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The structures of melts containing cryolite have proved difficult to confirm, despite decades of study, on account of the high temperatures and corrosiveness of these melts. Raman spectroscopy has so far provided the majority of the insight into the aluminium coordination environments, but some of its interpretations are still debated. In this paper we present the results of MD simulations on various NaF-AlF3 liquid mixtures using published potentials developed for the solid state and published Raman spectra.

The assignments of the optical and vibrational spectra of bis(dicyano)croconate are proposed on the basis of the resonance Raman excitation profiles as well as semi-empirical calculations at the AM1 and PM3 levels. The absorption band at 532 nm is assigned to a p! p * transition, involving a molecular orbital delocalized over the pseudo-oxocarbon ring, whereas the one at 442 nm is assigned to a transition localized at the CN moieties. The calculation of the excitation profiles was performed using the transform method with a simple model of displaced harmonic oscillators, and in addition, the same model was used to reproduce the p ! p * absorption bandshape within the time-dependent formalism. q 1999 Elsevier Science B.V. All rights reserved.

The resonance Raman spectra of manganate(V) ion in aqueous solution in the visible and near-UV regions were studied. The maximum in the Raman excitation profile (REP) of the totally symmetric vibrational mode (ν1) at ca 600 nm is assigned to a charge-transfer transition with appreciable d–d character. Owing to marked orbital mixing in such systems, the observed Raman enhancement could also be assigned to a d–d transition with a high charge-transfer character. The absence of overtones in the Raman spectrum indicates a small shift in the equilibrium Mn—O bond distances (δr) between the excited and fundamental electronic states. This finding was confirmed by the calculation of the REP within the time formalism approach. The best fitted δr value is lower than the corresponding reported values for manganate(VII) and manganate(VI) ions. Two models were used in the calculations, in which whether a single or two electronic transitions were considered in the visible range of the absorption spectrum. Similar δr values were obtained with both models. Copyright © 1999 John Wiley & Sons, Ltd.

The fluctuating charge (FQ) model proposed by Rick et al. [(J. Chem. Phys. 101, 6141 (1994)] for molecular dynamics (MD) simulation of water is applied to a test case for polyatomic ionic systems. A system resembling alkali cyanide crystals, with two partial charges on the atomic sites of the polarizable anions, is considered. The need for charge fluctuation considerations in such a simple system is demonstrated by ab initio calculations of the partial charges in the cyanide ion with different orientations within a fixed octahedral environment of sodium ions. It is shown that the charge distributions in the crystal obtained with the FQ model are sensitive to changes in the environment in such a way that the anions become more polarizable as the lattice parameter increases. Conversely, the charge distributions shrink with increasing repulsive short-range interactions. Furthermore, a well-known polarization effect, that is, the reduction in the frequencies of longitudinal optic modes of the crystal, is also obtained with the FQ model.

A recently introduced polarizable-ion model for BeCl2 is compared to high quality ab initio calculations for the geometries of isolated chains [BeCl2] n . The relaxed geometries and vibrational frequencies (calculated using an instantaneous normal mode (INM) approach) are found to agree well. The density of states for the melt, calculated using the INMs, is shown to be very structured compared with typical molten salts, corresponding to a more ‘molecular’ spectrum. The band frequencies are seen to change little between the melt and the isolated chains further promoting the description of the liquid as an ensemble of such ‘polymeric’ chains. The calculated Raman spectrum is compared with experiment and shown to be fully consistent with the model as long as they are considered in terms of the symmetry of the molecular chains themselves. The dangers of assigning experimental bands in terms of the motions of local coordination polyhedra are emphasized.

We present a theoretical study with ab initio techniques on magnetic and electronic properties of 3d transition metal mononitrides. We perform the calculations in the wurtzite (w) and the zincblende (zb) structures, and find the tendency of all zb mononitrides to become half-metallic (HM) under hydrostatic strain. MnN, CrN, and VN become HM with integer magnetic moments of 4, 3 and 2μB, respectively. CrN shows ferromagnetism (FM) throughout the range of our lattice constant calculations, while VN is FM beyond the lattice constant of 4.65 A. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The dynamic structure factors, S(Q,ω), at a range of scattering vectors (Q) in the range 0.2

Indium was analyzed with both, standard differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) using sinusoidal and saw-tooth modulation. Instrument and sample effects were separated during nucleated, reversible melting and crystallization transitions, and irreversible crystallization with supercooling. The changes in heat flow, time, and sample and reference temperatures were correlated as functions of heating rate, mass, and modulation parameters. The transitions involve three regions of steady state (an initial and a final region before and after melting/crystallization, a region while melting/crystallization is in progress) and one region of approach to steady state (melting peak to final steady state region). Analyses in the time domain show promise when instrument lags, known from DSC, are used for correction of TMDSC. A new method of integral analysis is introduced for quantitative analysis even when irreversible processes occur in addition to reversible transitions. The information was derived from heat-flux calorimeters with control at the heater block or at the reference temperature sensor.

