Saccharin: a combined experimental and computational thermochemical investigation of a sweetener and sulfonamide

The standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous phase at a temperature of 298.15?K have been experimentally determined for saccharin and for benzenesulfonamide. These compounds were also studied theoretically using density functional theory, the B3LYP functional and extended basis sets.     

Kinetics and mechanism for the oxidation of anilines by ClO2: a combined experimental and computational study

The oxidation of para‐substituted anilines (X–C₆H₄NH₂, X = –CH₃, –H, –Cl, –NO₂) with chlorine dioxide was studied as a means of eliminating these pollutants. The oxidation rate decreases from that for 4‐methylaniline to that for 4‐nitroanilinem in agreement with the Hammett plot; the oxidation kinetics is second order in aniline and first order in ClO₂, for which a possible mechanism is proposed. Liquid chromatography and gas chromatography mass spectrometry results show that benzoquinone is formed as the major intermediate in aniline/ClO₂ oxidation, and the reaction is pH‐dependent as the rate constant increases with increasing pH. To further support our proposed mechanism, Density Functional Theory (DFT) computations at both B3LYP/6‐311 + G(d,p) level with the polarizable continuum model with an integral equation formalism solvation model (i.e., with water) were carried out, showing that activation energy barriers predict the same reactivity trend as shown by the kinetics experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

High pressure X-ray diffraction study of CaMnO3 perovskite

Using a diamond anvil cell device and synchrotron radiation,the in-situ high-pressure structure of CaMnO3 has been investigated.In the pressure up to 36.5 GPa,no pressure-induced phase transition is observed.The pressure dependence on the lattice parameters of CaMnO3 is reported,and the relationship of the axial compression coefficients is βa >βc > βb.The isothermal bulk modulus K298=224(25)GPa is also obtained by fitting the pressure-volume data using the Murnaghan equation of state.     

High pressure X-ray diffraction study of CaMnO3 perovskite

Using a diamond anvil cell device and synchrotron radiation,the in-situ high-pressure structure of CaMnO3 has been investigated.In the pressure up to 36.5 GPa,no pressure-induced phase transition is observed.The pressure dependence on the lattice parameters of CaMnO3 is reported,and the relationship of the axial compression coefficients is βa 〉 βc 〉 βb.The isothermal bulk modulus K298=224（25） GPa is also obtained by fitting the pressure-volume data using the Murnaghan equation of state.     

Equation of state of asymmetric nuclear matter: a VMC study

A Variational Monte Carlo (VMC) method is employed to investigate the properties of symmetric and asymmetric nuclear matter. The realistic Urbana V ₁₄ twonucleon interaction potential of Lagaris and Pandharipande was used to describe the microscopic interactions. Also, many body interactions are included as a density dependent term in the potential. Total kinetic and potential energies per particle are calculated for asymmetric nuclear matter by VMC method at various densities and isospin asymmetry parameters. The results are compared with data found in literature, and it was observed that the results obtained in this study reasonably agree with the results found in the literature. Also, the symmetry energy and incompressibility factor of the nuclear matter were obtained. The results obtained are in good agreement with those obtained by various authors with different methods and techniques.     

Raman study of a photochromic diarylethene molecule: a combined theoretical and experimental study

In this paper, the photochromic reaction of the 1,2‐bis(5′‐ethoxy‐2′‐(2″‐pyridyl) thiazolyl) compound (named DE) was studied by ultraviolet–visible absorption and various Raman spectroscopies associated with density functional theory calculations. To explain the growth of the visible absorption spectrum when the compound is irradiated with ultraviolet light, we suggest the existence of several conformations of the colored form. We also studied the vibrational spectroscopic properties of DE in different conditions such as powder, thin solid film, or in gold nanorods colloidal solutions. This compound is found photochromic in all these conditions. The theoretical Raman spectra of the open and closed forms reproduce fairly well the experimental data and help the complete assignment of the observed bands. Copyright © 2013 John Wiley & Sons, Ltd.     

