The second virial coefficients of the hydrogen isotopes between 20 and 70°K

The second virial coefficients of H₂, HD and D₂ are measured at low densities in the temperature region between 20 and 70°K using differential method. The measurements confirmed the results of the isotherm determinations of Beenakker e.a.¹). At the higher temperatures good agreement with the existing data was found.     

The second virial coefficient of binary mixtures of the hydrogen isotopes and helium AT 20.4°K

The excess second virial coefficient, E, of binary mixtures of the hydrogen isotopes and helium has been measured. The E for a mixture of a hydrogen isotope with He is quite large. There is reasonable agreement with the excess values derived from absolute measurements. For mixtures of the hydrogen isotopes, in agreement with theoretical predictions, no excess could be detected.     

Rate coefficients for the gas-phase reaction of OH radical with α-pinene: an experimental and computational study

The rate coefficient for the gas-phase reaction of OH radical with α-pinene was measured at 298 K using relative rate methods, with propylene as a reference compound. The ratio of the rate coefficient for the reaction of OH radicals with α-pinene to that of with OH radicals with propylene was measured to be 1.77 ± 0.21. Considering the absolute value of the rate coefficient of the reaction of OH radicals with propylene as (3.01 ± 0.42)×10^?11 cm³ molecule^?1 s^?1, the rate coefficient for the reaction of OH radicals with α-pinene was determined to be (5.33 ± 0.79)×10^?11 cm³ molecule^?1 s^?1. To gain a deeper insight into the reaction mechanism, theoretical calculations were also carried out on this reaction. The rate coefficient of OH radical with α-pinene was calculated using canonical variational transition state theory with small-curvature tunnelling. The kinetics data obtained over the temperature range of 200–400 K were used to derive the Arrhenius expression: k(T) = 3.8×10^?28 T^5.2 exp[2897/T] cm³ molecule^?1 s^?1. The OH-driven atmospheric lifetime (τ) and ozone formation potential of α-pinene were calculated and reported in this work.     

Atomic additivity of the correlation energy in molecules—an ab initio MP4 and G3 study

It is shown that the closed shell valence electron molecular correlation energy of organic molecules in their ground states is a homogeneous multilinear function of the numbers of neutral atoms in their canonical hybridization state. The additivity is a robust feature, which holds for MP2(fc), MP3(fc) and MP4(fc) model calculations. The latter results obtained on a test set of 91 widely different organic molecules, exhibiting a whole gamut of electronic structure patterns, are excellent as evidenced by the absolute average deviation from the additivity values (AAD) of only 1.4 kcal mol^?1 and R ² = 0.999 93. The maximum absolute deviation (MAD) is 5.3 kcal mol^?1. The additivity formula for the total molecular electron correlation retrieved from G3 calculations also has an excellent performance (AAD = 1.2 kcal mol^?1, R ² = 0.999 98 and MAD = 7.2 kcal mol^?1). If it is taken into account that the additivity formulae require only back of the envelope calculations, these results are remarkable indeed, in particular since the G3 correlation energies span a very large range from 180.7 (methane) to 1642.8 (hexafluorocyclopropane) kcal mol^?1. Comparison of the exact electron correlation energies in free atoms with the corresponding average correlation energies in molecules reveals that a substantial increase in the latter provides an important contribution in overcoming a very strong Coulomb repulsion between the nuclei. It is shown that the additivity formulae are useful in detecting some special molecular features such as strong resonance and anti-aromaticity.     

The effect of hydrogen-bonding cooperativity on the strength and properties of σ-hole interactions: an ab initio study

Ab initio calculations at the MP2/aug-cc-pVTZ level of theory are performed to investigate the effect of hydrogen-bonding cooperativity on the strength and bonding properties of σ-hole interaction in linear FCl???(NCH)_n=2–5, FHS???(NCH)_n=2–5, FH₂P???(NCH)_n=2–5 and FH₃Si???(NCH)_n=2–5 clusters. It is found that the cooperative effects in the hydrogen-bonding tend to strengthen the σ-hole interaction. However, these effects are almost saturated in the larger clusters (n > 5). For a given cluster, the amount of bond contraction in FCl???(NCH)_n is more important than other systems. A nice linear relationship is found between the σ-hole bond energies and absolute ¹⁵N chemical shieldings or spin–spin coupling constants across the σ-hole bond.     

