Application Of Transition State Theory Research Articles

Solute–solvent and solvent–solvent interactions of menthol in isopropyl alcohol and its binary mixtures with methyl salicylate by volumetric, viscometric, interferometric and refractive index techniques

The apparent molar volume ( V ∅ ), viscosity B-coefficient, isoentropic compressibility ( ϕ K ) of menthol have been determined in binary solution of isopropyl alcohol and methyl salicylate (at 303.15, 313.15 and 323.15 K) from density ( ρ), viscosity ( η) and sound speed respectively. The apparent molar volumes have been extrapolated to zero concentration to obtain the limiting values at infinite dilution using Masson equation. The infinite dilution partial molar expansibilities have also been calculated from the temperature dependence of the limiting apparent molar volumes. Viscosity B-coefficients has been calculated using Jones–Dole equation. The structure-making or breaking capacity of the solute under investigation has been discussed in terms of sign of ( δ 2 V Ø o / δ T 2 ) P . The activation parameters of viscous flow were determined and discussed by application of transition state theory.

Lifetimes of compounds made of noble-gas atoms with water

The kinetic stability of the HXeOH and HXeOXeH molecules, chemically bound compounds made of Xe atoms and water, is studied by multi-reference ab initio methods. The decomposition paths, the transition states and the rates of dissociation as a function of temperature, are calculated. HXeOH and HXeOXeH are found to be protected by an energy barriers of 0.59 and 0.4 eV, respectively. Applying transition state theory, HXeOH and HXeOXeH have intrinsic half-lives of 1 h at 170 and 120 K, respectively. Implications of the results for the kinetic stability of these species are discussed.

Studies on Molecular Interactions of Some Thiocyanate Salts in Coaqueous Solutions of 1,3-Dioxolane + Water by Volumetric, Viscometric, and Speed of Sound Measurements

The densities and viscosities of some thiocyanate compounds, viz., ammonium thiocyanate, sodium thiocyanate, and potassium thiocyanate, in 10 %, 20 %, and 30 % by mass of 1,3-dioxolane + water mixtures have been determined at T = (298.15, 308.15, and 318.15) K and p = 0.1 MPa. The speeds of sound of the thiocyanate compounds in 10 %, 20 %, and 30 % by mass of 1,3-dioxolane + water mixtures have also been determined at 298.15 K. Apparent molar volumes (Vϕ), viscosity B-coefficients, and adiabatic compressibility (β) of these electrolytes were obtained from their densities, viscosities, and speed of sound data. The limiting apparent molar volumes (Vϕo) and experimental slopes (Sv*) derived from the Masson equation and the obtained parameters have been interpreted in terms of ion−solvent and ion−ion interactions, respectively. The viscosity data were evaluated by using the Jones−Dole equation. The structure making/breaking capacities of the electrolytes have been inferred from the sign of (δ2ϕVo/δT2)p and dB/dT. The activation parameters of viscous flow for the ternary solutions studied were also calculated and explained by the application of transition state theory.

Partial Molar Volumes and Viscosity B-Coefficients of Nicotinamide in Aqueous Resorcinol Solutions at T = (298.15, 308.15, and 318.15) K

Partial molar volumes \({( {\phi _{\rm v}^{\rm o}} )}\) and viscosity B-coefficients for nicotinamide in (0.00, 0.05, 0.10, 0.15, and 0.20) mol·dm−3 aqueous resorcinol solutions have been determined from solution density and viscosity measurements at (298.15, 308.15, and 318.15) K as a function of the concentration of nicotinamide (NA). Here the relation \({\phi _{v}^{\rm o} =a_0 +a_{1} T+a_{2} T^{2}}\), has been used to describe the temperature dependence of the partial molar volume \({\phi _v^{\rm o} }\). These results and the results obtained in pure water were used to calculate the standard volumes of transfer \({\Delta \phi _{v}^{\rm o} }\) and viscosity B-coefficients of transfer of nicotinamide from water to aqueous resorcinol solutions to study various interactions in the ternary solutions. The partial molar volume \({( {\phi _{v}^{\rm o}})}\) and experimental slopes obtained from the Masson equation have been interpreted in terms of solute–solvent and solute–solute interactions, respectively. The viscosity data have been analyzed using the Jones–Dole equation, and the derived parameters B and A have also been interpreted in terms of solute–solvent and solute–solute interactions, respectively, in the ternary solutions.The structure making or breaking ability of nicotinamide has been discussed in terms of the sign of \({( {\delta ^{2}\phi _v^o /\delta T^{2}})_P}\). The activation parameters of viscous flow for the ternary solutions studied were also calculated and explained by the application of transition state theory.