Fourier analysis of Raman bandshapes was undertaken for some modes of the lithium salts of squarate (C 4 O 4 2− ) and croconate (C 5 O 5 2− ) ions in saturated aqueous solution. Time correlation functions obtained from the isotropic and anisotropic Raman components of the totally symmetric modes of ring breathing, and the ones obtained from the anisotropic components of the non-totally symmetric modes of CC stretching and ring bending, have similar decay rates for both C 4 O 4 2− and C 5 O 5 2− , indicating that reorientation is very hindered in these systems for both spinning and tumbling of the main symmetry axis. The experimental vibrational correlation functions were fitted by the Kubo's equation, and are in the intermediate modulation regime, although faster than the ones for other typical ions reported in literature. The small time correlation of vibrational frequency fluctuations (≈ 0.1 ps) together with slow reorientation imply the picture of the ions performing librational motions inside temporary cages formed by water molecules. From the modeling of the vibrational and reorientational correlation functions, the estimated average librational frequency is ca. 80 cm −1 . Known models which separate homogeneous and inhomogeneous contributions give no better fitting of the vibrational correlation functions. The homogeneous nature of the vibrational dephasing process is also pointed by the almost perfect Lorentzian shape of the bands and by the calculation of the isotropic components by a memory function approach truncated in second order. Similar results were found after a 1:10 dilution of the saturated solutions, or upon increasing the temperature to 50°C, or yet by using of the sodium salts.

Vibrational dephasing of the ν 1 and ν 3 stretching modes of carbonyl sulfide, OCS, was investigated by computer simulations of the liquid in the states corresponding to 183, 243 and 273 K. Perturbation theory plus simulation of rigid molecules result in vibrational correlation functions which disagree with experimental ones. Systematic changes to other intermolecular potential and anharmonicity constants proposed in the literature show that dephasing in this system is more sensitive to modifications in the inter than in the intramolecular potential. In order to investigate possible flaws of the perturbation theory/rigid molecules simulation method, molecular dynamics considering fully flexible OCS molecules was undertaken for the liquid at 273 K. Even then, the slow decay of the vibrational correlation function points to the effective intermolecular potential, and not to the approximations involved in the rigid simulation method, as responsible for disagreements with available experimental data. The calculated increasing of vibrational frequencies in the liquid as compared to the gas phase values is not confirmed by the experiments, and indicates that the effective Lennard-Jones potential proposed in the literature is too much repulsive in predicting vibrational frequency shifts in liquid OCS.

Mutations in the p53 tumour suppressor gene are found at high frequency in bladder cancer. There is strong evidence that p53 plays an important role in controlling the cell cycle after DNA damage by ionizing radiation. However, the effect of loss of p53 function on radiosensitivity is not yet clear. Radiotherapy combined with chemotherapy is the most common treatment for patients with invasive bladder cancer. Recently three bladder cancer cell lines have been established and this paper investigates the p53 status and clonogenic survival of these cell lines following irradiation. It was found that one line expresses wt p53 (UCRU-BL-13) and two lines contain a codon 72 polymorphism (UCRU-BL-17 and UCRU-BL-28). UCRU-BL-17 cells also contain a point mutation affecting codon 280. The level of p53 expression in the cell lines is clearly different, with UCRU-BL-17 expressing a higher level of p53 compared with UCRU-BL-13; UCRU-BL-28 expressed intermediate levels. The clonogenic survival of these cell lines has been determined. It was found that the line expressing a p53 mutation was more sensitive than those with wild type p53, providing support for a model in which loss of p53 function is associated with increased radiosensitivity, possibly due to reduced p53-dependent DNA repair.

The long-standing question of the nature of the low-energy transition present in the optical spectrum of azo dyes was addressed by investigating the resonance Raman spectrum of 4-(2-pyridylazo)resorcinol (PAR). The Raman spectra were obtained at different pH values where the prevailing species are the monoanionic (HL-) or the dianionic (L2-) forms. The excitation profiles and absorption spectra were calculated satisfactorily using a single excited state as responsible for the low-energy transition present in the optical spectrum. The remarkably stable Cu(II) and Zn(II) chelates involving the coordination of the HL- species to the metal ions were also investigated, and again the excitation profiles and absorption spectra were calculated satisfactorily using a single excited state. In fact, the concerted use of the transform method and time-dependent theory indicates that the displacement parameters for the metal chelates are much more similar to those obtained for the L2- species than those for HL- species. In the case of the Cu(II) chelate, a long progression of overtones and combination bands was observed, which is uncommon for such an extended chromophore. Concerning the nature of the electronic transition responsible for the resonance enhancement, the extensive electronic delocalization of the chromophore and the complex composition of the normal modes preferentially enhanced must be noted. In other words, it is expected that the ππ* and nπ* states are thoroughly mixed in this class of the molecular systems. © 1997 by John Wiley & Sons, Ltd.

Hybrid organic-inorganic material containing Laponite clay and ionic liquids forming cations have been prepared and characterized by FT-Raman spectroscopy, X-ray diffraction, and thermal analysis. The effect of varying the length of the alkyl side chain and conformations of cations has been investigated by using different ionic liquids based on piperidinium and imidazolium cations. The structure of the N,N-butyl-methyl-piperidinium cation and the assignment of its vibrational spectrum have been further elucidated by quantum chemistry calculations. The X-ray data indicate that the organic cations are intercalated parallel to the layers of the clay. Comparison of Raman spectra of pure ionic liquids with different anions and the resulting solid hybrid materials in which the organic cations have been intercalated into the clay characterizes the local environment experienced by the cations in the hybrid materials. The Raman spectra of hybrid materials suggest that the local environment of all confined cations, in spite of this diversity in properties, resembles the liquid state of ionic liquids with a relatively disordered structure.

