Theory Of Reactions Research Articles

Exploring the Unusual Reactivity of the Hydrated Electron with CO2.

Many questions remain about the reactions of the hydrated electron despite decades of study. Of particular note is that they do not appear to follow the Marcus theory of electron transfer reactions, a feature that is yet to be explained. To investigate these issues, we used ab initio molecular dynamics (AIMD) simulations to investigate one of the better studied reactions, the hydrated electron reduction of CO2. The rate constant for the hydrated electron-CO2 reaction complex to react to form CO2- is for the first time estimated from AIMD simulations. Results at 298 and 373 K show the rate constant is insensitive to temperature, consistent with the low measured activation energy for the reaction, and the implications of this behavior are examined. The sampling provided by the simulations yields insight into the reaction mechanism. The reaction is found to involve both solvent reorganization and changes in the carbon dioxide structure. The latter leads to significant vibrational excitation of the bending and symmetric stretch vibrations in the CO2- product, indicating the reaction is vibrationally nonadiabatic. The former is estimated from the calculation of an approximate collective solvent coordinate and the free energy in this coordinate is determined. These results indicate that AIMD simulations can reasonably estimate hydrated electron reaction activation energies and provide new insight into the mechanism that can help illuminate the features of this unusual chemistry.

Effect of mechanical energy input during mechanical crushing on the macrokinetics of the coal–oxygen reaction: A laboratory–scale study

Underground mining is usually simplified as a process of coal crushing and pulverization. However, this process is not purely physical. The mechanical energy input to this process also induces a mechanochemical effect. The specific impact of this effect on the macrokinetics of the coal–oxygen reaction (COR) has not been independently investigated, which motivates this work. Thermal analysis tests showed that mechanical energy input contributed to the strength of the COR and exhibited regularities in its impact on COR's kinetic parameters. Explanations for this were given based on mechanochemistry, free radicals chain reaction and quantum chemistry theories. A coal macromolecule model, influenced by mechanical energy input, was developed based on the typical Wiser model, and subsequent quantum mechanical calculations were conducted. It was found that mechanical energy input facilitated the breaking of specific chemical bonds in coal, redistributing the electrostatic potential and increasing the number of active sites within the coal molecule. Moreover, both the free radicals from bonds breaking and the remaining active structural sites exhibited an increasing trend in their electrified capacities. Different from the traditional physical pathway, this work refined the mechanism by which mechanical forces affect COR through the mechanochemical pathway.

Unearthing the Chicago Piles: A Monte Carlo perspective

The divergence of the Chicago Pile 1 (CP-1) on December 2nd, 1942, marks the birth of the nuclear age. Built under the West Stands of the Stagg Field in Chicago in slightly over two weeks, CP-1 was the first man-made nuclear reactor, conceived as a proof-of-principle physics experiment to demonstrate the feasibility of a self-sustained neutron chain reaction. The fuel consisted in a mixture of uranium oxide and metal uranium, with lumps of several sizes and shapes stacked within bricks of graphite used as moderator to form a cubic lattice. After only three months of operation, CP-1 was dismantled due to safety reasons and rebuilt at the Argonne Site in twenty-one days, under the name of Chicago Pile 2 (CP-2): the new pile had a longer life, contributing vastly to research on material science and nuclear reactor theory, and was finally decommissioned in 1954. Prompted by the eightieth anniversary of the Chicago Pile(s), in this talk we celebrate these astonishing scientific artifacts by building fully detailed three-dimensional digital twins of CP-1 and CP-2 using TRIPOLI-4®, the Monte Carlo code developed at CEA. Technological data for the models have been retrieved from published and unpublished documents of the Manhattan Project. We compare the simulation results to the available experimental measurements, encompassing the reactivity of the piles, the control rod worth, the kinetics parameters and several reactivity coefficients. For each, we examine the associated uncertainties due to missing or incomplete technological data as well as the bias due to nuclear data libraries.

