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The physicochemical conditions of the siliconizing and boron–siliconizing processes of molybdenum-based alloys in a closed reaction space in an environment of chlorine and fluorine at reduced pressure were studied. Theoretical calculations of the equilibrium composition of systems with the participation of silicon, boron, molybdenum, nitrogen, oxygen, chlorine, and fluorine were carried out, which made it possible to determine the influence of process parameters (temperature, composition of the reaction medium) on the probable phase composition of the obtained coatings. Based on thermodynamic calculations, the composition and rational consumption of the initial powders and the temperature intervals of the chemical heat treatment (CHT) during the complex saturation of molybdenum-based alloys with silicon and boron were modeled. It was established that it is advisable to use chlorine as an activator, which leads to the formation of molybdenum chlorides MoCl4 and MoCl3 in the composition of the gas phase and can indicate the flow of exchange reactions between chlorides and the matrix of the processed material in the reaction space. The rational saturation temperature of alloys based on molybdenum with silicon and boron is determined—1100–1250 °C. The possibility of the existence of condensed phases MoSi2, MoB2.15, B6Si, MoB1.65, and MoB is shown. [ABSTRACT FROM AUTHOR]

The package of the applied programs with base of the thermodynamic data is used and the theoretical analysis of physical and chemical conditions of complex- saturation carbon steel by silicon and chrome in medium of chlorine in the closed reactionary space is carried out at the lowered pressure of a gas phase. Simultaneous saturation of steel 40 with chrome and silicon in chlorine atmosphere for 6 hours at a temperature of 1323 K and a pressure of 102 Pa of the gas phase is carried out in this work. By means of the x-ray diffraction studies, it is found that, under the assumed conditions of saturation on the steel 40 surface, diffusion layer with thickness of 100-110 µm is formed, which corresponds to the phase of the corresponding chromium carbides Cr23C6 and Cr7C3 doped with silicon, and a solid solution of chromium and silicon in α-iron. The corrosion studies carried out in this work show that chromosilicide coatings applied onto carbon steel 40 are less stable in solutions of 10% hydrochloric and sulphuric acids, and the most stable in solutions of nitric acid. [ABSTRACT FROM AUTHOR]

Step‐scan Fourier‐transform infrared spectroscopy (ssFTIR) simultaneously provides the spectroscopic and kinetic information of a given reaction. ssFTIR has been extensively employed to acquire the transient absorption and emission spectra in gas phase for identifying unstable species, for example, various Criegee intermediates, and elucidating the dynamics and kinetics of the reaction, such as the molecular elimination dynamics of haloalkenes and the bimolecular reactions involving chlorine atoms and singlet oxygen atoms. In addition to gaseous studies, ssFTIR has been also utilized to record the time‐resolved difference spectra of the photochemical reactions in condensed phases, such as the photolysis of metal–ligand complexes, photocycles of the retinal proteins, coordination capability of solvents to unstable transient species, chemical reactions of atmosphere‐related molecules in aqua, and the exciplex dynamics of organic light emitting materials. Moreover, my group has pioneered the recording of the transient thermal infrared emission of gold nanostructures upon photoexcitation. The experimental setups and the working principles for probing the time‐resolved infrared absorption and emission in condensed phases will be revealed and a number of studies on chemical, biological, and materials systems will be described. These reported results demonstrate that ssFTIR is a versatile tool for exploring the properties of novel materials and photoreactions in condensed phases. [ABSTRACT FROM AUTHOR]

We begin by reviewing the early developments in the synthesis of high-spin organic molecules and the simultaneous rationalization of the ground states of high spin. A number of chemists contributed, most notably Gomberg and Hückel, and theoreticians like Coulson, Rushbrooke, Longuet-Higgins, McConnell, Hoffmann etc. The subject achieved maturity after 1970. Theoretical advances were made. Methods of calculations such as multi-configuration self-consistent-field, coupled cluster, density functional, and broken-symmetry methodologies prospered. These were in turn increasingly used in magnetic studies on organic species. Armed with the concepts, theory, and calculational methodologies, both experimental and theoretical researches involved the design of fascinating magnetic organic molecules, especially since 2000. The effects of varying chemical structures, aromaticity, presence of heteroatoms, effects of hydrogen bonding and tautomerism, stereochemical aspects, and the formation of polymers, extended systems and crystals were all considered. A multitude of applications was found in the form of single molecule magnets, photomagnets and photomagnetic switches, spin cross-over, excitation and redox process assisted magnetic activation, spintronics, and so on. A spectacular growth in applications has been witnessed in the last decade. It has been accompanied by speculative and predictive advances in theory and computational investigation.