Effect of low level laser irradiation on the proliferation of myoblasts—the skeletal muscle precursor cells: an experimental in vitro study

The aim of this paper is to study the effect of low-level laser irradiation (LLLI) on proliferation of myoblasts in culture. Myoblasts derived from rat skeletal muscle were irradiated by He-Ne laser with different doses. Compared with nonirradiated control group, the number of myoblasts increased when the cells in normal culture conditions were exposed to the laser of specific energy density. The amount of cells with proliferating cell nuclear antigen (PCNA) positive expression and the 5-bromo-2′-deoxyuridine (BrdU) incorporation rate after laser irradiation were also higher than that of the control group, suggesting that LLLL at certain doses can effectively enhance myoblasts growth activity in vitro. This study firstly demonstrated that stimulating myoblasts to enter into proliferative stage from initial resting state was an important mechanism of regeneration and repair of injured skeletal muscle promoted by LLLI in clinical treatment.     

Modeling the non-Arrhenius ignition behavior of 2‐butanol: A detailed theoretical and experimental study

2-butanol is a promising alternative to fossil fuels for which production pathways are already established and which was proven to be suitable for usage within modern internal combustion engines. It is a potential octane booster for gasoline fuels, can be used in diesel engines to reduce soot production, and is applicable as a stand-alone fuel. In the present study, the previously not discussed non-Arrhenius ignition behavior of 2-butanol was revealed by recalculating and adjusting the thermodynamic properties of the fuel and its most important radicals. All relevant fuel consumption reaction rate coefficients were replaced by a consistent set of analogies without any further modifications of the rate parameters. The existing spectrum of validation targets for 2-butanol was extended by new high-pressure Rapid Compression Machine (RCM) experiments for end-of-compression pressures of  =  20, 30, 40, and 50 bar with high resolution of temperature to highlight the non-Arrhenius ignition behavior and to study the model performance in more detail. The kinetic model proposed in the present study can reproduce the observed non-Arrhenius behavior within the RCM regime. Kinetic analysis demonstrated that simulated Ignition Delay Times (IDTs) are very sensitive to the equilibria of the  +  reactions for all 2-hydroxybutyl radicals. With the newly determined thermodynamic properties, the equilibria of the  +  reactions are moved towards lower temperatures, enabling low-temperature chain branching. The shift of the equilibrium from the R side to  +  within the temperature regime covered by the RCM experiments could be identified as the main reason for the observed non-Arrhenius behavior.     

Experimental and ab initio study of the nuclear quadrupole interaction of 181 Ta-probes in an α-Fe2O3 single crystal

We report perturbed-angular-correlation (PAC) experiments on ¹⁸¹Hf (→¹⁸¹Ta)-implanted corundum α-Fe₂O₃ single crystal in order to determine the magnitude, symmetry and orientation of the electric-field-gradient (EFG) tensor at Ta donor impurity sites of this semiconductor. These results are analyzed in the framework of ab initio full-potential augmented-plane wave plus local orbital (FP-APW+lo) calculations. This combined analysis enables us to quantify the magnitude of the lattice relaxations induced by the presence of the impurity and to determine the charge state of the impurity donor level introduced by Ta in the band gap of the semiconductor.     

Magnetization dynamics of mixed Co–Au chains on Cu(110) substrate:Combined ab initio and kinetic Monte Carlo study

We present an investigation of the one-dimensional ferromagnetism in Au–Co nanowires deposited on the Cu(110)surface. By using the density functional theory, the influence of the nonmagnetic copper substrate Cu(110) on the magnetic properties of the bimetallic Au–Co nanowires is studied. The results show the emergence of magnetic anisotropy in the supported Au–Co nanowires. The magnetic anisotropy energy has the same order of magnitude as the exchange interaction energy between Co atoms in the wire. Our electronic structure calculation reveals the emergence of new hybridized bands between Au and Co atoms and surface Cu atoms. The Curie temperature of the Au–Co wires is calculated by means of kinetic Monte Carlo simulation. The strong size effect of the Curie temperature is demonstrated.     

Superhalogen properties of ReOn (n = 1–5) species and their interactions with an alkali metal: an ab initio study

First principle density functional approach is employed to investigate the ground-state geometries and stabilities of ReO_n species (n = 1–5) in neutral as well as anionic forms. It is revealed that Re can bind stably with five O atoms indicating the maximum oxidation state of Re as high as +10. The electron affinities of ReO_n suggest that these species behave as superhalogens for n ≥ 3 which become as large as 7.25 eV for n = 5. The interaction of ReO_n superhalogens with appropriate alkali metals is stronger than that of halogens leading to the synthesis of more stable complex compounds. This idea is illustrated by considering the interaction of ReO_n superhalogens with K atom, forming KReO_n complexes which are relatively more stable than KF molecule. In such complexes, ReO_n unit closely mimics the behaviour of F atom when compared with KF.     