Equation of state of solid 3He

We present results of diffusion Monte Carlo calculations for the bcc and hcp phases of solid 3He, using a recent ab initio interatomic potential, including two- and three-body terms. This potential is found to yield an equation of state for condensed 4He in excellent agreement with experiment, in a wide density range. For 3He, we find a systematic discrepancy, worth 0.7 K, between our computed equation of state and a commonly accepted experimental one. We attribute such a discrepancy to an improper choice of reference energy in the determination of the experimental equation of state.     

On the mechanism of xylan pyrolysis by combined experimental and computational approaches

Pyrolysis is the initial stage of biomass combustion, whereas, the pyrolysis mechanism of biomass, especially the hemicellulose component, is still not well elucidated. Herein, a common hemicellulose polysaccharide, xylan, was investigated to reveal the evolution of volatiles and solid residue through combined thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFT) techniques. Quantum chemistry calculation was also conducted to analyze the primary xylan pyrolysis mechanism by using a long-chain xylan model which was built based on the structural characterization of xylan. The experimental results indicated that the functional groups in solid-phase evolved intensively during the main weight loss zone (200–350 °C), leading to the violent release of volatiles. The decomposition of branches, especially the arabinose unit, was prior to that of the backbone, with relatively low energy barriers and high rate constants. The initial enhancement of CO vibration in solid-phase above 200 °C derived from the formation of the furanose unit. Both dehydration and breakage of glycosidic bonds were responsible for the formation of CC bond in solid-phase from 300 °C. The cracking of the 4-O-Me group resulted in the release of aldehydes to gas-phase in the main weight loss zone (200–350 °C). The scission of the whole 4-O-MeGlc unit and/or the rupture of the uronic acid group led to the gas-phase CO bond formation.     

Valence structures of aromatic bioactive compounds: a combined theoretical and experimental study

Valence electronic structures of three recently isolated aryl bioactive compounds, namely 2‐phenylethanol (2PE), p‐hydroxyphenylethanol (HPE) and 4‐hydroxybenzaldehyde (HBA), are studied using a combined theoretical and experimental method. Density functional theory‐based calculations indicate that the side chains cause electron charge redistribution and therefore influence the aromaticity of the benzene derivatives. The simulated IR spectra further reveal features induced by the side chains. Solvent effects on the IR spectra are simulated using the polarizable continuum model, which exhibits enhancement of the O—H stretch vibrations with significant red‐shift of 464 cm^?1 in 2PE. A significant spectral peak splitting of 94 cm^?1 between O(4)—H and O(8)—H of HPE is revealed in an aqueous environment. Experimental measurements for valence binding energy spectra for 2PE, HPE and HBA are presented and analyzed using outer‐valence Green function calculations. The experimental (predicted) first ionization energies are measured as 9.19 (8.79), 8.47 (8.27) and 8.97 (8.82) eV for 2PE, HPE and HBA, respectively. The frontier orbitals (highest occupied molecular orbitals, HOMOs, and lowest unoccupied molecular orbitals, LUMOs) have similar atomic orbital characters although the HOMO–LUMO energy gaps are quite different.     

A computational and experimental study of resonators in three dimensions

In a previous work by the present authors, a computational and experimental investigation of the acoustic properties of two-dimensional slit resonators was carried out. The present paper reports the results of a study extending the previous work to three dimensions. This investigation has two basic objectives. The first is to validate the computed results from direct numerical simulations of the flow and acoustic fields of slit resonators in three dimensions by comparing with experimental measurements in a normal incidence impedance tube. The second objective is to study the flow physics of resonant liners responsible for sound wave dissipation. Extensive comparisons are provided between computed and measured acoustic liner properties with both discrete frequency and broadband sound sources. Good agreements are found over a wide range of frequencies and sound pressure levels. Direct numerical simulation confirms the previous finding in two dimensions that vortex shedding is the dominant dissipation mechanism at high sound pressure intensity. However, it is observed that the behavior of the shed vortices in three dimensions is quite different from those of two dimensions. In three dimensions, the shed vortices tend to evolve into ring (circular in plan form) vortices, even though the slit resonator opening from which the vortices are shed has an aspect ratio of 2.5. Under the excitation of discrete frequency sound, the shed vortices align themselves into two regularly spaced vortex trains moving away from the resonator opening in opposite directions. This is different from the chaotic shedding of vortices found in two-dimensional simulations. The effect of slit aspect ratio at a fixed porosity is briefly studied. For the range of liners considered in this investigation, it is found that the absorption coefficient of a liner increases when the open area of the single slit is subdivided into multiple, smaller slits.     