This article investigates the radiolysis of a mixture of nitric acid with water (HNO3:H2O) at 16 K in high-vacuum (residual pressure < 10−6 mbar). A nitric acid-water ice film was exposed to 40 MeV 58Ni11+ ion beam in a heavy ion accelerator facility in France. For this astrochemically- and atmospherically-relevant ice mixture of nitric acid and water, we analyze the possible formation and destruction processes of N–O bearing species, thus providing spectroscopic data in the infrared (IR) region for theoretical, laboratory and observational future studies. The irradiation synthetized 18 species which were posteriorly examined by infrared spectroscopy: N2O, NH3, NO, NO2 and H x N y O z molecules, such as hidroxylamine (NH2OH), nitrous acid (HONO) as well as other species with bonding N–O, N–H and H–O–N converting surface-adsorbed nitrogen oxides into astrochemically active NO x. The interaction of HNO3 and H2O originates H–N–O molecular complexes, which were investigated as particular cases of the hydrogen-bonded species formed by a more electronegative atom (N or O) interacts intra or intermolecularly with a donor atom (N or O) and observed in the interstellar medium with higher quantities or great abundances. The HNO3 and H2O destruction cross sections have been determined to be 8.5 × 10−13 and 1.2 × 10−13 cm2, respectively, for the mentioned experimental conditions. [ABSTRACT FROM AUTHOR]

The physicochemical conditions of the siliconizing and boron–siliconizing processes of molybdenum-based alloys in a closed reaction space in an environment of chlorine and fluorine at reduced pressure were studied. Theoretical calculations of the equilibrium composition of systems with the participation of silicon, boron, molybdenum, nitrogen, oxygen, chlorine, and fluorine were carried out, which made it possible to determine the influence of process parameters (temperature, composition of the reaction medium) on the probable phase composition of the obtained coatings. Based on thermodynamic calculations, the composition and rational consumption of the initial powders and the temperature intervals of the chemical heat treatment (CHT) during the complex saturation of molybdenum-based alloys with silicon and boron were modeled. It was established that it is advisable to use chlorine as an activator, which leads to the formation of molybdenum chlorides MoCl4 and MoCl3 in the composition of the gas phase and can indicate the flow of exchange reactions between chlorides and the matrix of the processed material in the reaction space. The rational saturation temperature of alloys based on molybdenum with silicon and boron is determined—1100–1250 °C. The possibility of the existence of condensed phases MoSi2, MoB2.15, B6Si, MoB1.65, and MoB is shown.

Flame retardant poly(ethylene terephthalate) (FRPET) fabrics are widely used in daily life. However, the meltdrop and visible smoke produced during combustion significantly limit its further application. This study proposes a simple but effective method of fiber‐blending to improve the above shortcomings. On the basis of synergistic flame retardancy of nitrogen and phosphorus, the FRPET was blended with flame retardant viscose (FRV) and intrinsic nitrogen‐containing flame retardant fibers (NIFRFs), to prepare the binary and ternary blended FRPET samples labeled as NIFRF/FRPET and FRV/NIFRF/FRPET, respectively. The limiting oxygen index and cone calorimeter test show that the ternary‐blending could effectively suppress the combustion of FRPET fiber composite. The smoke density test and UL‐94 vertical combustion test indicate that ternary‐blending could better improve the meltdrop characteristics and smoke suppression property than binary‐blending. Among all samples, FRV/PMIA/FRPET (1:4:5) owns the highest LOI of 32.6% and lowest smoke density of 61.37. The investigation of residual char utilizing scanning electron microscopy, the X‐ray photoelectron spectroscopy and the Laser Raman spectroscopy demonstrates that the FRPET meltdrop would adhere to the surface of component fibers to avoid droplets. Besides, fiber‐blending could increase the yield and degree of graphitization of residual char, which is conducive to improving samples' flame retardancy through the condensed phase. This work may provide a workable strategy to expand the application areas of FRPET fabrics. [ABSTRACT FROM AUTHOR]

In this study, thermodynamic modelling of the process of thermal destruction of oil-contaminated soil of Ozenmunaigas JSC, which includes compounds such as carbon, silicon, aluminum, iron, calcium, magnesium, sodium, potassium, chromium, phosphorus, manganese, copper, titanium, molybdenum, nickel, vanadium, and water, was carried out. The physicochemical and thermodynamic parameters of the complex system were calculated at P=0.1 MPa, T=598-3000 K. The concentration distribution of components, particles, and condensed phases in the gas phase has been established. In the process of thermal destruction of oil-contaminated soil, the formation of condensed phases was as follows: SiO2(c), Al2O3(c), AlO3H3(c), Cu(c), Cu2O(c), FeO(c), Fe2O3(c), Fe3O4(c), Fe2SiO4(c), NiO(c), MnO(c), Mn3O4(c), MnO2H2(c), Cr2O3(c), MoO2(c), V2O3(c), V2O4(c), TiO2(c), MgSiO3(c), Mg2SiO4(c), MgTi2O5(c), Ca3P2O8(c), Mg2SiO4(c), MgTi2O5(c), Ca3P2O8(c), CaCO3(c), CaSiO3(c), CaTiO3(c), Na2Si2O5(c), K2Si4O9(c). At the same time, the amount of condensed calcium silicate CaSiO3(c) was significant and amounted to 3.2 mol/kg, which is due to the initial standard content of oxides of the type (g/kg): SiO2-473,7, CaO-181,5 in oil-contaminated soil. The formation of various types of condensed phases (from 10-30 to 10-4 mol/kg) during thermal degradation can help reduce the synergism and toxicity of metal particles in oil-contaminated soils. In the process of thermal destruction of oil-contaminated soil, its carbon-containing components (mg/kg: C12-6,27; C13-10,98; C14-15,69; C15-18,82; C16-23,52; C17-31,37; C18-27,80; C19-17,25; C20-29,80) were mainly converted into oxide, carbon dioxide, and water, and thereby neutralized the organic mass of the soil. [ABSTRACT FROM AUTHOR]