Structural,optical and gas sensing properties of Cu2O/CuO mixed phase: effect of the number of coated layers and (Cr + S) co-Doping

Thin films of Cu₂O/CuO mixed phase have been deposited on pre-cleaned glass substrate by a spin-coating technique. The influence of Cr-doping, (Cr?+?S) co-doping and the number of coated layers on the structures and optical behaviors of the films were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman, and UV-Visible spectroscopies. From XRD, FTIR and Raman results; the films are composed of polycrystalline monoclinic CuO and cubic Cu₂O phases with crystallite sizes ranged from 10.05 to 23.08?nm. Increasing the thickness improves the films’ crystallinity and decreases the defects level in the films. Cr and S incorporation encourages the growth of CuO phase at the expense of Cu₂O one and affects the preferred growth direction. The doping with Cr and S blue shifted the B_g mode and multi-phonon transitions. The direct and indirect optical band gaps decreased from 2.25?eV and 1.60?eV to 2.10?eV and 1.20?eV by growing the number of deposited layers from 2 to 8 layers. The film sensitivity towards CO₂ at different gas flow rate was studied and compared with those of similar systems. Also; response time, recovery time, detection limit, and limit of quantification are estimated.     

Car—Parrinello study of Ziegler—Natta heterogeneous catalysis: stability and destabilization problems of the active site models

Recent results on Car—Parrinello simulations of MgCl₂/TiCl₄ Ziegler—Natta heterogeneous catalytic systems are reviewed and the stability of Ti active site configurations on the various active surfaces are discussed. In particular, the focus is on the ability of an active centre to carry out the polymerization process efficiently, achieved by monitoring geometrical changes and associated energetics during the reaction. The active site geometry is crucial in enhancing or decreasing the activation barrier, in selecting the olefin enantioface and in some cases in destabilizing the catalytic centre. A key point in the binding/destabilization interplay is the matching of Ti with the substrate, an issue that represents a fundamental difference with respect to homogeneous systems.     

The phosphorescent triplet state of p-xylene in an isotopically mixed crystal at 1·2K: an investigation by E.S.R. and MIDP

The phosphorescence spectrum of p-xylene-h ₁₀ in a p-xylene-d ₁₀ host is first presented. Secondly we report E.S.R. experiments performed on p-xylene-α,α′-d ₆ in p-xylene-d ₁₀; from an analysis of the orientations of the principal axes in combination with the crystal structure and of the hyperfine splittings it is concluded that the in-plane principal axes of the zfs tensor make an angle of 68° with the molecular axes. Thirdly we discuss Microwave-Induced Delayed Phosphorescence (MIDP) experiments on p-xylene-h ₁₀ in p-xylene-d ₁₀ in which the relative radiative rate constants for decay from the zero-field spin components of the triplet state to single vibronic bands of the ground state have been obtained.

The results of the MIDP and E.S.R. measurements are shown to be mutually consistent in terms of a model in which the effect of the crystal field and the methyl substituents on the pseudo-Jahn-Teller unstable electronic structure of the triplet state of benzene is described.     

A model for the spatial distribution and transport properties of defects in mixed ionic-electronic conductors part I: Defect concentration — Pressure relationships and the spatial distribution of defects

The spatial distribution and transport of defect species in a mixed ionic-electronic conductor (MIEC) depend on the activity of the external gas phase at either side of the MIEC, the defect equilibria and mobility of the species within the MIEC. Previous researchers [1, 2] developed models for defect distribution and transport based on various assumptions, the most prevalent of which is that the concentration of the ionic defect species is constant through the range of activities of the external gas phase in which the MIEC finds application. However, the defect equilibria for many MIECs do not support this assumption. It is desirable, therefore, to have explicit, analytical expressions for the spatial distribution of the defects as a function of position and the flux as a function of the activity gradient of the defect species and the gas phase. Towards the development of such a model, the defect concentration-oxygen partial pressure dependence in an oxide MIEC, such as Ce_0.8Sm_0.2O_2−δ, is considered. From the defect equilibria, equations are developed for the dependence of the defect species on the oxygen activity in the oxide MIEC. Then, to relate the defect equilibria to the spatial parameters of the MIEC, an analytic expression for the variation of oxygen activity as a function of position in an electrolyte is derived. Equations relating oxygen activity to position and defect concentration to oxygen activity are then combined to obtain a defect concentration-position relation. All the relations are derived without the assumption of constant vacancy concentration. Finally, the results are compared with those of previous models.     