The multichannel experimental and theoretical study of the 12C(18O,18F)12B single charge exchange reaction mechanism

The study of a network of nuclear reactions populated in the 18O + 12C collision is the main topic of the present paper. It was performed to test nuclear structure and reaction theories in describing the full reaction mechanism occurring in the (18O, 18F) single charge exchange nuclear reaction. From the experimental side, an 18O beam was produced at 275 MeV incident energy by the K800 superconducting cyclotron and the MAGNEX magnetic spectrometer was used at the Laboratori Nazionali del Sud of the Istituto Nazionale di Fisica Nucleare to momentum analyse the ejectiles produced in the nuclear reactions within the same experimental setup. From the theoretical side, the proposed approach consists of analysing the whole network of nuclear reactions in the framework of a unique comprehensive and coherent theoretical calculation. This holistic approach, applied both to the experimental and theoretical analysis, is the main feature and novelty of the work presented here.

Behavior of the continuum coupling correlation energy in the vicinity of the particle emission threshold - Gamow shell model study

The Gamow shell model provides the open quantum system formulation of nuclear shell model. In the coupled-channel representation, Gamow shell model provides the unified theory of nuclear structure and reactions which is well suited for the study of resonances and clustering. In this work, we apply this approach to study the continuum-coupling correlation energy for selected near-threshold states of 7Li, 7Be, using a translationally invariant Hamiltonian with an effective finite-range two-body interaction.

Formal theory of heavy ion double charge exchange reactions

The theory of heavy ion double charge exchange (DCE) reactions A(Z, N) → A(Z ± 2, N ∓ 2) is recapitulated emphasizing the role of Double Single Charge Exchange (DSCE) and pion-nucleon Majorana DCE (MDCE) reactions. DSCE reactions are of second–order distorted wave character, mediated by isovector nucleon-nucleon (NN) interactions. The DSCE response functions resemble the nuclear matrix elements (NME) of 2ν2β decay. The MDCE process proceeds by a dynamically generated effective rank-2 isotensor interaction, defined by off–shell pion–nucleon DCE scattering. In closure approximation pion potentials and two–nucleon correlations are obtained, similar to the neutrino potentials and the intranuclear exchange of Majorana neutrinos in 0ν2β Majorana double beta decay (MDBD).

Nuclear reactions as a tool to study the microscopic structure of pygmy and giant resonances

An advanced microscopic approach based on energy-density functional theory and the quasiparticle-phonon model has been used to study nuclear excitations up to giant dipole resonance energies. In addition, our nuclear structure model has been extended to include reaction theory. The theoretical spectral distributions compared with experimental data performed with different probes and techniques are able to provide us with information about the microscopic structure of the pygmy dipole resonance as well as its collectivity. Evaluations of electric dipole (E1) transition strengths and branching ratios at low energy reveal different properties of the nuclear excitations and the effect of quasi-continuum coupling. The present studies will support above-neutronthreshold γ experiments at ELI-NP targeting γ decays of giant and pygmy resonances, as well as studies on multi-step γ decays by low-lying states.

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(Invited) Non-Uniformly Polarized Reactive Electrochemical Membrane (REM) for Water Purification

