Combinatorial reaction searches on the PES using KinBot

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Русский язык для иностранных студентов учеб. пос. в 4-х т. Т. 2

В учебном пособии представлены все виды речевой деятельности студентов по изучению русского языка как иностранного, направленные на развитие речевого поведения, необходимого для эффективного обучения в украинских вузах, общения в академической и повседневной жизни. Задания и упражнения учебного пособия типичны для разных академических и социальных сфер и ситуаций. Организация содержания – четко структурирована, охватывает основные грамматические явления русского языка, ключевые слова по темам, автентичные тексты для чтения и обсуждения, аудирования, тексты для самостоятельной работы студентов. Пособие соответствует содержанию и требованиям Учебно-методического комплекса дисциплины «Русский язык как иностранный»

Diffusion Limited Kinetics In Reactive Systems

Proper representation of chemical kinetics is vital to understanding, modeling, and optimizing many important chemical processes. In liquid and surface phases, where diffusion is slow, the rate at which the reactants diffuse together limits the overall rate of many elementary reactions. Commonly, the textbook Smoluchowski theory is utilized to estimate effective rate coefficients in the liquid phase. On surfaces, modelers commonly resort to much more complex and expensive Kinetic Monte Carlo (KMC) simulations. Here we extend the Smoluchowski model to allow the diffusing species to undergo chemical reactions, and derive analytical formulae for the diffusion limited rate coefficients for 3D, 2D and 2D/3D interface cases. With these equations we are able to demonstrate that when species react faster than they diffuse they can react orders of magnitude faster than predicted by Smoluchowski theory, through what we term “the reactive transport effect.” We validate the derived steady state equations against particle Monte Carlo (PMC) simulations, KMC simulations and non-steady state solutions. Furthermore, using PMC and KMC simulations, we propose corrections that agree with all limits and the computed data for the 2D and 2D/3D interface steady state equations, accounting for unique limitations in the associated derived equations. Additionally, we derive equations to handle couplings between diffusion limited rate coefficients in reaction networks. We believe these equations should make it possible to run much more accurate mean-field simulations of liquids, surfaces, and liquid-surface interfaces accounting for diffusion limitations and the reactive transport effect

Advanced fuel chemistry for advanced engines.

Autoignition chemistry is central to predictive modeling of many advanced engine designs that combine high efficiency and low inherent pollutant emissions. This chemistry, and especially its pressure dependence, is poorly known for fuels derived from heavy petroleum and for biofuels, both of which are becoming increasingly prominent in the nation's fuel stream. We have investigated the pressure dependence of key ignition reactions for a series of molecules representative of non-traditional and alternative fuels. These investigations combined experimental characterization of hydroxyl radical production in well-controlled photolytically initiated oxidation and a hybrid modeling strategy that linked detailed quantum chemistry and computational kinetics of critical reactions with rate-equation models of the global chemical system. Comprehensive mechanisms for autoignition generally ignore the pressure dependence of branching fractions in the important alkyl + O{sub 2} reaction systems; however we have demonstrated that pressure-dependent 'formally direct' pathways persist at in-cylinder pressures

Directly measuring reaction kinetics of (center dot)QOOH - a crucial but elusive intermediate in hydrocarbon autoignition

Hydrocarbon autoignition has long been an area of intense fundamental chemical interest, and is a key technological process for emerging clean and efficient combustion strategies. Carbon-centered radicals containing an -OOH group, commonly denoted (center dot)QOOH radicals, are produced by isomerization of the alkylperoxy radicals that are formed in the first stages of oxidation. These (center dot)QOOH radicals are among the most critical species for modeling autoignition, as their reactions with O-2 are responsible for chain branching below 1000 K. Despite their importance, no (center dot)QOOH radicals have ever been observed by any means, and only computational and indirect experimental evidence has been available on their reactivity. Here, we directly produce a (center dot)QOOH radical, 2-hydroperoxy-2-methylprop-1-yl, and experimentally determine rate coefficients for its unimolecular decomposition and its association reaction with O-2. The results are supported by high-level theoretical kinetics calculations. Our experimental strategy opens up a new avenue to study the chemistry of (center dot)QOOH radicals in isolation

Pynta - An automated workflow for calculation of surface and gas-surface kinetics

Many important industrial processes rely on heterogeneous catalytic systems. However, given all possible catalysts and conditions of interest it is impractical to optimize most systems experimentally. Automatically generated microkinetic models can be used to efficiently consider many catalysts and conditions. However, these microkinetic models require accurate estimation of many thermochemical and kinetic parameters. Manually calculating these parameters is tedious and error prone involving many interconnected computations. We present Pynta, a workflow software for automating the calculation of surface and gas-surface reactions. Pynta takes the reactants, products and atom maps for the reactions of interest, generates sets of initial guesses for all species and saddle points, runs all optimizations, frequency, and IRC calculations and computes the associated thermochemistry and rate coefficients. It is able to consider all unique adsorption configurations for both adsorbates and saddle points allowing it to handle high index surfaces and bidentate species. Pynta implements a new saddle point guess generation method called harmonically forced saddle point searching (HFSP). HFSP defines harmonic potentials based on the optimized adsorbate geometries and which bonds are breaking and forming that allow initial placements to be optimized using the GFN1-xTB semiempirical method to create reliable saddle point guesses. This method is reaction class agnostic and fast, allowing Pynta to consider all possible adsorbate site placements efficiently. We demonstrate Pynta on 11 diverse reactions involving monodenate, bidentate and gas-phase species, many distinct reaction classes and both a low and a high index facet of Cu. Our results suggest that it is very important to consider reactions between adsorbates adsorbed in all unique configurations for inter-adsorbate group transfers and reactions on high index surfaces

Formation of Organic Acids and Carbonyl Compounds in n-Butane Oxidation via gamma-Ketohydroperoxide Decomposition

A crucial chain-branching step in autoignition is the decomposition of ketohydroperoxides (KHP) to form an oxy radical and OH. Other pathways compete with chain-branching, such as "Korcek" dissociation of gamma-KHP to a carbonyl and an acid. Here we characterize the formation of a gamma-KHP and its decomposition to formic acid+acetone products from observations of n-butane oxidation in two complementary experiments. In jet-stirred reactor measurements, KHP is observed above 590 K. The KHP concentration decreases with increasing temperature, whereas formic acid and acetone products increase. Observation of characteristic isotopologs acetone-d(3) and formic acid-d(0) in the oxidation of CH3CD2CD2CH3 is consistent with a Korcek mechanism. In laser-initiated oxidation experiments of n-butane, formic acid and acetone are produced on the timescale of KHP removal. Modelling the time-resolved production of formic acid provides an estimated upper limit of 2 s(-1) for the rate coefficient of KHP decomposition to formic acid+acetone.Peer reviewe