Ion-solvent and ion-ion interactions of phosphomolybdic acid in aqueous solution of catechol at 298.15, 308.15, and 318.15 K

Apparent molar volume (VO) and viscosity B-coefficients were measured for phosphomolybdicacid in aqueous solution of catechol from solution density (ρ) and viscosity (η) at 298.15, 308.15, and 318.15 K at various solute concentrations. The experimental density data were evaluated by Masson equation and the derived data were interpreted in terms of ion-solvent and ion-ion interactions. The viscosity data have been analyzed using Jones-Dole equation and the derived parameters, B and A, have been interpreted in terms of ion-solvent and ion-ion interactions respectively. The structure-making or breaking capacity of the solute under investigation has been discussed in terms of sign of (δ2VOo/δT2)P. The activation parameters of viscous flow were determined and discussed by application of transition state theory.

Apparent molar volume, viscosity, and adiabatic compressibility of some mineral sulfates in aqueous binary mixtures of formamide at 298.15, 308.15, and 318.15 K

The densities and viscosities of several sulfates, viz., ammonium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, zinc sulfate and cadmium sulfate in aqueous binary mixtures of formamide (FA) have been determined at 298.15, 308.15, and 318.15 K and at atmospheric pressure. The ultrasonic speeds of the electrolytic solutions have also been measured at 298.15 K. Apparent molar volumes (ϕ V ), viscosity B-coefficients and adiabatic compressibilities (K S) of these electrolytic solutions were calculated from the experimental densitiy, viscosity and acoustic data. The density and viscosity data were evaluated by using Masson’s and Jones-Dole equation respectively; the derived parameters have been analyzed in terms of ion-ion and ion-solvent interactions. The structure making/breaking capacities of the electrolytes have been inferred from the sign of (∂2ϕ 0 /∂T 2) P . The results showed that all the electrolytes act as structure-makers in these media. Also the compressibility data indicated electrostriction of the solvent molecules around the cations. The activation parameters of viscous flow were also determined and discussed by the application of transition state theory.

The simultaneous reduction of nitric oxide and soot in emissions from diesel engines

Recent studies demonstrate that the decomposition of nitric oxide on a soot molecule forms surface nitrogen and oxygen. The surface nitrogen can be recombined to gaseous N 2 while the surface oxygen desorbs from the soot molecule as CO. This non-catalytic conversion of gaseous NO into N 2 is investigated using density functional theory, transition state theory and a kinetic Monte-Carlo (kMC) simulation. The results are validated against experiments. A mechanism for the conversion of NO to N 2 on a soot surface is explored. The geometries of the intermediate stable species as well as the transition states were optimized to identify the different reaction steps. The forward and backward reaction rate of each intermediate reaction is calculated applying transition state theory. A kMC simulation using the current rates and intermediate species demonstrates feasible mechanisms for the conversion of NO to N 2 on a soot surface. It is also suggested that a portion of NO is trapped on the soot surface and this increases during the reaction and blocks the active carbon sites inhibiting further reactions. By combining different theoretical techniques in a multi-scale model, we are able to describe the conversion of soot in the presence of NO accurately.