A novel flow-through electrochemical technology (or termed reactive electrochemical membrane, REM) developed from porous electrode materials has recently attracted increasing attention globally in water purification and environment remediation. REM systems compress the boundary diffusion layer on the surface of the electrode via a combination of the convection of the solution and the constraint effect of the micro-pore structure, thus overcoming the mass transfer limitation in traditional flow-by systems. As a result, the kinetics of contaminant separation and conversion in a REM system increases by several to tens of times as compared with the flow-by systems. However, most existing studies are focused on the development of novel electrode materials, the evaluation of the removal efficiency and mechanism for contaminants, and the optimization of the treatment process of a REM system. In comparison, there is a gap in understanding the working principles of the REM electrodes. In contrast to the traditional flow-by system, the convective transport of the solution in the REM system drives the contaminants to the inside of the REM electrode, which activates the inner catalytic zone thereby. Because the electrode features the characteristics of non-uniform polarization, the given potential decays continuously along the depth of the REM electrode, thus causing a non-uniform distribution of the potential inside the REM electrode. As such, the zero-dimensional reaction theory of the electrode in traditional flow-by system (that is, the reaction mainly occurs on the surface of the electrode and is controlled by the potential) is no longer applicable to REM electrodes. It is therefore vital to revisit the reaction mechanism of the REM electrode. This Presentation therefore discusses the non-uniform polarization characteristics of the REM electrodes that are developed by loading catalytic layer on porous substrates. The main contents include: (1) REM electrode d emonstrates non-uniform oxidation characteristics: The key influencing factors ( i.e. , the pore structure of the REM electrode and the concentration of the electrolyte) and their principles of action to determine the reaction depth of a REM electrode have been identified, by employing (1) a developed mathematical model that could describe the spatial overpotential distribution as a function of depth in the REM electrode and (2) a visualization method to characterize the reactive depth of a REM electrode. (2) There is a structure-function relationship between the REM electrode pore structure and water purification efficiency : A series of SnO2-Sb-REMs with pore diameters in a range of 4.7 to 49.4 μm have been prepared to study the influence of the key factor ( i.e. , pore structure) on the transport-oxidation process of typical antibiotics. The REM electrode performance that could not constantly increase with a decrease in the pore diameter relates to the decreasing reactive depth of the electrode at a smaller pore diameter, which would lead to the compromise of the intrinsic kinetics of a REM electrode. (3) Direct electron transfer (DET) dominates the oxidation of antibiotics by using REM developed from porous substrates with a catalytic layer: The mechanism of typical antibiotics removal by employing SnO2-Sb-REM, β -PbO2-Sb-REM and Ti4O7-REM has been systematically investigated. The non-uniform oxidation characteristics of the REM electrode resulted in the DET rate being much higher than the yield of the hydroxyl radical (•OH), which was insignificantly affected by the electrode materials. The strong DET ability enabled the REM system to quickly and efficiently degrade antibiotics, which also imparted the REM system a stronger resistance to the background matrix (such as Cl–, HCO3 – and natural soluble organic matter).

Alternative method for determining leaf CO2 assimilation without gas exchange measurements: Performance, comparison and sensitivity analysis.

We present an alternative method to determine leaf CO2 assimilation rate (An ), eliminating the need for gas exchange measurements in proximal and remote sensing. This method combines the Farquhar-von Caemmerer-Berry photosynthesis model with mechanistic light reaction (MLR) theory and leaf energy balance (EB) analysis. The MLR theory estimates the actual electron transport rate (J) by leveraging chlorophyll fluorescence via pulse amplitude-modulated fluorometry for proximal sensing or sun-induced chlorophyll fluorescence measurements for remote sensing, along with spectral reflectance. The EB equation is used to directly estimate stomatal conductance from leaf temperature. In wheat and soybean, the MLR-EB model successfully estimated An variations, including midday depression, under various environmental and phenological conditions. Sensitivity analysis revealed that the leaf boundary layer conductance (gb ) played an equal, if not more, crucial role compared to the variables for J. This was primarily caused by the indirect influence of gb through the EB equation rather than its direct impact on convective CO2 exchange on the leaf. Although the MLR-EB model requires an accurate estimation of gb , it can potentially reduce uncertainties and enhance applicability in photosynthesis assessment when gas exchange measurements are unavailable.

