This article critically compares the efficacy of three algorithms, namely Alternating Least-squares Multi Curve Resolution (ALS-MCR), Hard Modeling Alternating Least-squares (HM-ALS), and classical Hard Modeling Multi Curve Resolution (HM-MCR) in finding the true values of rate constants associated with a kinetic model. Simulated experiments on the simple system () indicate that soft-modeling ALS-MRC methodology, which is subject only to linear constraints, does not ensure that experimental responses are correctly deconvolved, thus preventing further calculations to determine the true rate constants. Inclusion of the kinetic model in the ALS scheme, which gives rise to the HM-ALS methodology, was found to yield a correct assessment of the rate coefficients but had a large computational cost. Numerical experiments employing a more complex model () were also carried out, mainly to evaluate strategies for performing efficient searches on multidimensional multimodal least-squares surfaces using HM-ALS and HM-MCR. This study again revealed the efficiency and reliability of classical HM-MCR methods. Results from simulations were corroborated by analysis of data from an experimental study of chromate reduction by hydrogen peroxide; the mechanism of which is similar in complexity to those considered in simulations. The present work suggests that HM-MCR algorithms implementing a multiminimum search strategy are the method of choice for analyzing two-dimensional kinetic data.

A comprehensive and hierarchical optimization of a joint hydrogen and syngas combustion mechanism has been carried out. The Kéromnès et al. (*Combust Flame*, 2013, 160, 995–1011) mechanism for syngas combustion was updated with our recently optimized hydrogen combustion mechanism (Varga et al., *Proc Combust Inst*, 2015, 35, 589–596) and optimized using a comprehensive set of direct and indirect experimental data relevant to hydrogen and syngas combustion. The collection of experimental data consisted of ignition measurements in shock tubes and rapid compression machines, burning velocity measurements, and species profiles measured using shock tubes, flow reactors, and jet-stirred reactors. The experimental conditions covered wide ranges of temperatures (800–2500 K), pressures (0.5–50 bar), equivalence ratios (*ϕ* = 0.3–5.0), and C/H ratios (0–3). In total, 48 Arrhenius parameters and 5 third-body collision efficiency parameters of 18 elementary reactions were optimized using these experimental data. A large number of directly measured rate coefficient values belonging to 15 of the reaction steps were also utilized. The optimization has resulted in a H_{2}/CO combustion mechanism, which is applicable to a wide range of conditions. Moreover, new recommended rate parameters with their covariance matrix and temperature-dependent uncertainty ranges of the optimized rate coefficients are provided. The optimized mechanism was compared to 19 recent hydrogen and syngas combustion mechanisms and is shown to provide the best reproduction of the experimental data.

A detailed reaction mechanism for ethanol combustion was developed for describing ignition, flame propagation, and species concentration profiles with high accuracy. Starting from a modified version of the ethanol combustion mechanism of Saxena and Williams (*Proc. Combust. Inst*. 2007, 31, 1149–1156) and adopting the H_{2}/CO base chemistry from the joint optimized hydrogen and syngas combustion mechanism of Varga et al. (*Int. J. Chem. Kinet*. 2016, in press), an optimization of 54 Arrhenius parameters of 16 important elementary C_{1}/C_{2} reactions was performed using several thousand direct and indirect measurement data points as well as the results of theoretical determinations of reaction rate coefficients. The final optimized mechanism was compared to 16 reaction mechanisms that have been used for the simulation of ethanol combustion with respect to the accuracy in reproducing the available experimental data, including measurements of ignition delay times in shock tubes (444 data points in 39 data sets) and rapid compression machines (20/3), laminar burning velocity measurements (1011/124), and species profiles measured using flow reactors (1750/23), jet-stirred reactors (398/6) and shock tubes (8871/14). In addition to providing best fitted values for 54 Arrhenius parameters, the covariance matrix of the optimized parameters was calculated, which provides a description of the temperature-dependent ranges of uncertainty for each of the optimized rate coefficients.

The rate coefficients of the gas-phase reactions CH_{2}OO + CH_{3}COCH_{3} and CH_{2}OO + CH_{3}CHO have been experimentally determined from 298–500 K and 4–50 Torr using pulsed laser photolysis with multiple-pass UV absorption at 375 nm, and products were detected using photoionization mass spectrometry at 10.5 eV. The CH_{2}OO + CH_{3}CHO reaction's rate coefficient is ∼4 times faster over the temperature 298–500 K range studied here. Both reactions have negative temperature dependence. The *T* dependence of both reactions was captured in simple Arrhenius expressions:

The rate of the reactions of CH_{2}OO with carbonyl compounds at room temperature is two orders of magnitude higher than that reported previously for the reaction with alkenes, but the *A* factors are of the same order of magnitude. Theoretical analysis of the entrance channel reveals that the inner 1,3-cycloaddition transition state is rate limiting at normal temperatures. Predicted rate-coefficients (RCCSD(T)-F12a/cc-pVTZ-F12//B3LYP/MG3S level of theory) in the low-pressure limit accurately reproduce the experimentally observed temperature dependence. The calculations only qualitatively reproduce the *A* factors and the relative reactivity between CH_{3}CHO and CH_{3}COCH_{3}. The rate coefficients are weakly pressure dependent, within the uncertainties of the current measurements. The predicted major products are not detectable with our photoionization source, but heavier species yielding ions with masses *m*/*z* = 104 and 89 are observed as products from the reaction of CH_{2}OO with CH_{3}COCH_{3}. The yield of *m*/*z* = 89 exhibits positive pressure dependence that appears to have already reached a high-pressure limit by 25 Torr.