Photoluminescent liquid-crystalline (PLLC) molecules, which can easily tune the PL behavior through the crystal (Cry)–LC phase transition, have attracted significant attention. Previously, we have demonstrated that the incorporation of a semifluoroalkoxy chain into π-conjugated mesogen is a promising approach for developing PLLC molecules with PL and SmA LC characteristics. We focused on the LC and PL characteristics of the molecules induced by the semifluoroalkoxy chain and fluorinated tolanes in the condensed phase. In this study, we developed cyano- or ethoxycarbonyl-terminated donor-π-acceptor-type fluorinated tolanes containing a semifluoroalkoxy flexible chain. The cyano-terminated fluorinated tolanes exhibited intense light-blue photoluminescence in the crystalline phase and did not exhibit any LC phase. In contrast, blue photoluminescence in the ethoxycarbonyl-terminated analogs was slightly weak; however, they exhibited Cry–SmA phase transition during the heating and cooling processes. The PL intensity of the ethoxycarbonyl-terminated fluorinated tolanes significantly decreased in the SmA phase; however, their PL colors changed during the Cry–SmA phase transition. This indicates that the developed tolanes are promising temperature-dependent PL materials, such as PL thermosensors or PL thermometers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Unsorted PET in waste thermochemical recycling forms char and alters product yields. • First quantitative kinetic model for PET condensed-phase thermal degradation. • Critical evaluation of molecular and radical pathways by gas-phase analogies. • Experimental investigation by GCxGC-MS/FID, RGA, TGA, and elemental analyses. • Model validation on mass-loss profiles, gas and tar distribution, char composition. In a circular economy perspective, plastic waste (PW) is a valuable source of chemicals and energy vectors. Understanding the effect of poly(ethylene terephthalate) (PET) in thermochemical valorisation of complex and contaminated PW mixtures requires definition of suitable kinetic models. This work proposes a condensed-phase semi-detailed kinetic model for PET pyrolysis based on a consolidated functional group approach already validated for other polymers. The reaction network is built considering studies on thermal degradation of PET, model compounds, and small gas-phase esters. Reaction pathways proposed in the scientific literature are critically assessed through analogy with high accuracy gas-phase calculation and are complemented by new proposed pathways. The resulting model couples molecular and radical mechanism and consists of 85 gas and liquid species with 700 liquid-phase reactions, being suitable for CFD simulations of PW pyrolysis upon further reduction. This work also presents new experimental data including TG analysis coupled with GC × GC speciation measurements and elemental characterization of the solid residue. The model is validated by comparison with the new experimental data and a comprehensive set of literature data in terms of characteristic degradation times and detailed product yields. The present work expands the relevant data available for chemistry models development and extends the CRECK kinetic framework for thermochemical recycling of PW mixtures. The proposed kinetic model is attached as Supplementary material and freely available as an open GitHub repository. [ABSTRACT FROM AUTHOR]

We present a simple method to numerically evaluate different thermodynamic quantities of non-interacting Bose gas confined in a 3D box. This method only requires the knowledge of statistical mechanics and numerical integration at the undergraduate level. Thus the proposed technique is very much appropriate for the undergraduate class. [ABSTRACT FROM AUTHOR]

Exothermic reactions between oxophilic metals and transition/ post transition metal-oxides have been well documented owing to their fast reaction time scales (≈ 10 μs). This article examines the extent of reaction in nano-aluminum based thermite systems through a forensic inspection of the products formed during reaction. Three nanothermite systems (Al/CuO, Al/Bi2O3 and Al/WO3) were selected owing to their diverse combustion characteristics thereby providing sufficient generality and breadth to the analysis. Microgram quantities of the sample were coated onto a fine platinum wire, which was resistively heated at high heating rates (≈ 105 K/s) to ignite the sample. The subsequent products were captured/quenched very rapidly (≈ 500 μs) in order to preserve the chemistry/morphology during initiation and subsequent reaction and were quantitatively analyzed using electron microscopy (EM), focused ion beam (FIB) cross-sectioning followed by energy dispersive X-ray spectroscopy (EDX). Elemental examination of the cross-section of the quenched particles show oxygen predominantly localized in the regions containing aluminum, implying the occurrence of redox reaction. The Al/CuO system, which has simultaneous gaseous oxygen release and ignition (TIgnition ≈ TOxygen Release ), shows substantially lower oxygen content within the product particles as opposed to Al/Bi2O3 and Al/WO3 thermites, which are postulated to undergo a condensed phase reaction (TIgnition << TOxygen Release ). An effective Al:O composition for the interior section was obtained for all the mixtures, with the smaller particles generally showing higher oxygen content than the larger ones. The observed results were further corroborated with the reaction temperature, obtained using a high-speed spectro-pyrometer, and bomb calorimetry conducted on larger samples (≈ 15 mg). The results suggest that thermites that produce sufficient amounts of gaseous products generate smaller product particles and achieve higher extents of completion.