Volumetric and Viscometric Studies of Some Metal Acetates in Aqueous Solutions at T = (288.15 to 318.15) K

Precise density and viscosity measurements on aqueous solutions of lithium acetate, sodium acetate, potassium acetate, magnesium acetate, and calcium acetate have been carried out in the temperature range of T = (288.15 to 318.15) K using a vibrating-tube digital densimeter and Micro-Ubbelohde type capillary viscometer, respectively. The data have been used to obtain partial molar volumes at infinite dilution, V2o, and viscosity B-coefficients for these salts. The effect of temperature on these thermodynamic properties has been studied by determining the partial molar expansibilities (∂V2o/∂T)P and (∂2V2o/∂T2)P and (∂B/∂T) coefficients. The activation free energies, Δμ20,⧺, for the viscous flow of solutions have also been obtained by application of transition state theory to the viscosity B-coefficient data. The results have been rationalized in terms of various interactions taking place in these solutions.

Ion–solvent and ion–ion interactions of sodium molybdate and sodium tungstate in mixtures of ethane-1,2-diol and water at 298.15, 308.15 and 318.15 K

Apparent molar volume ( V Ø) and viscosity B-coefficients were estimated for sodium molybdate and sodium tungstate in aqueous binary mixture of ethane-1,2-diol from measured solution density ( ρ) and viscosity ( η) at 298.15, 308.15 and 318.15 K at various electrolyte concentrations. The experimental density data were evaluated by Masson equation and the derived data were interpreted in terms of ion–solvent and ion–ion interactions. The viscosity data has been analyzed using Jones–Dole equation and the derived parameters, B and A, have also been interpreted in terms of ion–solvent and ion–ion interactions respectively. The structure-making or breaking capacity of the electrolyte under investigation has been discussed in terms of sign of ( δ 2V Ø 0 / δT 2) P . The activation parameters of viscous flow were also determined and were discussed by the application of transition state theory.

Apparent molar volumes and viscosity B-coefficients of nicotinamide in aqueous tetrabutylammonium bromide solutions at T = (298.15, 308.15, and 318.15) K

Apparent molar volumes ϕ V and viscosity B-coefficients for nicotinamide in (0.00, 0.05, 0.10, and 0.15) mol · dm −3 aqueous tetrabutylammonium bromide (TBAB) solutions have been determined from solution density and viscosity measurements at temperatures over the range (298.15 to 318.15) K as function of concentration of nicotinamide (NA). In the investigated temperature range, the relation: ϕ V ∘ = a 0 + a 1 T + a 2 T 2 , have been used to describe the temperature dependence of the standard partial molar volumes ϕ V ∘ . These results have, in conjunction with the results obtained in pure water, been used to deduce the standard volumes of transfer Δ ϕ V ∘ and viscosity B-coefficients of transfer for nicotinamide from water to aqueous TBAB solutions for rationalizing various interactions in the ternary solutions. The structure making or breaking ability of nicotinamide has been discussed in terms of the sign of ( δ 2 ϕ V ∘ / δ T 2 ) P . An increase in the transfer volume of nicotinamide with increasing TBAB concentration has been explained by Friedman–Krishnan co-sphere model. The activation parameters of viscous flow for the ternary solutions investigated were also determined and discussed by the application of transition state theory.

Methods for calculating the desorption rate of an isolated molecule from a surface: Water on MgO(0 0 1)

We present two types of Molecular Dynamics (MD) simulation for calculating the desorption rate of molecules from a surface. In the first, the molecules move freely between two surfaces, and the desorption rate is obtained either by counting the number of desorption events in a given time, or by looking at the average density of the molecules as a function of distance from the surface and then applying transition state theory (TST). In the second, the potential of mean force (PMF) for a molecule is determined as a function of distance from the surface and the desorption rate is obtained by means of TST. The methods are applied to water on the MgO(0 0 1) surface at low coverage. Classical potentials are used so that long simulations can be performed, to minimise statistical errors. The two sets of MD simulations agree well at high temperatures. The PMF method reproduces the 0 K adsorption energy of the molecule to within 5 meV, and finds that the well depth of the PMF is not linear with temperature. This implies the prefactor frequency f in the Polanyi–Wigner equation is a function of temperature, increasing at lower temperatures due to the reduction of the available configuration space associated with an adsorbed molecule compared with a free molecule.