This paper is a review of the LDA(GGA)-1/2 method for band calculation. We review the many applications of the method: band gaps, semiconductor interfaces, semiconductor alloys. The number of applications where the method fails is minimal. Leading to results with a precision comparable to Hedin’s GW method, LDA-1/2 has the advantage of being orders of magnitude faster. The paper begins by a short theoretical review in which we try not repeat what is already published. Then we present some results that are scattered in the literature. We find that LDA(GGA)-1/2 is the recommended method for excited state energy calculations.

We studied the electronic properties of the AlP/GaP and AlN/GaN interfaces and their cubic constituents. The work is developed using approximate quasiparticle approach LDA-1/2 method. First, we provide a detailed calculation of bulk AlN, AlP, GaN, and GaP. In addition to accurate results for fundamental band gap, we also obtained accurate electronic transition levels along valence and conduction bands profiles, compared to experiments and theoretical results using GW and hybrid functionals methods. For the conduction (valence) band offset we obtained 0.27 eV (0.43 eV) for AlP/GaP and 1.47 eV (0.36 eV) for AlN/GaN interfaces, in good agreement with experimental results.

International audience; Raman spectra in the range of the totally symmetric stretching mode of the [PF6 ]− anion, νs (PF6 ), have been measured for 1-alkyl-3-methylimidazolium ionic liquids [Cn C1 im][PF6 ], for n = 4, 6, and 8, as a function of pressure at room temperature. The ionic liquids [C6 C1 im][PF6 ] and [C8 C1 im][PF6 ] remain in an amorphous phase up to 3.5 GPa, in contrast to [C4 C1 im][PF6 ], which crystallizes above ∼0.5 GPa. Equations of state based either on a group contribution model or Carnahan-Starling-van der Waals model have been used to estimate the densities of the ionic liquids at high pressures. The shifts of the vibrational frequency of νs (PF6 ) with density observed in [C6 C1 im][PF6 ] and in [C8 C1 im][PF6 ] have been calculated by a hard-sphere model of a pseudo-diatomic solute under short-range repulsive interactions with the neighboring particles. The stochastic model of Kubo for vibrational dephasing has been used to obtain the amplitude of vibrational frequency fluctuation, (,6.ω2 ), and the relaxation time of frequency fluctuation, τ c , as a function of density by Raman band shape analysis of the νs (PF6 ) mode of [C6 C1 im][PF6 ] and [C8 C1 im][PF6 ].

The understanding of the denaturation process in proteins still constitutes an obscure matter. Most of the mechanisms proposed for protein denaturation promoted by chemical agents, such as urea, have focused on the direct interaction of the denaturant molecules with the peptide groups of the protein backbone, modifying the pattern of hydrogen bonds that stabilize the protein specific folding (1–4). In another perspective of the problem, physico-chemical data have provided insights into the role of water structure in the process (5). We have undertaken a vibrational Raman study of aqueous solutions of protein denaturants in the presence of a well characterized protein, namely, chiken egg lysozyme. A formalism of band shape analysis has been applied to the v4 band of urea, to determine its vibrational and reorientatinal correlation functions (6) and their dependence on the presence of lysozyme. The formalism employed is that described by Rothschild (7), which is based on Kubo’s stochastic line shape theory. The water band in the presence of denaturants has also been investigated. The vibrational modes of water involve a rather complex description as a consequence of inter and intramolecular couplings, and also, possibly, of Fermi resonance. In the present work, we have applied a methodology that allows the analysis of the decoupled OD stretching vibration in D2O/H2O mixtures (8).

Vibrational dephasing of the totally symmetric stretching mode of liquid carbon disulfide at different pressures at room temperature is investigated by molecular dynamics simulation. The thermodynamic states simulated correspond to the liquid at atmospheric pressure, 1 kbar, 4 kbar and 8 kbar, all at room temperature (294 K). An - effective vibrational-rototranslational coupling potential, which contains an exponential repulsive term and an attractive long range term, is assumed. The fundamental role of anisotropy in this potential is emphasized. The experimental trend of average gas-to-liquid vibrational frequency shifts and vibrational correlation functions are well reproduced by molecular dynamics. The simulations show that correlation functions of vibrational frequency fluctuation of CS2 are not a single exponential, what invalidates the well-known Kubo's formula for vibrational correlation function. The long time behaviour seen in the frequency fluctuation correlation functions, present even if one assumes a purely repulsive, short range coupling potential, is due to the characteristic hindrance of the rototranslational dynamics of CS2. The simulations also show a small correlation between vibrational and reorientational relaxations, even when an isotropic coupling potential is considered, what is an indication of coupling between vibrational and reorientational degrees of freedom by translational motions.