Tautomery and H-bonding characteristics of 2-aminopurine: a combined experimental and theoretical study

An experimental and theoretical RHF, MP2 and DFT/6-31++G^** study is described of the matrix FT-IR spectra of monomer 2-aminopurine and H-bonded complexes of 2-aminopurine with water. 2-aminopurine occurs in Ar predominantly as the amino-N9H tautomer, but small amounts of the amino-N7H tautomer are also present. An approximate K_T value for this tautomeric equilibrium is found to be 0.016 (RHF) and 0.015 (DFT) using the infrared intensity measurement. Four H-bonded complexes of the abundant amino-N9H form with water are detected in the experimental FT-IR spectrum by their characteristic predicted absorptions, i.e. the three closed complexes N3 ^... H-O ^... H-N9, N1 ^... H-O ^... H-NH, N3 ^... H-O ^... H-NH and the open complex N7 ^... H-OH. From the experimental results, the proton affinity of the N7 atom in 2-aminopurine can be estimated. The dependence of the H-bond strength on the H-bond linearity is demonstrated by a correlation between the N ^... H distance and the N ^... H-O angle in closed N ^... H-O ^... H-N complexes. Received 10 December 2001 Published online 13 September 2002     

Equation of state of a Fermi gas in the BEC-BCS crossover: a quantum Monte Carlo study

We calculate the equation of state of a two-component Fermi gas with attractive short-range interspecies interactions using the fixed-node diffusion Monte Carlo method. The interaction strength is varied over a wide range by tuning the value a of the s-wave scattering length of the two-body potential. For a>0 and a smaller than the inverse Fermi wave vector our results show a molecular regime with repulsive interactions well described by the dimer-dimer scattering length a(m)=0.6a. The pair correlation functions of parallel and opposite spins are also discussed as a function of the interaction strength.     

New insights into corona discharge surface ionization of polyethylene terephthalate via a combined computational and experimental assessment

The aim of the present work is to demonstrate the influence of corona discharge ionization on chemical and physical properties of polyethylene terephthalate (PET) fibers using computational and experimental studies. In the computational section, the vibrational frequencies of proposed models for PET before and after corona discharge treatment were predicted in the liquid phase at both the B3LYP/6-31G/COSMO and B3PW91/6-31G/COSMO level of theories using the harmonic approximation. When compared to B3LYP, the frequencies obtained for the B3PW91 show a better linear correlation with the experimental data. Furthermore, experimental studies were carried out by the use of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and reflectance spectroscopy (RS). Experimental evidence indicated that the corona discharge modifies the surface of fibers and also increases the reactivity of PET toward cationic dyes. Our combined computational and experimental parametric study clearly confirms that the changes occurred on the PET surface due to corona discharge ionization.     

Ylide stabilized carbenes: a computational study

High‐level Density Functional Theory calculations, coupled with appropriate isodesmic reaction, are employed to investigate the effects of α‐carbon, ammonium, phosphorus, and sulfur ylides, cyclization, and unsaturation on the stability, multiplicity, and reactivity of novel singlet (S) and triplet (T) carbenes. Among them the highly π‐donating α‐ammonium ylide is found to exert the highest stabilizing effect on the carbenic center. α‐Ammonium ylides resist dimerization and hydrogenation. They show wider singlet–triplet energy gap (ΔΕ_S–T), broader band gap (ΔΕ_HOMO–LUMO), and higher nucleophilicity compared to the reported stable N‐heterocyclic carbenes. Aromatic cyclic unsaturated ammonium, phosphorus, and sulfur ylide carbenes appear more stable than their saturated cyclic analogs which are in turn more viable than their acyclic counterparts. Copyright © 2014 John Wiley & Sons, Ltd.     