Effects of organic matter on phosphorus release kinetics in different trophic lake sediments and application of transition state theory

Sediments have a significant influence on the overlying water, and phosphorus (P) release from sediments is an important source for the lake eutrophication, particularly in shallow ones. In this study, effects of organic matter on P release from sediments in different trophic lakes from the middle and lower reaches of Yangtze River, China, were investigated, and the release kinetics of different P fractions at different temperature were studied. The results show that the release kinetics of soluble reactive phosphorus (SRP), dissolved organic phosphorus (DOP) and dissolved total phosphorus (DTP) were similar for the studied sediments, the release rate increased rapidly in the initial hours, and it increased gradually after 10 h. The release kinetics of SRP, DOP and DTP followed the Power Function model. SRP was the major fraction among the released DTP, while DOP was an important fraction in the heavily polluted sediments. Organic matter restricted the SRP and DTP release while it promoted the DOP release. Both DOP and SRP release processes were endothermic. The thermodynamic properties in the P release kinetics were calculated and discussed.

Crystal dissolution kinetics and Gibbs free energy

The dependence of dissolution rates on the difference of Gibbs free energy is of critical importance for our understanding of crystal dissolution, reactive flow models and their applications to a variety of environmentally related problems. Here, we review experimental data generated with mineral powders and single crystals to develop a better understanding of apparent inconsistencies between otherwise internally consistent data sets. Additional information from direct surface observations and measurements with vertical scanning interferometry (VSI) and atomic force microscopy (AFM) of albite dissolution at 25, 150 and 185 °C may shed new light on this old but unsolved question. Our discussion is based on the importance of etch pit development, its Δ G dependence, and the pits’ role as a source for steps and step movement in the dissolution process. Results indicate that reaction history may be of critical importance in determining the overall reaction mechanism and its rate. Different rates are observed for systems having otherwise identical Δ G r acquired from increasing versus decreasing disequilibrium positions. In this context, we finally discuss the validity of the common application of transition state theory (TST) to elementary and overall reactions governing the dissolution process. In this discussion of crystal dissolution, we contrast TST applications with a stochastic, many-body treatment that has led to the development of a stepwave model. This discussion also focuses on the controversy caused by the rivalry between surface adsorption models and a probabilistic model that seeks to incorporate the full three-dimensional crystal structure.

Application of transition state theory to the study of materials containing acryloxy and acrylate units

We study the diffusion behavior of a probe, in monomers containing acryloxy and acrylate units that are commonly used in restorative dentistry. We apply a version of transition state theory with satisfactory results. Results show that transition state theory describes part of the underlying physics successfully thus reinforcing its applicability as a complement and extension to molecular dynamics simulations.

Locating stationary points of sorbate-zeolite potential energy surfaces using interval analysis

The diffusion of a sorbate molecule in a zeolite can be studied using transition-state theory. In this application, and other applications of transition-state theory, finding all local minima and saddle points of the potential energy surface is a critical computational step. A new strategy is described here for locating stationary points on a potential energy surface. The methodology is based on interval analysis, and provides a mathematical and computational guarantee that all stationary points will be found. The technique is demonstrated using potential energy surfaces arising in the use of transition-state theory to study the diffusion of three sorbates, xenon, methylene, and sulfur hexafluoride, at infinite dilution in silicalite.

Molecular-dynamics analysis of the diffusion of molecular hydrogen in all-silica sodalite.

In order to investigate the technical feasibility of crystalline porous silicates as hydrogen storage materials, the self-diffusion of molecular hydrogen in all-silica sodalite is modeled using large-scale classical molecular-dynamics simulations employing full lattice flexibility. In the temperature range of 700-1200 K, the diffusion coefficient is found to range from 1.610(-10) to 1.810(-9) m(2)/s. The energy barrier for hydrogen diffusion is determined from the simulations allowing the application of transition state theory, which, together with the finding that the pre-exponential factor in the Arrhenius-type equation for the hopping rate is temperature-independent, enables extrapolation of our results to lower temperatures. Estimates based on mass penetration theory calculations indicate a promising hydrogen uptake rate at 573 K.