The molecular perovskite energetic materials (H2dabco)[NH4(ClO4)3] (DAP-4, H2dabco2+ = 1,4-diazabicyclo[2.2.2]octane-1,4-diium), limits its separate application in explosives duo to the severe negative oxygen balance. Therefore, it is of great significance to study the thermal decomposition performance of DAP-4 in the presence of AP oxidant. In this work, the differential scanning calorimetry-thermogravimetry-mass spectrometry-fourier transform infrared spectroscopy (DSC-TG-MS-FTIR) coupling technique, thermal decomposition kinetics, and in-situ FTIR method were used to analyze the thermal decomposition characteristics, and the variation of condensed phase characteristic groups of DAP-4 and the DAP-4/AP mixtures. The results show that AP has negligible effect on thermal decomposition temperature of DAP-4 but can prolong the total decomposition time of DAP-4 by 5.55 min. In addition, thermal decomposition of AP and DAP-4 in the mixture is independent of each other, and the thermal decomposition mechanism of DAP-4/AP mixtures is more complicated than that of DAP-4 alone. Thermal decomposition of DAP-4/AP mixture firstly experiences decomposition of AP at low temperature, the inside crystal transformation of DAP-4, the H+ transfer, and then cage skeleton collapse-induced redox reaction to generate large amount of heat which can shift forward the high-temperature decomposition peak of AP.

Naphthalene, the most prevalent and smallest member of the Polycyclic Aromatic Hydrocarbons (PAHs) family, has garnered significant scientific attention for its harmful environmental impacts and those of its degradation products. In this work, we comprehensively recharacterized the gas-phase reaction of naphthalene with OH radicals in a wide range of conditions (T = 200–2000 K & P = 0.76–7600 Torr), covering both atmospheric and combustion chemistry. Within the Rice–Ramsperger–Kassel–Marcus (RRKM)-based master equation framework, the detailed kinetic model was constructed on the potential energy surface explored at the ROCBS-QB3//M06–2X/aug-cc-pVTZ level of theory. Our model not only helps to resolve the existing large discrepancy (up to ∼1000 times) among the previously reported rate constants but also reveals mechanistic insights, including time-resolved species profiles and product distribution, for naphthalene transformation. It is shown that although naphthalene cannot be considered a persistent organic compound (POP) due to its rapid reaction with OH radicals, its chemical conversion can generate harmful substances such as O 3 and carcinogenic derivatives. Also, the detailed conversion of naphthalene in water was investigated for the first time, revealing that naphthalene and its important degradation products pose a significant danger to aquatic life as hazardous pollutants. [Display omitted] [ABSTRACT FROM AUTHOR]

• Phenomenon of variable activation energy has many practical uses as follows. • Evaluating effective activation energies, preexponential factors and rate constants. • Generating mechanistic hypotheses and forecasting kinetics. • Testing validity of assumed temperature dependencies. • Determining parameters of kinetic models. In this review article, the author briefly shares his personal experience of exploring the phenomenon of variable activation energy. Isoconversional methods frequently yield variable activation energy, E α , which depends on conversion, α. It is emphasized that isoconversional kinetic analysis should not be limited to simply evaluating and reporting the E α dependencies. Deeper insights into the thermal kinetics are gained by exploiting the intrinsic properties of the E α dependencies. These properties can be defined as diagnostic, exploratory, predictive, modelistic, and intermediary. Thanks to them one can generate mechanistic hypotheses, test the validity of assumed temperature dependencies of the process rates, forecast the kinetics beyond experimental conditions, determine parameters of kinetic models, and evaluate the preexponential factors and reaction rate constants. The article provides a practical overview of these properties of the E α dependencies and illustrates their usage by instructive examples. [Display omitted] [ABSTRACT FROM AUTHOR]

Condensed phase reactions have recently attracted increased interest, but principles for efficiently screening and designing catalyst materials through computations are lacking. In this study, we examine the applicability of energy correlations between adsorbed surface species, which have been instrumental in accelerating the computational design of catalyst materials in gas‐phase contexts, in various representations of a condensed phase reaction environment. We perform detailed density functional theory calculations of the adsorption of atomic and molecular species in the presence of various representations of solvent species. Our results show that the well‐known scaling in the gas phase context is preserved, with scaling slopes unaffected by the adsorbate‐liquid interactions. Moreover, these results hold when changing surface structure, solvent identity, and even in highly disordered environments. We envision the establishment of an energy scaling framework for condensed phase reactions to accelerate catalyst discovery and design in those contexts. [ABSTRACT FROM AUTHOR]