Computer simulation of vibrational dephasing of liquid CS2 indicates that the correlation function of frequency fluctuation is not a single exponential, which invalidates the use of Kubo's formula for the vibrational correlation function. The two different time scales for the decay of the frequency fluctuation correlation function allow one to propose a double-exponential model for the memory function of the vibrational correlation function. The model is used to fit vibrational correlation functions obtained from molecular dynamics of CS2 at 1 bar, 1kbar and 4kbar at room temperature. The hindrance of the rotational and translational dynamics under high pressures results in a larger contribution from the slow decay term of the frequency fluctuation correlation functions and memory functions.

Resonant Raman spectra of the square planar complexes [Bu 4 N][M(dbt) 2 ] (M = Ni, Co, Cu; bdt = 1,2-benzenedithiolate; Bu = butyl) have been obtained with a variety of excitation lines. In all cases a strong band at about 400 nm is now definitely assigned to a ligand-to-metal charge transfer (LMCT) transition on the basis of the observed pre-resonance enhancement of modes assignable to the metal-sulphur chromophore. For the cobalt species, an additional strong band at about 670 nm is observed and is assigned to another CT transition on the basis of the enhancement of modes related to the CCS moiety, such proposal being supported by calculations based on the transform method.

The separation of the Raman correlation function as a product of independent vibrational and reorientational correlation functions is investigated. The present model is a unification of previous models which treat separately vibrational dephasing and reorientational relaxation within the context of the stochastic approach. It indicates that the so-called product approximation for the Raman correlation function can fail even when the relaxation rate is distinct for vibrational and reorientational relaxations. Application to experimental data for liquid CS2 is presented.

The decision version of the Max-Cut problem was proved to be NP-complete by Karp and remains NP-complete even in the unaligned case. It has found wide application, including VLSI design and statistical physics. In this paper, we study GRASP and VNS heuristics for Max-Cut, together with a combination of the two in a hybrid procedure.

Ionic liquids based on 1-alkyl-3-methylimidazolium cations and the hydrogen sulfate (or bisulfate) anion, HSO(4)(-), are much more viscous than ionic liquids with alkyl sulfates, RSO(4)(-). The structural origin of the high viscosity of HSO(4)(-) ionic liquids is unraveled from detailed comparison of the anion Raman bands in 1-ethyl-3-methylimidazolium hydrogen sulfate and 1-butyl-3-methylimidazolium hydrogen sulfate with available data for simple HSO(4)(-) salts in crystalline phase, molten phase, and aqueous solution. Two Raman bands at 1046 and 1010 cm(-1) have been assigned as symmetric stretching modes ν(s)(S═O) of HSO(4)(-), the latter being characteristic of chains of hydrogen-bonded anions. The intensity of this component increases in the supercooled liquid phase. For comparison purposes, Raman spectra of 1-ethyl-3-methylimidazolium ethyl sulfate and 1-butyl-3-methylimidazolium methyl sulfate have been also obtained. There is no indication of difference in the strength of hydrogen bond interactions of imidazolium cations with HSO(4)(-) or RSO(4)(-) anions. Raman spectra at high pressures, up to 2.6 GPa, are also discussed. Raman spectroscopy provides evidence that hydrogen-bonded anions resulting in anion-anion interaction is the reason for the high viscosity of imidazolium ionic liquids with HSO(4)(-). If the ionic liquid is exposed to moisture, these structures are disrupted upon absorption of water from the atmosphere.

Molecular dynamics simulations have been performed for ionic liquids based on a ternary mixture of lithium and ammonium cations and a common anion, bis(trifluoromethylsulfonyl)imide, [Tf(2)N](-). We address structural changes resulting from adding Li(+) in ionic liquids with increasing length of an ether-functionalized chain in the ammonium cation. The calculation of static structure factors reveals the lithium effect on charge ordering and intermediate range order in comparison with the neat ionic liquids. The charge ordering is modified in the lithium solution because the coordination of [Tf(2)N](-) toward Li(+) is much stronger than ammonium cations. Intermediate range order is observed in neat ionic liquids based on ammonium cations with a long chain, but in the lithium solutions, there is also a nonhomogenous distribution of Li(+) cations. The presence of Li(+) enhances interactions between the ammonium cations due to correlations between the oxygen atom of the ether chain and the nitrogen atom of another ammonium cation.

The time-dependent theory of the resonance Raman effect was employed for the calculation of the Raman excitation profiles and optical absorption spectra of the meial dithiolene species [Zn(dmit)2]2− and [Ni(dmit)2]2− (dmit = 4,5-dimercapto-1,3-dithiolc-2-thionc) The model adopted takes into account the three normal modes notable for their enhancement at resonance, and embodies the linear non-Condon coupling contribution. Previous calculations for these species using the transform method lead to estimates of the relative displacements of potential surface minima for the three modes considered, while the present calculations led to absolute values for such displacements. The metal-sulphur bond length is increased by 0.016 and 0.027 A in the zinc and nickel complexes, respectively.