04/00937 Reaction mechanism of mercury and gases during coal combustion: Liu, J. et al. Gongcheng Rewuli Xuebao, 2003, 24, (1), 161–164. (In Chinese)

Predicting emissions of mercury and the speciation of mercury in combustion emissions cannot be done without a fundamental understanding of the chemical reaction mechanism of mercury in flue gas. The microcosmic mechanism of reaction between mercury and gases was studied by ab initio calculations of quantum chemistry. The geometry optimizations of reactant, transition state, intermediate and product were made at MP2/SDD level. The reaction potential barriers and enthalpy were calculated. The rate constant was derived by application of transition state theory and compared with the data of reference. The results show that quantum chemistry is an effective method to study the reaction mechanism of trace elements and gas during coal combustion.

Volumetric and viscometric properties of urea and D-glucose in aqueous glycine at 308 K

Density, viscosity and refractive index data for urea and D-glucose in (0.01, 0.02 and 0.03 M) glycine + water mixed solvent as a function of urea/glucose concentration are presented at 308 K. The density data have been used to obtain limiting apparent molar volume (Φ 0 v ) and the slope (S* v ) using Masson's equation. The viscosity data are analysed by means of Jones-Dole equation. The activation parameters of viscous flow, namely free energy of activation per mole of solvent, (Δμ 0 # 1 ) and free energy of activation per mole of solute, (Δμ 0 # 2 ), were obtained by the application of transition-state theory. The refractive index was used to calculate molar refractive index, (R D ) of the solutes in different solvent mixtures. All these parameters are used to study the solute-solvent and solute-solute interactions in the mixtures used in the present investigation.

Application of Transition State Theory for Thermal Stability Prediction

Estimations of thermal hazards based on calorimetric experiments can be resource consuming. Therefore, reactive hazard predictions using computational techniques are an attractive option. Typically, prior to detailed experimentation, a screening test is performed on the set of potential reactive chemicals using a differential scanning calorimeter (DSC). The screening tests help to focus the resources on the more reactive systems. The onset temperature (To) and the energy of reaction (−ΔHrxn) are two important parameters obtained from a DSC run. Prediction of thermal stability requires the knowledge of both the thermodynamics and kinetics for the given system. In this paper, the energy of reaction (−ΔHrxn) is approximated by the maximum enthalpy of decomposition (as calculated by the CHETAH program) and transition state theory is employed to estimate the decomposition kinetics of aromatic nitro compounds. The activation energy is approximated as a fraction of the bond dissociation energy (BDE), calculated for the C−NO2 bond, at the B3P86 level of theory with the cc-pVDZ basis set. BDE values are also reported from the semiempirical AM1 theory. These quantum mechanical calculations are combined with an unsteady-state model for a batch reactor to predict onset temperatures for nineteen nitro compounds, which are compared with experimental values.

A multiscale study of the selective MOVPE of Al xGa 1− xAs in the presence of HCl

The selective deposition of Al x Ga 1− x As films on (1 0 0) substrates patterned with a SiN x mask is simulated at multiple length and time scales. First, gas-phase and surface kinetic schemes are developed to describe GaAs, AlAs and Al x Ga 1− x As deposition from TMGa, TMAl and AsH 3 in the presence of HCl. Unknown reaction kinetic constants are determined by quantum chemistry calculations of energy and structure followed by application of transition state theory. These estimated kinetic parameters and experimental values are then incorporated in finite element computations of flow, temperature, and species concentration fields in different MOVPE reactor configurations. The predicted local growth rates and gas-phase compositions are in good agreement with experimental data. The selective deposition on patterned substrates with different mask/feature ratios is also investigated with a feature scale model, coupled to the reactor scale model by imposing continuity of gas-phase concentrations and fluxes at the boundaries. The experimentally observed growth rate enhancement is reproduced quantitatively.