The kinetic parameters of condensed phase global reaction are required to calculate temporal and energetic characteristics of the ignition and combustion of energetic materials (EMs). The heating rate of EM in these processes exceeds 1000 K/s and therefore the kinetic data obtained via using classical thermal analysis methods with heating rate of 1–50 K/min may not provide the processes adequate description. A solution to the problem was suggested more than 50 years ago by Merzhanov who noticed a possibility to determine required kinetic parameters from the EM experimental ignition delays. However, mathematical background and justification for this approach has not been performed. It is commonly assumed that the approach yields the true kinetics at high heating rates of EMs. The present work aims to verify the validity of Merzhanov's approach. Numerical calculations were performed using transient mathematical models of the EM ignition and the results of virtual ignition experiments were processed using Merzhanov's ignition criterion. The deliverables were the values of kinetic parameters that substantially differ from those used as input data in numerical calculations. The paper concludes about necessity of elaborating mathematically substantiated techniques for determining kinetic parameters of global exothermic condensed-phase reaction via using the EM ignition delays. [ABSTRACT FROM AUTHOR]

A method is developed for secondary data processing of the results of simulation of two-phase flow in an afterburner with a complex geometry. This method offers a prediction for mixing process efficiency (quality estimate) and combustion efficiency in an afterburner of a power plant. The opportunities of this method were demonstrated at the example of simulation of mixing the two-phase fuel with air in the afterburner of a model power plant with gas generation outlay. The paper presents a mathematical model for studied processes and the simulation results. The fuel was the gasification products (GP) of a high-energy composition (a mixture of gaseous and condensed phases). An algorithm was applied for processing the mathematical simulation results: the output is the evaluation of mixing between GP condensed phase and air flow. The parametric study offers the dependencies for size distributions of GP particles in the afterburner cross sections. The limiting values for GP combustion efficiency in the afterburner were evaluated from analysis of GP flow (gas and condensed phases) mixing with air flow. Simulation gives the data on the influence of injection configuration and GP condensed phase dispersion profile on the mixing efficiency in the afterburner. The results of study can be useful in recommendations for gaining on the cycle efficiency in novel propulsion plants. [ABSTRACT FROM AUTHOR]

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Reliable simulations of molecules in condensed phase require the combination of an accurate quantum mechanical method for the core region, and a realistic model to describe the interaction with the environment. Additionally, this combination should not significantly increase the computational cost of the calculation compared to the corresponding in vacuo case. In this review, we describe the combination of methods based on coupled cluster (CC) theory with polarizable classical models for the environment. We use the polarizable continuum model (PCM) of solvation to discuss the equations, but we also show how the same theoretical framework can be extended to polarizable force fields. The theory is developed within the perturbation theory energy and singles‐T density (PTES) scheme, where the environmental response is computed with the CC single excitation amplitudes as an approximation for the full one‐particle reduced density. The CC‐PTES combination provides the best compromise between accuracy and computational effort for CC calculations in condensed phase, because it includes the response of the environment to the correlation density at the same computational cost of in vacuo CC. We discuss a number of numerical applications for ground and excited state properties, based on the implementation of CC‐PTES with single and double excitations (CCSD‐PTES), which show the reliability and computational efficiency of the method in reproducing experimental or full‐CC data. This article is characterized under:Electronic Structure Theory > Ab Initio Electronic Structure MethodsElectronic Structure Theory > Combined QM/MM MethodsSoftware > Quantum Chemistry [ABSTRACT FROM AUTHOR]

Copper‐based catalyst was applied in the condensed diester hydrogenation with unexpected high selectivity (∼100 %) to 1,6‐hexanediol. On basis of the mass transfer analysis and kinetics results, the reaction rate of the condensed diester hydrogenation was deduced to be controlled by the activation of hydrogen on Cu0 sites, which was further demonstrated by the correlations between the catalytic activity and different copper species. Importantly, this catalysis mechanism is different with that of gas‐phase diester hydrogenation, which is generally determined by the adsorption of ester on Cu+ species. [ABSTRACT FROM AUTHOR]

The geometry and relative stability of succinonitrile in the gas phase have been studied using DFT and ab initio calculations. The trans 1(A) and gauche 1(B) conformers found in succinonitrile are stemmed from the different positions of the two nitrile groups relative to each other. Our results suggest that the trans conformer is more stable than the gauche geometry by 0.65 and 1.01 kcal/mol using the CCSD/6‐311G+(d) and M06/ aug‐cc‐pVDZ calculations, respectively. The results from population analysis indicate that the gas phase is 64.4 % abundant of trans conformer. To imitate the crystal phase, unit cells containing four succinonitrile molecules have been optimized. The data suggest that the trans molar volume of the condensed phase 5(A, B) is smaller than the gauche form 4(A, B, C) by ∼50 Å3 per unit cell. Therefore, at extremely high pressures of up to about 2.9 GPa, the trans conformer predominates. On the contrary, the gauche conformer becomes the predominant isomer as the temperature of the system decreases. This is attributed to the higher stability exhibited by the gauche conformer unit cells compared to that of the trans conformer. [ABSTRACT FROM AUTHOR]