Molecular dynamics simulations were performed for ionic liquids based on the bis(trifluoromethylsulfonyl)imide anion, [NTf(2)], and ammonium cations with increasing length of the alkyl chain and ether functionalized chain. The signature of charge ordering is a sharp peak in the charge-charge structure factor, S(qq)(k), whose intensity is barely affected for longer carbon chain in tetraalkylammonium systems, but decreases in ether functionalized ionic liquids. The first sharp diffraction peak (FSDP) and the corresponding intermediate range order (IRO) are observed in the total S(k) of ionic liquids containing ammonium cations with relatively long chains. The intensity of the FSDP is lower in the total S(k) of the ether derivative in comparison with the tetraalkylammonium counterpart of the same chain length. It is shown that the nature of the IRO is structural heterogeneity of polar and non-polar domains, even though domains defined by chain interactions in the ether derivatives become more polar. Charge correlation in the ether derivative is modified because cations can be coordinated by oxygen atoms of the ether functionalized chain of neighboring cations.

Molecular dynamics (MD) simulations of the glass-former 2Ca(NO(3))(2·3KNO(3), CKN, were performed as a function of temperature at pressures 0.1 MPa, 0.5 GPa, 1.0 GPa, and 2.0 GPa. Diffusion coefficient, relaxation time of the intermediate scattering function, and anion reorientational time were obtained as a function of temperature and densitiy ρ. These dynamical properties of CKN scale as ρ(γ)∕T with a common value γ = 1.8 ± 0.1. The scaling parameter γ is consistent with the exponent of the repulsive part of an effective intermolecular potential for the repulsion between the atoms at shortest distance in the equilibrium structure of liquid CKN, Ca(2+), and oxygen atoms of NO(3)(-). Correlation between potential energy and virial is obeyed for the short-range terms of the potential function, but not for the whole potential including coulombic interactions. Decoupling of diffusion coefficient and reorientational relaxation time from relaxation time take place at a given ρ(γ)∕T value, i.e., breakdown of Stokes-Einstein and Debye-Stokes-Einstein equations result from combined thermal and volume effects. The MD results agree with correlations proposed between long-time relaxation and short-time dynamics, lnτ ∝ 1∕u(2), where the mean square displacementu(2)concerns a time window of 10.0 ps. It has been found thatu(2)scales as ρ(γ)∕T above and below the glass transition temperature, so that thermodynamic scaling of liquid dynamics can be thought as a consequence of theories relating short- and long-time dynamics, and the more fundamental scaling concerns short-time dynamical properties.

Many experiments that aim at the direct detection of Dark Matter are able to distinguish a dominant background from the expected feeble signals, based on some measured discrimination parameter. We develop a statistical model for such experiments using the Profile Likelihood ratio as a test statistic in a frequentist approach. We take data from calibrations as control measurements for signal and background, and the method allows the inclusion of data from Monte Carlo simulations. Systematic detector uncertainties, such as uncertainties in the energy scale, as well as astrophysical uncertainties, are included in the model. The statistical model can be used to either set an exclusion limit or to make a discovery claim, and the results are derived with a proper treatment of statistical and systematic uncertainties. We apply the model to the first data release of the XENON100 experiment, which allows to extract additional information from the data, and place stronger limits on the spin-independent elastic WIMP-nucleon scattering cross-section. In particular, we derive a single limit, including all relevant systematic uncertainties, with a minimum of 2.4x10^-44 cm^2 for WIMPs with a mass of 50 GeV/c^2., 8 pages, 6 figures, matches accepted version

The XENON100 experiment, located at the Laboratori Nazionali del Gran Sasso (LNGS), aims to directly detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off xenon nuclei. We present a comprehensive study of the predicted electronic recoil background coming from radioactive decays inside the detector and shield materials, and intrinsic contamination. Based on GEANT4 Monte Carlo simulations using a detailed geometry together with the measured radioactivity of all detector components, we predict an electronic recoil background in the WIMP-search energy range (0-100 keV) in the 30 kg fiducial mass of less than 10e-2 events/(kg-day-keV), consistent with the experiment's design goal. The predicted background spectrum is in very good agreement with the data taken during the commissioning of the detector, in Fall 2009., 10 pages, 12 figures The updated version of the paper takes into account the new measurement of $^{136}$Xe 2$\nu$ $\beta\beta$ decay by EXO-200, with a half-life of (2.11$\pm0.04\pm$0.021)$\times10^{21}$ years

The transform method is employed to reproduce the Raman excitation profiles of the ν 1 , 2ν 1 , and 3ν 1 Raman bands, as well as those of the anti-Stokes components -ν 1 , and -2ν 1 of titanium tetraiodide in cyclohexane solution. The theoretical fit of the profiles was achieved with a unique set of physical parameters; in particular, the line-shape fitting was based exclusively on the linear non-Condon to linear vibronic coupling ratio, m/ξ, that optimizes at 0.055±0.005. The use of a different vibrational frequency in the excited electronic state does not improve the fit at any extent. From the fit of the relative intensities of the profiles, an absolute value of ξ=3.7±0.1 was obtained, leading to a Ti-I bond-length variation in the excited electronic state of 0.105 A

The use of the transform method was extended so as to permit the treatment of the resonance Raman effect with the participation of two interfering electronic transitions. The relevant equations were tested in the model system [Ru(bipy) 2 (violurate)]PF 6 , the Raman excitation profiles of which show clearly the presence of two chromophoric moieties. The present results strongly suggest that the two relevant excited states participate by means of Albrecht's A terms, whereas the vibronic coupling by the B term is not decisive. The independence of the two chromophoric moieties is reflected in distinct displacements of the respective potential minima

Raman spectra within the 5-200 cm(-1) range have been recorded as a function of temperature for different ionic liquids based on imidazolium cations. A correlation has been found between fragility and the temperature dependence of the strength of fast relaxational motions. Understanding quasielastic scattering as the relaxational contribution to ionic mean-squared displacement elucidates some effects on ionic liquids' fragility resulting from modifications in the chemical structure.

