared at 923 K (650 °C). The transient and tertiary creep deformation behaviors have been analyzed according to the equation proposed for SPC deflection, \( \delta = \delta_{0} + \delta_{\text{T}} \cdot (1 - {\text{e}}^{ - \kappa \cdot t} ) + \dot{\delta }_{\text{s}} t + \delta_{3} {\text{e}}^{{\left[ {\varphi \left( {t - t_{\text{r}} } \right)} \right]}} \) on the basis of Dobes and Cadek equation for uniaxial creep strain. Trends in the variations of (i) rate of exhaustion of transient creep (κ) with steady-state deflection rate (\( \dot{\delta }_{\text{s}} \)) (ii) ‘κ’ with time to attain steady-state deflection rate, and (iii) initial creep deflection rate with steady-state deflection rate implied that transient SPC deformation obeyed first-order reaction rate theory. The rate of exhaustion of transient creep (r′) values that were determined from uniaxial creep tests were correlated with those obtained from SPC tests. Master curves representing transient creep deformation in both SPC and uniaxial creep tests have been derived and their near coincidence brings unique equivalence between both the test techniques. The relationships between (i) rate of acceleration of tertiary creep (φ) and steady-state deflection rate, (ii) ‘φ’ and time spent in tertiary stage, and (iii) final creep deflection rate and steady-state deflection rate revealed that first-order reaction rate theory governed SPC deformation throughout the tertiary region also. Interrelationship between the transient, secondary, and tertiary creep parameters indicated that the same mechanism prevailed throughout the SPC deformation.

Kinetic modeling of the thermal destruction of mustard gas

The destruction of stockpiles or unexploded ammunitions of bis(2-chloroethyl) sulfide, also called mustard gas or yperite, by thermal treatments requires the development of highly safe processes. The high-level of toxicity of this compound induces a high level of complexity for any experiments. Consequently, there is a considerable lack of knowledge on the behavior of this chemical under high-temperature conditions (with or without oxygen). In this work a detailed chemical kinetic model for the combustion and pyrolysis of mustard gas is proposed for the first time. A large number of thermo-kinetic parameters were calculated using quantum chemistry and reaction rate theory. The model was validated against experimental pyrolysis data of the literature. It was shown that the degradation of mustard gas is ruled by a chain reaction mechanism where the chlorine atom is the principal chain carrier. HS radical, formed in the primary mechanism by an original pathway found using quantum calculations, was also proved to be an important chain carrier. Comparison with the kinetics of the usual simulant of mustard gas, diethyl sulfide, showed that the lack of chlorine atom in the former chemical leads to an inappropriate simulation of the mustard gas behavior. Combustion and pyrolysis simulations were also compared and surprisingly demonstrated that chlorine atoms remain the main chain carrier in combustion.

On Products and Ratios of Three or More Generalized Gamma Variables

This paper deals with the distributions of products and ratios involving three real scalar generalized gamma random variables. Product and certain types of ratios are defined and their distributional properties are examined. It is shown that some forms provide extensions of reaction-rate probability integrals in nuclear reaction-rate theory, Kratzel integral and Kratzel transforms, Bayesian procedures, statistical densities of products and ratios.

Thermal Decomposition of 3-Bromopropene. A Theoretical Kinetic Investigation.

A detailed kinetic study of the gas-phase thermal decomposition of 3-bromopropene over wide temperature and pressure ranges was performed. Quantum chemical calculations employing the density functional theory methods B3LYP, BMK, and M06-2X and the CBS-QB3 and G4 ab initio composite models provide the relevant part of the potential energy surfaces and the molecular properties of the species involved in the CH2═CH-CH2Br → CH2═C═CH2 + HBr (1) and CH2═CH-CH2Br → CH2═CH-CH2 + Br (2) reaction channels. Transition-state theory and unimolecular reaction rate theory calculations show that the simple bond fission reaction ( 2 ) is the predominant decomposition channel and that all reported experimental studies are very close to the high-pressure limit of this process. Over the 500-1400 K range a rate constant for the primary dissociation of k2,∞ = 4.8 × 10(14) exp(-55.0 kcal mol(-1)/RT) s(-1) is predicted at the G4 level. The calculated k1,∞ values lie between 50 to 260 times smaller. A value of 10.6 ± 1.5 kcal mol(-1) for the standard enthalpy of formation of 3-bromopropene at 298 K was estimated from G4 thermochemical calculations.

Room-temperature superconducting in sulfur hydrides

With the theory of absolute reaction rate we demonstrate the possible superconducting transition in sulfur hydrides within the room-temperature regime via tuning of activation volume as well as activation energy for the first time under zero shear rates. Before we present our novel approach and numerical results we firstly verify our calculations with previous measurements [Drozdov et al. Nature 525 (2015) 73]. After successful verifications, we illustrate our novel numerical results via the enhancing transition temperature for electronic liquids in sulfur hydrides to within the room-temperature regime (after decreasing of activation volume: ∼10−27m3 decrement or increasing of activation energy under zero shear rates compared to previous Drozdov et al.'s experimental data).

Thermal effects on van der Waals adhesive forces

We present an experimental and theoretical study on how thermal energy alters van der Waals adhesion forces in nanoscale contacts stretched by mechanical probes. The force follows a distribution whose density function is an asymmetric bell-shaped curve presenting a temperature-dependent negative skewness. With increasing temperature the asymmetry increases whereas the most probable force value decreases. Using a 2--8 Lennard-Jones interaction potential within the reaction rate theory, we offer a theoretical framework permitting an evaluation of the microscopic parameters governing adhesion in a van der Waals nanocontact subjected to mechanical fluctuations.

Effective dynamics along given reaction coordinates, and reaction rate theory.