We consider the dynamics of exciton condensed phase pulses in two interacting quantum wells, in which excitons are excited and are acted upon by an external driving force. We use the phenomenological expression of free energy for excitons and take into account the finiteness of the exciton lifetime. It is assumed that the excitonic condensed phase arises due to the interaction between excitons, and that the condensed phase parameters depend on the exciton lifetime. In a long well, a periodic flow of pulses occurs, the speed of which depends on the driving force. It is shown that the distance between the pulses and other parameters can be controlled by irradiating another region of the quantum well, far from the observation region. [ABSTRACT FROM AUTHOR]

Theoretical calculations of physical and chemical conditions of the process of diffusion saturation of carbon steels with nitrogen, carbon and chromium in the conditions of low pressure in the chlorine environment are carried out. The probable phase composition as a result of diffusion saturation is determined. The temperature interval for the existence of carbides and nitrides was established. The main probable condensed and gas phases that are formed as a result of saturation of carbon steels with carbon, nitrogen and chromium are identified. It is analyzed how the number of condensed and gas phases changes depending on the temperature of the diffusion coating process. It is theoretically established that two chromium nitrides CrN and Cr2N and chromium carbide Cr3C2 will be the main condensed phases as a result of deposition of the protective coating. The temperature interval for the existence of the main strengthening phases is established. Systems with oxygen content are analyzed. The formation of chromium oxides in the gas state is noted. It is determined that in the first and final stages of saturation (the initial and final temperatures of the saturation process), the main chromium-containing phase is chromium carbide and the almost complete absence of Cr2N nitride. The temperature of 1300 K is the optimum temperature at which a complex chromium carbide-nitride coating is formed. This combination of protective coating layers will have optimum properties in terms of wear and corrosion protection. [ABSTRACT FROM AUTHOR]

Intriguing properties of photoemission from free, unsupported particles and droplets were predicted nearly 50 years ago, though experiments were a technical challenge. The last few decades have seen a surge of research in the field, due to advances in aerosol technology (generation, characterization, and transfer into vacuum), the development of photoelectron imaging spectrometers, and advances in vacuum ultraviolet and ultrafast light sources. Particles and droplets offer several advantages for photoemission studies. For example, photoemission spectra are dependent on the particle's size, shape, and composition, providing a wealth of information that allows for the retrieval of genuine electronic properties of condensed phase. In this review, with a focus on submicrometer-sized, dielectric particles and droplets, we explain the utility of photoemission from such systems, summarize several applications from the literature, and present some thoughts on future research directions. [ABSTRACT FROM AUTHOR]

Featured Application: Choosing appropriate DFT methodology for periodic modeling of porphyrin containing systems. Porphyrins are fascinating molecules with applications spanning various scientific fields. In this review we present the use of periodic density functional theory (PDFT) calculations to study the structure, electronic properties, and reactivity of porphyrins on ordered two dimensional surfaces and in the formation of nanostructures. The focus of the review is to describe the application of PDFT calculations for bridging the gaps in experimental studies on porphyrin nanostructures and self-assembly on 2D surfaces. A survey of different DFT functionals used to study the porphyrin-based system as well as their advantages and disadvantages in studying these systems is presented. [ABSTRACT FROM AUTHOR]

• Consumption mechanism of levoglucosan during cellulose pyrolysis was studied. • Dielectric constant of levoglucosan was calculated through DFT and MD simulation. • Condensation of pure levoglucosan is impossible during cellulose pyrolysis. • High temperatures above 800 K are needed for the obvious levoglucosan decomposition. • Levoglucosan decomposition is slightly promoted in the condensed phase. In this study, the condensation, as the fundamental step of polymerization, and decomposition mechanisms of levoglucosan in the condensed phase during cellulose pyrolysis were investigated using density functional theory (DFT) calculations to investigate non-specific solvent effects. The condensed phase was simulated using an implicit solvent model, while the dielectric constants of levoglucosan at different temperatures were determined by theoretical calculations. This study considered levoglucosan condensation reactions to form anhydro-disaccharides with various α and β linkages (including 1,2-, 1,3- and 1,4-glycosidic bonds) and levoglucosan decomposition reactions including 1,2-dehydration, 1,3-dehydration, and ring-opening reactions. Our results show that the formation of β-anhydro-disaccharides prefers the direct condensation mechanism of two levoglucosan molecules through a four-member ring transition state, while kinetically more disadvantageous α-anhydro-disaccharides are generally formed by the condensation of levoglucosan molecule and α-d-glucose from levoglucosan hydrolysis. However, levoglucosan condensation without catalysis is unlikely to take place at typical temperatures of cellulose pyrolysis, due to the low reaction rate at low temperatures. At high temperatures above 625 K, levoglucosan condensation is also inhibited due to the higher ΔGθ and lower reaction rates, compared to those of levoglucosan decomposition. A high temperature above 800 K is needed for the obvious decomposition of levoglucosan, mainly through the ring-opening reaction to form 5-keto-6-deoxy-glucose, which is further promoted by the dielectric environment of the condensed phase during cellulose pyrolysis. Further calculations on acetic acid-catalyzed levoglucosan condensation and decomposition suggest that the consumption of levoglucosan at low temperatures is mainly due to catalysis of acetic acid on polymerization and further decomposition of polymers. [ABSTRACT FROM AUTHOR]

Alkaloid chemistry is varied and complex. Many alkaloids attract a great deal of interest because of their physiological activity, yet surprisingly little is known about the thermochemistry of these compounds, especially in the gas phase. In this paper, we investigate the thermochemical characteristics, specifically demethoxylation enthalpies rather than those derived from trans-methoxylation reactions, of a series of biologically relevant alkaloids in their condensed phase.