The addition of lithium salts to ionic liquids causes an increase in viscosity and a decrease in ionic mobility that hinders their possible application as an alternative solvent in lithium ion batteries. Optically heterodyne-detected optical Kerr effect spectroscopy was used to study the change in dynamics, principally orientational relaxation, caused by the addition of lithium bis(trifluoromethylsulfonyl)imide to the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Over the time scales studied (1 ps-16 ns) for the pure ionic liquid, two temperature-independent power laws were observed: the intermediate power law (1 ps to approximately 1 ns), followed by the von Schweidler power law. The von Schweidler power law is followed by the final complete exponential relaxation, which is highly sensitive to temperature. The lithium salt concentration, however, was found to affect both power laws, and a discontinuity could be found in the trend observed for the intermediate power law when the concentration (mole fraction) of lithium salt is close to chi(LiTf(2)N) = 0.2. A mode coupling theory (MCT) schematic model was also used to fit the data for both the pure ionic liquid and the different salt concentration mixtures. It was found that dynamics in both types of liquids are described very well by MCT.

The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso in Italy, is designed to search for dark matter WIMPs scattering off 62 kg of liquid xenon in an ultra-low background dual-phase time projection chamber. In this letter, we present first dark matter results from the analysis of 11.17 live days of non-blind data, acquired in October and November 2009. In the selected fiducial target of 40 kg, and within the pre-defined signal region, we observe no events and hence exclude spin-independent WIMP-nucleon elastic scattering cross-sections above 3.4 x 10^-44 cm^2 for 55 GeV/c^2 WIMPs at 90% confidence level. Below 20 GeV/c^2, this result constrains the interpretation of the CoGeNT and DAMA signals as being due to spin-independent, elastic, light mass WIMP interactions., 5 pages, 5 figures. Matches published version

An alternative method for determination of total trans fatty acids expressed as elaidic acid by capillary zone electrophoresis (CZE) under indirect UV detection at 224 nm within an analysis time of 7.5 min was developed. The optimized running electrolyte includes 15.0 mmol L(-1) KH(2)PO(4)/Na(2)HPO(4) buffer (pH approximately 7.0), 4.0 mmol L(-1) SDBS, 8.0 mmol L(-1) Brij35, 45%v/v ACN, 8% methanol, and 1.5% v/v n-octanol. Baseline separation of the critical pair C18-9cis/C18:1-9t with a resolution higher than 1.5 was achieved using C15:0 as the internal standard. The optimum capillary electrophoresis (CE) conditions for the background electrolyte were established with the aid of Raman spectroscopy and experiments of a 3(2) factorial design. After response factor (R(F)) calculations, the CE method was applied to total trans fatty acid (TTFA) analysis in a hydrogenated vegetable fat (HVF) sample, and compared with the American Oil Chemists' Society (AOCS) official method by gas chromatography (GC). The methods were compared with an independent sample t test, and no significant difference was found between CE and GC methods within the 95% confidence interval for six genuine replicates of TTFA analysis (p-value0.05). The CE method was applied to TTFA analysis in a spreadable cheese sample. Satisfactory results were obtained, indicating that the optimized methodology can be used for trans fatty acid determination for these samples.

The ionic liquids (ILs) 1-ethoxyethyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, [EtO(CH(2))(2)MMI][Tf(2)N], and N-(ethoxyethyl)-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide, [EtO(CH(2))(2)MMor][Tf(2)N] were synthesized, and relevant properties, such as thermal stability, density, viscosity, electrochemical behavior, ionic conductivity, and self-diffusion coefficients for both ionic species, were measured and compared with those of their alkyl counterparts, 1-n-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, [BMMI][Tf(2)N], and N-n-butyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide, [BMP][Tf(2)N] and N-n-butyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide [BMMor][Tf(2)N]. This comparison was done to evaluate the effects caused by the presence of the ether bond in either the side chain or in the organic cation ring. The salt, LiTf(2)N, was added to the systems to estimate IL behavior with regard to lithium cation transport. Pure [EtO(CH(2))(2)MMI][Tf(2)N] and their LiTf(2)N solutions showed low viscosity and the highest conductivity among the ILs studied. The H(R) (AC conductivity/NMR calculated conductivity ratio) values showed that, after addition of LiTf(2)N, ILs containing the ether bond seemed to have a greater number of charged species. Structural reasons could explain these high observed H(R) values for [EtO(CH(2))(2)MMor][Tf(2)N].