В.И. Вернадский и новая парадигма

The main directions of V.I.Vernadsky's scientific activity during the period of the scientific revolution occurred at the end of the 19th and until the middle of the20th centuries are briefly listed. His decisive contribution to the initial research and practical application of the phenomenon of radioactivity and nuclear physics is shown. Based on the discovery of low-energy nuclear reactions more than 30 years ago, the development of Vernadsky's ideas about the role of radioactivity − the transformation of some chemical elements into other chemical elements − in geology, in the thermal balance of the Earth, in the prevalence of trace chemical elements is presented. Main provisions of the theory of low-energy nuclear reactions in condensed matter are listed: the threshold for excitation of the medium is indicated; shown is the possibility of generating a strong magnetic field in a unidirectional flow of electrons in a quasineutral plasma with the pairing of free electrons, and, subsequently, the pairing of atomic electrons into orthobosons with the latter forming a Bose-Einstein condensate, in which a new state of matter is formed − transatoms, which are combined, due to their ultra-strong magnetic fields, into nuclear transmolecule, in which multinuclear transmutation reactions occur with non-radioactive products; with the transformation of transmolecules into different sets of stable nuclei, subject to all conservation laws. In this case, the collective parameter that characterizes the quasi-equilibrium distribution of the mass numbers of isotopes – reaction products – is the “thermodynamic” coefficient of the energy content of the medium. Natural nucleosynthesis in the era of recombination of the Universe, which gave rise to the formation and development of organic chemical, and subsequently biochemical synthesis, is described. The development of Vernadsky's doctrine of the biosphere and noosphere of the Earth is supplemented by the concept of fractality of material, including biological structures with the further evolution of living matter, as well as by the concept of planetary nucleosynthesis. Starting from the idea of planetary nucleosynthesis, based on the mechanism of multinuclear quantum transitions of some atomic nuclei to others, a new doctrine of the geological development of the Earth and the foundations of quantum planetology were formulated, which explained the strict temporal cyclicity observed in the geological activity of the Earth associated with galactic jet energy flows. The issues discussed may become a basis for those directions in scientific research that will form a new paradigm, a new worldview.

안전의 4요소(4M)가 굴삭기 사고에 미치는 영향에 관한 연구

The construction industry is a disaster-prone industry, which accounts for about 50% of all industrial accidents, and the frequency of construction equipment use is increasing due to the large size and high-rise of structures in domestic construction projects, and the possibility of serious accidents is increasing, and in the event of a disaster, it is characterized by high intensity and high human and material losses. Despite existing research to solve these problems, construction machinery accidents have not decreased at construction sites, and this study aims to identify the cause of the accident by dividing the cause of the accident into four categories, examining the results, and contributing to the establishment of basic data to establish measures to prevent future construction accidents.
 This study is composed of five categories and I. In the introduction, research background, purpose, scope of research, and research method were presented, and II. In the theoretical consideration, H. W. Heinrich's 1959 theory of accident chain reaction, F. E. Fird's latest theory of disaster chain, construction machine accident cases, and prior research, III. The research method consisted of research questions, research hypotheses, operational definition of variables, composition of measurement tools, and surveys, IV. In the analysis results, general characteristic analysis, correlation, hypothesis verification, V. Through the conclusion, the test results were recorded and the direction setting of the limitations of the study and the impact of the four elements (4M) of future safety on excavator accidents was presented.
 <Table 7> shows how 'the four elements of safety (4M) affect excavator accidents at the construction site, which is a research problem, and the effects of Man (t=0.914, p=0.361) and Media (t=0.200, p=0.841) on excavators were not found to be significant. Accordingly, '[Hypothesis 1, 3] Human and environmental factors at construction sites will affect excavator accidents.' was rejected, and the effects of Machine (t=3.527, p<0.001), Management (t=5.988, p<0.001) on excavators have a significant impact, and accordingly, '[Hypothesis 2, 4] mechanical and management factors will affect excavator accidents at construction sites.'The research hypothesis 'was adopted.
 In the excavator accident, mechanical factors such as connection and mechanical device malfunction of the brought equipment and management factors such as safety inspections of equipment and surroundings before work are the most affected by the disaster impact. Accordingly, it is necessary to establish and implement measures through risk assessment during excavator work to identify industrial accident characteristics and social issues by industry and occupation to reduce accidents and deaths caused by industrial accidents, It is necessary to present policy directions and alternatives to prevent accidents and deaths more efficiently through multidimensional surveys and analysis of the risk of deaths and accidents in the area, and active research should be conducted.

Diffusion-Controlled Reactions: An Overview.