In this study, the photocatalytic degradation of oxytetracycline (OTC) in aqueous solutions has been studied under different conditions such as initial pollutant concentrations, amount of catalyst, and pH of the solution. Experimental results showed that photocatalysis was clearly the predominant process in the pollutant degradation, since OTC adsorption on the catalyst and photolysis are negligible. The optimal TiO_{2} concentration for OTC degradation was found to be 1.0 g/L. The apparent rate constant decreased, and the initial degradation rate increased with increasing initial OTC concentration with the other parameters kept unchanged. Subsequently, data obtained from photocatalytic degradation were used for training the artificial neural networks (ANN). The Levenberg–Marquardt algorithm, log sigmoid function in the hidden layer, and the linear activation function in the output layer were used. The optimized ANN structure was four neurons at the input layer, eighteen neurons at the hidden layer, and one neuron at the output layer. The application of 18 hidden neurons allowed to obtain the best values for *R*^{2} and the mean squared error, 0.99751 and 7.504e–04, respectively, showing the relevance of the training, and hence the network can be used for final prediction of photocatalytic degradation of OTC with suspended TiO_{2}.

The substitution of the chelating oxalate group by a group of nucleophiles, viz. thiourea (L_{1}), 2-thiouracil (L_{2}), diethyldithiocarbamate (L_{3}), dl-penicillamine (L_{4}), and thiosemicarbazide (L_{5}) was studied under pseudo–first-order conditions as a function of concentration and temperature using UV–vis spectrophotometry and stopped-flow technique. π-Accepting effects are often used to account for the unusual high lability of Pt(bipy) complexes. The complexes [Pt(dach)(oxalate)] (1) (dach = cis-1,2-diaminocyclohexane) and [Pt(bipy)(oxalate)] (2) (bipy = 2,2'-bipyridine) and substituted products were isolated and characterized by FTIR and ESI-MS spectroscopic analysis. The negative entropies of activation support a strong contribution from bond making in the transition state of the substitution processes.

Numerous mathematical tools intended to adjust rate constants employed in complex detailed kinetic models to make them consistent with multiple sets of experimental data have been reported in the literature. Application of such model optimization methods typically begins with the assignment of uncertainties in the absolute rate constants in a starting model, followed by variation of the rate constants within these uncertainty bounds to tune rate parameters to match model outputs to experimental observations. The present work examines the impact of including information on relative reaction rates in the optimization strategy, which is not typically done in current implementations. It is shown that where such rate constant data are available, the available parameter space changes dramatically due to the correlations inherent in such measurements. Relative rate constants are typically measured with greater relative accuracy than corresponding absolute rate constant measurements. This greater accuracy further reduces the available parameter space, which significantly affects the uncertainty in the model outcomes as a result of kinetic parameter uncertainties. We demonstrate this effect by considering a simple example case emulating an ignition event and show that use of relative rate measurements leads to a significantly smaller uncertainty in the output ignition delay time in comparison with results based on absolute measurements. This is true even though the same range of absolute rate constants is sampled in each case. Implications of the results with respect to the maintenance of physically realistic kinetics in optimized models are discussed, and suggestions are made for the path forward in the refinement of detailed kinetic models.

Linear free energy relationships (LFER) were applied to the kinetic data for the reaction of 5-substituted orotic acids, series **1**, with diazodiphenylmethane (DDM) in *N*,*N*–dimethylformamide and compared with results obtained for 2-substituted benzoic acids, series **2**. The correlation analysis of the kinetic data with *σ* substituent parameters was carried out using SSP (single substituent parameter) methods. From the sign and value of proportinality constant *ρ*, lower sensitivity to the substituent effect was obtained in series **1**, 0.876, than in the series **2**, 1.877. Evaluation of substituent “ortho-effect” was performed using the Charton model, which includes the steric substituent parameter, and Fujita and Nishioka's model, which describes the total ortho*-*effect as contribution of ordinary polar effect, the ortho*-*steric and ortho*-*polar effects. Results of correlations, obtained by using the Charton model, showed highest contribution of the polar effect, 0.861 vs. 2.101, whereas the steric effect is of lowest significance, 0.117 vs. 0.055, for series **1** and **2**, respectively. Also, a low negative value of coefficient with the steric effect, –0.08, obtained from the Fujita–Nishioka model indicated low steric effect, influencing a decrease of the reaction rate in series **1**. The structural and substituent effects were also studied by using the density functional theory method, and together with kinetic data, it gave a better insight into the influence of the effect of both geometry and substituent on the *π*−electron density shift induced reactivity of investigated acids.

Sodium hexafluorosilicate (Na_{2}SiF_{6}) powder has been used as a silicon source for formation of Si_{3}N_{4} coatings by the hybrid precursor system-chemical vapor deposition (HYSY-CVD) route. The quantitative effect of processing time, temperature, gas flow rate, and process atmosphere (N_{2} and N_{2}:5% NH_{3}) upon the fractional weight loss during the decomposition of Na_{2}SiF_{6} was studied using a standard L_{9} Taguchi experimental design and analysis of variance. The decomposition kinetics of Na_{2}SiF_{6}(s) was studied theoretically and experimentally in the temperature range of 550–650ºC by applying the shrinking core model. It was found that regardless of atmosphere type, the reaction order is *n* ≈ 0.12 and that a two-stage mixed mechanism consisting of chemical reaction and boundary layer gas transfer controls the decomposition rate. The determined fractional weight loss during Na_{2}SiF_{6} decomposition in nitrogen atmosphere is about 1.05–1.5 orders of magnitude greater than that in N_{2}:NH_{3}. The gas flow rate affects the dissociation activation energy, being of 121, 109, and 94 kJ/mol in N_{2} and of 140, 120, and 115 kJ/mol in N_{2}:NH_{3}, for the flow rates of 20, 60, and 100 cm^{3}/min, respectively, in both atmosphere types. A good agreement is observed by comparing experimental weight loss data with model predictions.