The nature of the electronic transitions present in the optical spectra of the 4,5-dimercapto-1,3-dithiole-2-thione (H 2 dmit) complexes [Ni(dmit) 2 ] 2− and [Zn(dmit) 2 ] 2− was investigated by resonance Raman spectroscopy, supported by the transform method. The previous assignment proposed for the 515 nm band in [Zn(dmit) 2 ] 2− is shown to be incorrect, and the intrinsically different nature of the charge-transfer transitions in [Zn(dmit) 2 ] 2− and [Ni(dmit) 2 ] 2− is revealed by the excitation profiles and by the parameters obtained from the use of the transform method.

The present work describes the crystal structure, vibrational spectra, and theoretical calculations of ammonium salts of 3,5-bis-(dicyanomethylene)cyclopentane-1,2,4-trionate, (NH(4))(2)(C(11)N(4)O(3)) [(NH(4))(2)CV], also known as ammonium croconate violet. This compound crystallizes in triclinic P1 and contains two water molecules per unit formula. The crystal packing is stabilized by hydrogen bonds involving water molecules and ammonium cations, giving rise to a 3D polymeric arrangement. In this structure, a pi-stacking interaction is not observed, as the smaller centroid-centroid distance is 4.35 A. Ab initio electronic structure calculations under periodic boundary conditions were performed to predict vibrational and electronic properties. The vibrational analysis was used to assist the assignments of the Raman and infrared bands. The solid structure was optimized and characterized as a minimum in the potential-energy surface. The stabilizing intermolecular hydrogen bonds in the crystal structure were characterized by difference charge-density analysis. The analysis of the density of states of (NH(4))(2)CV gives an energy gap of 1.4 eV with a significant contribution of carbon and nitrogen 2p states for valence and conduction bands.

The viscosity of ionic liquids based on quaternary ammonium cations is reduced when one of the alkyl chains is replaced by an alkoxy chain ( Zhou et al. Chem. Eur. J. 2005 , 11 , 752. ). A microscopic picture of the role played by the ether function in decreasing the viscosity of quaternary ammonium ionic liquids is provided here by molecular dynamics (MD) simulations. A model for the ionic liquid N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, MOENM(2)E TFSI, is compared to the tetraalkylammonium counterpart. The alkoxy derivative has lower viscosity, higher ionic diffusion coefficients, and higher conductivity than the tetraalkyl system at the same density and temperature. A clear signature of the ether function on the liquid structure is observed in cation-cation correlations, but not in anion-anion or anion-cation correlations. In both the alkyl and the alkoxy ionic liquids, there is aggregation of long chains of neighboring cations within micelle-like structures. The MD simulations indicate that the less effective assembly between the more flexible alkoxy chains, in comparison to alkyl chains, is the structural reason for higher ionic mobility in MOENM(2)E TFSI.

Lithium salt solutions of Li(CF3SO2)2N, LiTFSI, in a room-temperature ionic liquid (RTIL), 1-butyl-2,3-dimethyl-imidazolium cation, BMMI, and the (CF3SO2)2N(-), bis(trifluoromethanesulfonyl)imide anion, [BMMI][TFSI], were prepared in different concentrations. Thermal properties, density, viscosity, ionic conductivity, and self-diffusion coefficients were determined at different temperatures for pure [BMMI][TFSI] and the lithium solutions. Raman spectroscopy measurements and computer simulations were also carried out in order to understand the microscopic origin of the observed changes in transport coefficients. Slopes of Walden plots for conductivity and fluidity, and the ratio between the actual conductivity and the Nernst-Einstein estimate for conductivity, decrease with increasing LiTFSI content. All of these studies indicated the formation of aggregates of different chemical nature, as it is corroborated by the Raman spectra. In addition, molecular dynamics (MD) simulations showed that the coordination of Li+ by oxygen atoms of TFSI anions changes with Li+ concentration producing a remarkable change of the RTIL structure with a concomitant reduction of diffusion coefficients of all species in the solutions.

Molecular dynamics simulations of the glass-forming liquid 2Ca(NO3)2.3KNO3 (CKN) were performed from high temperature liquid states down to low temperature glassy states at six different pressures from 10(-4) to 5.0 GPa. The temperature dependence of the structural relaxation time indicates that the fragility of liquid CKN changes with pressure. In line with recent proposal [Scopigno et al., Science 302, 849 (2003)], the change on liquid fragility is followed by a proportional change of the nonergodicity factor of the corresponding glass at low temperature.