Is the established structure of α-rhombohedral boron correct? Comparative study of IR-active phonons with B6O, B4.3C and β-rhombohedral boron

The established structure of α-rhombohedral boron, based on one B(12) icosahedron per unit cell only, is put in question. A careful evaluation of the IR-active phonons in comparison with B(6)O, B(4.3)C and β-rhombohedral boron makes it evident that-aside from the B(12) icosahedra-the α-rhombohedral boron structure also contains single boron atoms. We assume these single atoms replace the currently assumed inter-icosahedral three-centre-bonds by covalently saturating the outward directing bonds of the equatorial atoms of the three adjacent icosahedra. Indeed, the implied structure formula B(12)B(2) is not supported by previous density measurements. The IR-phonon spectra of the related structures are correlated and merely shifted relative to one another; significant features depend quantitatively on the actual structure, but they can be easily allocated.     

Theoretical study of the LiNa molecule beyond the Born–Oppenheimer approximation: adiabatic and diabatic potential energy curves,radial coupling,adiabatic correction,dipole moments and vibrational levels

ABSTRACT

The adiabatic potential energy curves for ground and many excited states of ^{1, 3}Σ⁺, ^1,3Π, ^1,3Δ symmetries of the LiNa molecule have been performed. We have used an ab initio approach based on non-empirical pseudopotentials, parameterised l-dependent polarisation potentials and full configuration interaction calculations. In addition, the adiabatic potential energy curves determined in our previous work [Mabrouk and Berriche, J. Phys. B: At. Mol. Opt. Phys. 41, 155101 (2008).] are corrected by using a diabatisation procedure, based on the effective Hamiltonian theory and an effective metric. The diabatic permanent moments for first 10 ¹Σ⁺ electronic states show linear behaviours, especially at intermediate and large distance. The transition dipole moment between neighbour states has revealed many peaks located around the avoided crossing positions. The radial coupling between the adiabatic states was calculated using the Hellmann-Feynman formula and numerical differentiation of the rotation matrix. The first and the second derivatives revealed many peaks, associated to neutral-neutral and ionic-neutral crossings. Furthermore, the radial coupling is used to evaluate the adiabatic correction, which is found to be of an order of tens and hundreds of cm^?1, especially of higher excited states. In addition, we have determined the vibrational level spacing for all studied states.     

High resolution FTIR study of the ν5 and ν6 bands of CH2D35Cl: analysis of resonances and determination of ground and upper state constants

The isotopically pure form of methyl chloride, CH₂D³⁵Cl, was synthesized and investigated by Fourier transform infrared spectroscopy with an unapodized resolution of 0.004?cm^?1 in the range 650–900?cm^?1, the region of the lowest fundamentals ν₅ (827?cm^?1) and ν₆ (714?cm^?1). These distinct bands have been analysed in detail in the P-, Q- and R-branches. In spite of their expected a/b-hybrid nature, both envelopes show the peculiar characteristic of only a-type bands of near prolate asymmetric top molecules. Ground state parameters have been determined for the first time through ground state combination differences from both bands. Parameters of the excited vibrational states and coupling constants have been obtained using a model which accounts for c-type Coriolis interaction and ΔK_a?=?±?2 anharmonic resonance.     

Short-range order and its effect on the electronic structure of binary alloys: CuZn — a case study

We discuss an application of the generalized augmented space method introduced by one of us combined with the recursion method of Haydock et al (GASR) to the study of electronic structure and optical properties of random binary alloys. As an example, we have taken the 50-50 CuZn alloy, where neutron scattering indicates the existence of short-range order.      

Contribution to the study of the metal-insulator transition in the V1−xNbxO2 system: I — crystallographic and transport properties

The V_1−xNb_xO₂ system has been studied by X-ray diffraction as function of temperature and composition; as in earlier works three phases are shown to exist: a monoclinic phase which has the low temperature VO₂ structure, and two tetragonal phases, one having the rutile structure and the other the low temperature NbO₂ structure. Using D.T.A analysis, electrical conductivity and thermoelectric power data, we investigate the vanadium rich domain (x ≤ 0·50). In the low concentration region, (x < 0·10) we observe an electronic non-metal ⇄ metal transition close to the crystallographic transition, the transition temperature T_t decreasing when x increases. For large concentrations (x ≥ 0·15), the transition is broadened and occurs in a temperature range which increases with x; it becomes weaker and corresponds to the transition between two semi-conducting phases. At high temperature, a metal ⇄ non-metal transition occurs without structural changes, when x increases, near x = 0·12. A phase diagram is constructed for the VO₂-NbO₂ system with x < 0·15.