We review the milestones in the century-long development of the theory of diffusion-controlled reactions. Starting from the seminal work by von Smoluchowski, who recognized the importance of diffusion in chemical reactions, we discuss perfect and imperfect surface reactions, their microscopic origins, and the underlying mathematical framework. Single-molecule reaction schemes, anomalous bulk diffusions, reversible binding/unbinding kinetics, and many other extensions are presented. An alternative encounter-based approach to diffusion-controlled reactions is introduced, with emphasis on its advantages and potential applications. Some open problems and future perspectives are outlined.

Simultaneous identification of strong and weak interactions with Pauli energy, Pauli potential, Pauli force, and Pauli charge.

Strong and weak interatomic interactions in chemical and biological systems are ubiquitous, yet how to identify them on a unified theoretical foundation is still not well established. Recently, we proposed employing Pauli energy-based indexes, such as strong covalent interaction and bonding and noncovalent interaction indexes, in the framework of density functional theory for the purpose. In this work, we extend our previous theoretical work by directly employing Pauli energy, Pauli potential, Pauli force, and Pauli charge to simultaneously identify both strong covalent bonding and weak noncovalent interactions. Our results from this work elucidate that using their signature isosurfaces, we can identify different types of interactions, either strong or weak, including single, double, triple, and quadruple covalent bonds, ionic bond, metallic bond, hydrogen bonding, and van der Waals interaction. We also discovered strong linear correlations between Pauli energy derived quantities and different covalent bond orders. These qualitative and quantitative results from our present study solidify the viewpoint that a unified approach to simultaneously identify both strong and weak interactions is possible. In our view, this work signifies one step forward towards the goal of establishing a density-based theory of chemical reactivity in density functional theory.

Effect of Filling Interval Time on Mechanical Characteristics of Cemented Tailing Backfill.

In order to study the strength reduction caused by delamination, single-gap and double-gap specimens were made, and a uniaxial compressive strength (UCS) test was used to analyze the relationship between filling interval time (FIT) and UCS of single and double-spacing specimens. Based on the cement hydration reaction theory and damage mechanics, the influence mechanism of the FIT on backfill strength was studied. The test results show that the UCS of double-interval backfill is affected by two filling intervals at the same time, and the lower clearance has a greater influence on the strength of the backfill than the upper clearance. With the increase of FIT, the UCS of the filling body decreases gradually. The cementation effect of single and double fillings is negatively correlated with the FIT. Filling within 0-12 h has little effect on the strength of the filling body. On this basis, a mathematical model between damage increment and damage dissipated energy is established. Under the same stress condition, the larger the damage variable (D), the smaller the dissipated energy (G) required by the damage expansion of unit filling body. This study provides a reasonable reference for the design of the filling interval in mine fractional filling.

Michael addition reaction and its examples

Michael addition reaction refers to the conjugate addition reaction of carbocation to , -unsaturated aldehydes, ketones, carboxylic acids, esters, nitrile, nitro compounds, etc. The reaction is an essential organic reaction, and it is used in organic synthesis to grow carbon chains and synthesize organic compounds with various functional groups. As one of the most valuable organic synthesis reactions, it is one of the most common ways to construct carbon-carbon bonds. This paper analyzes the mechanisms and the theories of some common Michael addition reactions. It also includes an example of the research of Michael addition in recent years. In a recent study, a research team experimentally found a suitable catalyst to catalyze the Michael addition reaction on benzyl groups, and obtained the different performances of benzyl groups with different functional groups during addition. Cyclopentadienyl rhodium catalyst has excellent catalytic activity and selectivity for benzyl first, second, and third C/H bonds. The reaction can be compatible with halogen, ester, and amide functional groups.

Microscopic quantum mechanical Marcus theory for chemical reactions and its relationship to theButler‐Volmerequation used in redox flow battery analysis

AbstractThe vanadium redox flow battery has been intensively examined since the 1970s. What is missing is a connection between the current‐overpotential Butler‐Volmer equation, which provides an extremely helpful starting point for analytical and numerical studies, and microscopic quantum mechanical behavior at the atomic level. Such a connection will allow further advancements beyond the macroscopic, though very useful and insightful, modeling already done in the literature. Here we show rigorously the connection between the Butler‐Volmer transfer coefficients, and the Marcus Gibbs free energy quantum mechanical parameters, and develop the equation directly in terms of the quantum mechanical parameters.