Dynamical properties of polymer electrolytes based on poly(ethylene oxide) (PEO) and ionic liquids of 1-alkyl-3-methylimidazolium cations were calculated by molecular dynamics simulations with previously proposed models [L. T. Costa and M. C. Ribeiro, J. Chem. Phys. 124, 184902 (2006)]. The effect of changing the ionic liquid concentration, temperature, and the 1-alkyl-chain lengths, [1,3-dimethylimidazolium]PF(6) and [1-butyl-3-methylimidazolium]PF(6) ([dmim]PF(6) and [bmim]PF(6)), was investigated. Cation diffusion coefficient is higher than those of anion and oxygen atoms of PEO chains. Ionic mobility in PEO[bmim]PF(6) is higher than in PEO[dmim]PF(6), so that the ionic conductivity kappa of the former is approximately ten times larger than the latter. The ratio between kappa and its estimate from the Nernst-Einstein equation kappa/kappa(NE), which is inversely proportional to the strength of ion pairs, is higher in ionic liquid polymer electrolytes than in polymer electrolytes based on inorganic salts with Li(+) cations. Calculated time correlation functions corroborate previous evidence from the analysis of equilibrium structure that the ion pairs in ionic liquid polymer electrolytes are relatively weak. Structural relaxation at distinct spatial scales is revealed by the calculation of the intermediate scattering function at different wavevectors. These data are reproduced with stretched exponential functions, so that temperature and wavevector dependences of best fit parameters can be compared with corresponding results for polymer electrolytes containing simpler ions.

Low-frequency (5-200 cm(-1)) Raman spectra are reported for the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim]PF(6), in glassy, supercooled liquid, and normal liquid phases (77-330 K). Raman spectra of [bmim]PF(6) agree with previous results obtained by optical Kerr effect spectroscopy and molecular dynamics simulation. Both the superposition model and the coupling model give reasonable fit to low-frequency Raman spectra of [bmim]PF(6). The configurational entropy of [bmim]PF(6) has been evaluated as a function of temperature using recently reported data of heat capacity. The calculated configurational entropy is inserted in the Adam-Gibbs theory for supercooled liquids, giving a good fit to non-Arrhenius behavior of viscosity and diffusive process, with the latter revealed by a recent neutron scattering investigation of [bmim]PF(6). There is a remarkable linear dependence between intensity of quasielastic Raman scattering and configurational entropy from 77 K up to the melting point of [bmim]PF(6). This correlation offers insight into the nature of dynamical processes probed by low-frequency Raman spectra of ionic liquids.

We present an ab initio tooled study on magnetic and electronic properties of 3d transition metals mononitrides under hydrostatic and biaxial strain, in wurtzite (w) and zincblende (zb) structure, and find all of them to become half‐metallic (HM) under lattice expansion in the zb structure. The first compound to become HM under lattice expansion is MnN, followed by CrN, VN, FeN and CoN, with integer magnetic moments of 4, 3, 2, 5 and 6 μB, respectively. We investigate the possibility of MBE growing of zb‐CrN on cubic GaN.

The influence of the substrate electrochemical pre-treatment in 0.5 mol L-1 H2SO4 on the Pt electrodeposition on boron-doped diamond, BDD, film electrodes was investigated. Platinum cannot be electrodeposited on a freshly prepared BDD electrode; however, potentiodynamic cycling or anodic potential steps at short times does activate the electrode. Anodic pre-treatment plays a dual role in the behavior of Pt deposition on BDD surfaces: Pt deposition is increased at short-term anodic pre-treatments, whereas at longer pre-treatment times Pt deposition was inhibited. These facts are explained in terms of wettability changes and passivation of the surface. Conversely, the oxide layer formed in these treatments increases the dispersion level of the catalyst. Este trabalho trata da influência do pré-tratamento eletroquímico de eletrodos de diamante dopado com boro (DDB) em meio ácido, na eletrodeposição de platina. Pt não pôde ser eletrodepositada em eletrodos de DDB recém-preparados. Entretanto, pré-tratamentos baseados em varreduras de potenciais ou em polarizações anódicas a potencial constante em curtos intervalos de tempo ativaram o eletrodo para a deposição de Pt. O tratamento anódico desempenha diferentes papéis, de acordo com o tempo de tratamento: em tempos curtos, a deposição de Pt é aumentada, ao passo que tempos de polarização mais longos inibem o processo de eletrodeposição de Pt, originando, entretanto, depósitos com maior área superficial. Tais resultados são discutidos em termos de mudanças na hidrofilicidade da superfície do DDB, bem como na apassivação da superfície, provavelmente representada pela oxidação da mesma.

Molecular dynamics (MD) simulations have been performed for prototype models of polymer electrolytes in which the salt is an ionic liquid based on 1-alkyl-3-methylimidazolium cations and the polymer is poly(ethylene oxide), PEO. The MD simulations were performed by combining the previously proposed models for pure ionic liquids and polymer electrolytes containing simple inorganic ions. A systematic investigation of ionic liquid concentration, temperature, and the 1-alkyl- chain length, [1,3-dimethylimidazolium]PF6, and [1-butyl-3-methylimidazolium]PF6, effects on resulting equilibrium structure is provided. It is shown that the ionic liquid is dispersed in the polymeric matrix, but ionic pairs remain in the polymer electrolyte. Imidazolium cations are coordinated by both the anions and the oxygen atoms of PEO chains. Probability density maps of occurrences of nearest neighbors around imidazolium cations give a detailed physical picture of the environment experienced by cations. Conformational changes on PEO chains upon addition of the ionic liquid are identified. The equilibrium structure of simulated systems is also analyzed in reciprocal space by using the static structure factor, S(k). Calculated S(k) display a low wave-vector peak, indicating that spatial correlation in an extended-range order prevail in the ionic liquid polymer electrolytes. Long-range correlations are assigned to nonuniform distribution of ionic species within the simulation box.