Relevance of the work is related to the research of efficiency of using electric field for sedimentation of concrete substances to clean the room of aerosol pollution. Development of methods of ensuring purity of the environment and surface in closed working rooms, especially in the conditions of the developing production technologies, medicine and conditions of a person life support, are always actual and timely. The aim of the research is pilot and theoretical study of sedimentation at electric field interaction with particles of fine aerosols; based on the research to develop the effective ways of collecting various harmful substances from air and cleaning working room surface. Research methods: the optical diagnostics of an aerosol based on a method of low-angle dispersion with use of the laser measuring LID-2M complex and technology of laser diffraction (Malvern Spraytec analyzer); the tensometric method of weight measurement; the ejector dispersion method; the method of mechanical crushing of the dispersed powders. Results. The paper demonstrates the charge of aerosol particles at crown category. The authors have carried out the pilot studies of the model substances dispersion affected by the electric field and without it. The values of change in dispersion and mass concentration of the produced aerosol were obtained during the experiment by means of the laser LID-2M measuring machine. It was experimentally determined that the speed of aerosol particles sedimentation affected by the electric field increases several times, but not for all studied substances, large particles of aero force will quicker settle under gravitation. The authors calculated the characteristic speeds arising in the course of aerosol evolution for model substances. The paper introduces the comparative analysis of speeds of particle convective distribution in space, gravitational sedimentation and drift of aerosol cloud particles under electric forces. Based on the analysis it is possible to establish the effectiveness of using the electric field for sedimentation of concrete substance with certain dispersion. The data obtained should be considered as well when designing new installations of electric precipitators.

A mathematical model and the results of calculating the ignition and combustion of energetic condensed systems based on mono- and polydispersed aluminum diboride particles in air flows in constant-cross-section channels are reported. The kinetic characteristics of the transformations that separate aluminum diboride particles formed by gasification of energetic condensed systems undergo in a high-temperature oxidizing medium were determined using the dependences of the ignition induction period and combustion time on the air temperature and diameter and initial temperature of the particles. These dependences, in turn, were calculated using the model of parallel chemical reactions. The range of combustion conditions corresponding to the initial air temperatures from 300 to 2000 K and Mach numbers in the channel from 0.1 to 1.5 was considered. The influence of the aluminum diboride particle size and of the rate and initial temperature of the air flow on the combustion efficiency was demonstrated. The relationships between the combustion completeness factor of aluminum diboride particles at various initial parameters of the air flow and gasification products of energetic condensed systems at various fuel mixture equivalence ratios, corresponding to the diffusion and kinetic combustion, were determined. The conditions of the transition between the diffusion and kinetic control modes were found. [ABSTRACT FROM AUTHOR]

Abstract The oxidative and non-oxidative degradation behaviour of a flexible polyurethane foam, synthesised from toluene diisocyanate and a polyether polyol, is reported. Both toluene diisocyanate and diaminotoluene were identified as major products under non-oxidative conditions, which indicates that the urethane linkages are degrading by two competing degradation mechanisms. Degradation of the urethane linkage by a depolymerisation reaction to yield toluene diisocyanate and polyol is proposed to occur initially. In addition, the atmospheric pressure conditions favour the degradation of the urethane linkages via a six-membered ring transition state reaction to form diaminotoluene, carbon dioxide and alkene terminated polyol chains. Solid-state 13C NMR spectroscopy and elemental analysis of the residues indicates that at temperatures above 300 °C ring fusion of the aromatic components within the foam occurs, and this leads to a nitrogen-containing carbonaceous char which has a complex aromatic structure. It is proposed that under the confined conditions of the degradation the aromatic nitrogen-containing species, such as toluene diisocyanate and diaminotoluene, undergo secondary reactions and ring fusion to yield a complex char structure. Under oxidative conditions, degradation, including ring fusion, occurs at a lower temperature than under non-oxidative conditions. Neither toluene diisocyanate nor diaminotoluene were observed as major degradation products. The polyol is observed to undergo thermo-oxidative degradation at much lower temperatures than purely thermal degradation. As a consequence, the depolymerisation reaction via the six-membered ring transition state is limited in extent and diaminotoluene is not evolved. The absence of toluene diisocyanate is proposed to be a result of this species undergoing oxidative degradation reactions which lead to it being incorporated into the char. Highlights • Under non-oxidative conditions urethane linkages degrade by two competing mechanisms. • Above 300 °C under inert conditions ring fusion of the aromatic components occurs to yield a complex nitrogen-containing char structure. • Ring fusion is accelerated under oxidative conditions. [ABSTRACT FROM AUTHOR]