In molecular dynamics and related fields one considers dynamical descriptions of complex systems in full (atomic) detail. In order to reduce the overwhelming complexity of realistic systems (high dimension, large timescale spread, limited computational resources) the projection of the full dynamics onto some reaction coordinates is examined in order to extract statistical information like free energies or reaction rates. In this context, the effective dynamics that is induced by the full dynamics on the reaction coordinate space has attracted considerable attention in the literature. In this article, we contribute to this discussion: we first show that if we start with an ergodic diffusion process whose invariant measure is unique then these properties are inherited by the effective dynamics. Then, we give equations for the effective dynamics, discuss whether the dominant timescales and reaction rates inferred from the effective dynamics are accurate approximations of such quantities for the full dynamics, and compare our findings to results from approaches like Mori-Zwanzig, averaging, or homogenization. Finally, by discussing the algorithmic realization of the effective dynamics, we demonstrate that recent algorithmic techniques like the "equation-free" approach and the "heterogeneous multiscale method" can be seen as special cases of our approach.

Reaction rate theory: summarising remarks.

This paper summarizes the contributions to the Faraday Discussion on reaction rate theory. The topics range from contemporary usage of transition state theory, including rare event sampling, to instantons and non-adiabatic dynamics.

Rate Coefficient for the (4)Heμ + CH4 Reaction at 500 K: Comparison between Theory and Experiment.

The rate constant for the H atom abstraction reaction from methane by the muonic helium atom, Heμ + CH4 → HeμH + CH3, is reported at 500 K and compared with theory, providing an important test of both the potential energy surface (PES) and reaction rate theory for the prototypical polyatomic CH5 reaction system. The theory used to characterize this reaction includes both variational transition-state (CVT/μOMT) theory (VTST) and ring polymer molecular dynamics (RPMD) calculations on a recently developed PES, which are compared as well with earlier calculations on different PESs for the H, D, and Mu + CH4 reactions, the latter, in particular, providing for a variation in atomic mass by a factor of 36. Though rigorous quantum calculations have been carried out for the H + CH4 reaction, these have not yet been extended to the isotopologues of this reaction (in contrast to H3), so it is important to provide tests of less rigorous theories in comparison with kinetic isotope effects measured by experiment. In this regard, the agreement between the VTST and RPMD calculations and experiment for the rate constant of the Heμ + CH4 reaction at 500 K is excellent, within 10% in both cases, which overlaps with experimental error.

Physicochemical analysis of slip flow phenomena in liquids under nanoscale confinement

Eyring theory employs the statistical mechanical theory of absolute reaction rates to analyse the transport mechanisms in fluids. A physicochemical methodology combining molecular dynamics (MD) and Eyring theory of reaction rates is proposed for investigating the liquid slip on a solid wall in the nanoscale domain. The method involves the determination of activation energy required for the flow process directly from the MD trajectory information and then calculate the important transport properties of the confined fluid from the activation energy. In order to demonstrate the universal applicability of the proposed methodology in nanofluidics, the slip flow behavior of argon, water and ionic liquid confined in various nanostructures has been investigated. The slip length is found to be size dependent in all the cases. The novelty of this method is that the variations in slip length are explained on the basis of molecular interactions and the subsequent changes in the activation energy.

Application of the Eyring Equation in the Evaluation of Semi-Solid Forming-Induced Si Particle Refinement in the Hypereutectic Al-Si Alloys

On the basis of Eyring’s theory of absolute reaction rate, an approach to modeling Si particle refinement acceleration in the semi-solid forming of a hypereutectic Al-Si alloy has been developed. The acceleration variable data used in the present analysis were obtained from a semi-solid compression test using Al-25 mass pct Si alloy cylindrical specimens with a diameter of 15 mm and a height of 15 mm; the test conditions comprised a combination of compression displacements ∆h = 5, 10, and 12 mm; compression rates v = 5, 25, and 125 mm/min; and test temperatures T = 853 K and 863 K (580 °C and 590 °C). The coarse primary Si particle refinement depends on a complex interaction among variables, such as compression displacement, compression rate, and test temperature. The performance of Si particle refinement degraded under higher temperature, slower strain rates, and slower shear rates. The results of the Si particle size are suitably summarized by the Eyring equation as a function of the temperature and the shear rate. The baseline Si particle size and the baseline temperature of Si particle refinement, i.e., the reference temperature, were GN = 0.27 mm and TN = 866.4 K (593.4 °C), respectively. The calculated results using this equation correlated well with the observed results. An acceleration factor of Si particle refinement was successfully derived on the basis of this equation and indicated that operating at a higher shear rate and a temperature just above the melting point of eutectic Al-Si alloy are the optimum conditions for refining Si particles.

Theoretical Kinetics Study of the Reactions Forming the ClCO Radical Cycle in the Middle Atmosphere of Venus

Abstract A quantum-chemistry and kinetics study of key chemical reactions involved in the ClCO radical cycle of the Venus atmosphere: Cl + CO + M → ClCO + M (1); ClCO + O2 + M → ClC(O)OO + M (2) and ClC(O)OO + Cl → CO2 + ClO + Cl (3) (M = CO2), has been performed at 150–300 K. Unimolecular reaction rate theories on potential energy features derived at the G4//B3LYP/6-311+G(3df) ab initio composite level were employed. Limiting low pressure rate coefficients calculated for Reaction (1) are in good agreement with recommended experimental values. The present results validate rate coefficient values measured for Reaction (2) over relevant strato-mesosphere Venusian conditions. Rate coefficients calculated by the SACM/CT for Reaction (3) are given by k 3 = 2.5 × 10−11 (T/300)0.5 cm3 molecule –1 s –1. In the absence of experimental data, these values provide the first reliable prediction for k 3.