Metastable structure II methane hydrate: A bridge to obtain high methane uptake in the presence of thermodynamic promoter

The addition of thermodynamic promoters is a promising and perhaps the only effective method to reduce hydrate formation conditions. However, this is achieved at the cost of the gas storage capacity reduction since the thermodynamic promoter will occupy some hydrate cages. To date, there is no effective method that can simultaneously limit this negative effect and obtain high water-to-hydrate conversion. In this work, we determine the methane (CH4) hydrate formation mechanism in the presence of a thermodynamics promoter, Cyclopentane (CP), and find that structure II (Str.II) CH4 hydrate, as a metastable intermediate structure of the reaction, plays a quite significant role in encapsulating CH4 molecules in some 51264 cages (Str.II hydrates) and facilitating structure I CH4 hydrate formation, thereby increasing gas uptake significantly. A CH4 uptake, as high as 141.21 mmol/molH2O, is obtained from this work. Relative to the acknowledged limit of CH4 uptake of Str.II hydrates formed commonly in the presence of same mole fractions of thermodynamics promoter (8(Promoter)·16(CH4)·136H2O)), the highest increase in CH4 uptake is up to 232.75 %. These results would stimulate the development of the hydrate reaction theory and provide a new direction for promoter design.

Quantum and anharmonic effects in non-adiabatic transition state theory.

Quantitative descriptions of non-adiabatic transition rates at intermediate temperatures are challenging due to the simultaneous importance of quantum and anharmonic effects. In this paper, the interplay between quantum effects-for motion across or along the seam of crossing-and anharmonicity in the seam potential is considered within the weak coupling limit. The well-known expression for quantized 1-D motion across the seam (i.e., tunneling) in the linear terms approximation is derived in the thermal domain using the Lagrangian formalism, which is then applied to the case when tunneling is distributed along the seam of crossing (treating motion along the seam classically). For high-frequency quantum modes, a vibrationally adiabatic (VA) approach is developed that introduces to the non-adiabatic rate constant a factor associated with high-frequency wavefunction overlap; this approach treats the high-frequency motion along the seam quantum mechanically. To test these methodologies, the reaction N2O ↔ N2 + O(3P) was chosen. CCSD(T)-F12b/cc-pVTZ-F12 explorations of the 3A'-1A' seam of N2O revealed that seam anharmonicity has a strong effect on the rate constant (a factor of ∼20 at 2000K). Several quantum effects were found to be significant at intermediate/lower temperatures, including the quantum N-N vibration that was coupled with seam anharmonicity using the VA approach. Finally, a 1-D approximation to non-adiabatic instanton theory is presented to estimate the validity limit of the linear terms model at low temperatures (∼250 K for N2O). We recommend that the assumptions built into many statistical theories for non-adiabatic reactions-harmonic behavior, classical motion, linear terms, and weak coupling-should be verified on a case-by-case basis.

Accurate dynamics from self-consistent memory in stochastic chemical reactions with small copy numbers

We present a method that captures the fluctuations beyond mean field in chemical reactions in the regime of small copy numbers and hence large fluctuations, using self-consistently determined memory: by integrating information from the past we can systematically improve our approximation for the dynamics of chemical reactions. This memory emerges from a perturbative treatment of the effective action of the Doi-Peliti field theory for chemical reactions. By dressing only the response functions and by the self-consistent replacement of bare responses by the dressed ones, we show how a very small class of diagrams contributes to this expansion, with clear physical interpretations. From these diagrams, a large sub-class can be further resummed to infinite order, resulting in a method that is stable even for large values of the expansion parameter or equivalently large reaction rates. We demonstrate this method and its accuracy on single and multi-species binary reactions across a range of reaction constant values.