In this microreview we revisit the early work in the development of Transition State Theory, paying particular attention to the idea of a dividing surface between reactants and products. The correct location of this surface is defined by the requirement that trajectories not recross it. When that condition is satisfied, the true transition state for the reaction has been found. It is commonly assumed for solution‐phase reactions that if the potential energy terms describing solvent‐solute interactions are small, the true transition state will occur at a geometry close to that for the solute in vacuo. However, we emphasize that when motion of solvent molecules occurs on a time scale similar or longer than that for structural changes in the reacting solute the true transition state may be at an entirely different geometry, and that there is an important inertial component to this phenomenon, which cannot be described on any potential energy surface. We review theories, particularly Grote‐Hynes theory, which have corrected the Transition State Theory rate constant for effects of this kind by computing a reduced transmission coefficient. However, we argue that searching for a true dividing surface with near unit transmission coefficient may sometimes be necessary, especially for the common situation in which the rate‐determining formation of a reactive intermediate is followed by the branching of that intermediate to several products. The motion of solvent molecules for solution phase reactions is not always fast with respect to the changes in the reacting solute. Slow solvent motion will cause a relocation of the transition state, even if the underling potential energy surface is unaffected. The effect is visualized with a new model. Finding the location of the true transition state can be very important for calculating product ratios. [ABSTRACT FROM AUTHOR]

Porphyrins are fascinating molecules with applications spanning various scientific fields. In this review we present the use of periodic density functional theory (PDFT) calculations to study the structure, electronic properties, and reactivity of porphyrins on ordered two dimensional surfaces and in the formation of nanostructures. The focus of the review is to describe the application of PDFT calculations for bridging the gaps in experimental studies on porphyrin nanostructures and self-assembly on 2D surfaces. A survey of different DFT functionals used to study the porphyrin-based system as well as their advantages and disadvantages in studying these systems is presented.

Flotation of ions and molecules represents a promising method of separating components from solution, or in our case, gelled copper salt from blue water. The method of flotation of ions and molecules is basically the flotation extraction process which produces different concentration gradients of multicomponent condensed phase system. Different concentration gradients in the flotation extraction are due to the driving forces of participating molecules driven by molecular interactions. Multicomponent condensed phase system, i.e. flotation pulp, consists of water molecules of solute, and a suitable reagent which has the role of connection the liquid and gaseous phases dispersed in a biphasic system. Such a system leads to the interaction of solute with reagent to the formation of coagulated component in water as solvent. Separation in the polyphased system is in accordance with the Van't Hoff equation, and spontaneously occurs in two-phase systems like gaseous-fluid, such as the system of flotation pulp. Using the osmotic pressure in a column flotation machine comes to separation of flotation pulp into heavy and light phase. This allows the water molecules to form their natural distances which are only valid for molecules of pure water or heavy phase. Also, the solute forms its light phase, copper - surfactant salt as insoluble product. For some polyphase systems such as colloidal systems like in the flotation process are sufficient atmospheric pressure conditions, and for others solutions should be applied overpressure while being aerated. This paper presents the results of research the flotation extraction of blue water, i.e. copper solution content of 0.2 g/l. It is concluded from results that there is a possibility of purifying the blue water from the copper mine tailing dump using the flotation extraction technology.

Abstract We theoretically investigate internal conversion processes of a photoexcited molecule in a condensed phase. The molecular system is described by two-dimensional adiabatic ground and excited potential energy surfaces that are coupled to heat baths. We quantify the role of conical intersection (CI) and avoided crossing (AC) in the PESs in dissipative environments by simulating the time evolution of wavepackets to compute the lifetime of the excited wavepacket, yield of the product, and adiabatic electronic coherence. For this purpose, we employ the multi-state quantum Fokker-Planck equation (MSQFPE) for a two-dimensional Wigner space utilizing the Wigner–Moyal expansion for the potential term and the Brinkman hierarchy expression for the momentum. We find that the calculated results are significantly different between the CI and AC cases due to the transition in the tuning mode and vibrational motion in the coupling mode. [ABSTRACT FROM AUTHOR]

In this work, we explore the effect of solvent on 13 C and 81 Br kinetic isotope effects (KIEs) during elimination of bromine substituent from brominated organic compounds promoted by hydroxyl anion. In the present study, we investigate HBr elimination from 2-bromoethylbenzene in three different polar media (water, ethanol, and acetonitrile) as well as bromide ion elimination from 1,2-dibromoethane upon nucleophilic substitution by the hydroxyl ion in aqueous solution using carbon and bromine isotope analysis as mechanistic tools. We reconsider the hypothesis that the magnitude of leaving group halide KIE should visibly depend on the solvent and bond-breaking in a protic solvent should be accompanied by hydrogen bonding which would result in less zero-point energy loss than in an aprotic solvent. Modeling the elimination reaction using the available popular theoretical methods along with different approaches for including environment effects we demonstrate in the presented study no interpretable effect of the solvent on the transition state structure and hence on the theoretically predicted KIEs. The comparison of the magnitudes of carbon and bromine kinetic isotope effects for two different mechanistic pathways (elimination vs substitution) is also discussed. [ABSTRACT FROM AUTHOR]