Equation of state of a real gas

It is shown using 28 gases as an example that the Van der Waals equation in the form $$\left[ {P + \frac{a}{{(V + c)^k T^m }}} \right](V - b) = RT$$ correctly expresses quantitative relations between parameters P, V, and T for real gases. Here, a, b, and c are constants; k is a number close to 2; and m varies in the range 0.2–2.17 for different gases. The critical parameters of most gases calculated by this formula are found to be close in value to the experimental parameters.     

Joint experimental and computational study of aluminum electron energy loss spectra

Experimental reflection electron energy loss (REEL) spectra are measured from aluminum for primary energies ranging from 130 eV to 2 keV. A Monte Carlo simulation is shortly described and used to calculate the same spectra. The focus is on reproducing the variable weight of surface and bulk losses as the surface sensitivity of spectra changes by changing the primary electron energy. The intensity of surface losses in the simulations is modulated by the thickness of the region where surface excitations occur. Simulations based either on a constant or an energy-dependent thickness for this layer are considered. In both cases, simulated spectra reproduce the experimental trend as a function of energy, though the correct surface-to-bulk intensity ratio for each energy is either underestimated or overestimated.     

Computer simulation of the oxygen mobility in CaMnO3-x

The perovskite-type metal oxide CaMnO_3-x is known to accommodate substantial amounts of oxygen vacancies. High-resolution electron microscope investigations give evidence for ordering of the vacancies, i.e. well-defined structures in the compositional range of CaMnO_2.5 < CaMnO_3-x < CaMnO₃. Within this range the metal cation positions do not change, i.e. perovskitic framework is conserved while a remarkably high oxygen anion mobility is recorded. In addition, the electronic and magnetic structure, and thus the physical properties, depend directly on the oxygen stoichiometry.

This contribution focusses on the oxygen mobility in different CaMnO_3-x phases exhibiting oxygen vacancy ordered structures, i.e. CaMnO_3.0, CaMnO_2.80, CaMnO_2.75, CaMnO_2.66, CaMnO_2.55 and CaMnO_2.50. In these compounds the formal oxidation state of manganese changes from Mn⁴⁺ (x=0) to Mn³⁺ (x=0.5).

For the computer simulation of the defect structure and for the mobility of the oxygen anions within these defect structures we applied the method of interatomic potentials in a simple rigid-ion approximation. The parameters of interaction were calibrated on the basis of empirical data. i.e. equilibrium geometry and cohesive energies of the binary oxides CaO, MnO₂ and Mn₂O₃ were taken into account for the present calculations.

Stabilities, oxygen migration barriers and dielectric constants of selected representants of CaMnO_3-x are presented.     

Equation of state for a hard-sphere mixture

The equation of state for a multicomponent hard-sphere system is derived using the method of accelerated convergence of the perturbation series. In the asymptotic limit of small densities, this equation reproduces the virial coefficients known for the systems in question. In the case of a one-component system, the equation transforms into a form that adequately describes both the stable and metastable phases of the substance.     

Electron leakage and double-exchange ferromagnetism at the interface between a metal and an antiferromagnetic insulator: CaRuO3/CaMnO3

Density-functional electronic structure studies of a prototype interface between a paramagnetic metal and an antiferromagnetic (AFM) insulator (CaRuO(3)/CaMnO(3)) reveal the exponential leakage of the metallic electrons into the insulator side. The leaked electrons in turn control the magnetism at the interface via the ferromagnetic (FM) Anderson-Hasegawa double exchange, which competes with the AFM superexchange of the bulk CaMnO3. The competition produces a FM interfacial CaMnO3 layer (possibly canted); but beyond this layer, the electron penetration is insufficient to alter the bulk magnetism.