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Rotational and rotovibrational spectra of fluid N2 at T = 119 K and ρ = 570 and 625 amagatare reported. Substantial agreement is found with a recent molecular dynamics simulation which takes into account all dipole–induced-dipole effects including the cross interference term betwen permanent and induced anisotropy. A procedure is described to derive the nonrotational contribution from the experimental spectra using a rotational model spectrum based on a parametrized memory function.The derived lineshapes (collision induced plus cross term) are in agreement with molecular dynamics results.

Orientational correlation functions derived from the rotational and rotovibrational Raman spectra of N2 at 150 K and 585 amagat are compared with the results of a molecular dynamics simulation available in the literature. The angular momentum correlation function is also estimated from the experimental memory function and compared with the one obtained by simulation. Mean square torques, intermolecular correlations and interaction induced contributions are also discussed.

Rotational Raman spectra for an accidentally or nearly symmetric rotor are discussed in detail. The spectral-moment theory is used to yield expressions for the polarizability invariants and for the different orientational correlation times involved. A generalization of Gordon'sJ-diffusion is presented which is able to reproduce also spectra in which the quantization of the rotational states is still present. A further generalization of the model is suggested to account for the molecular anisotropy during the collision process.

A comparison is made between the rotovibrational Raman bands of fluid nitrogen at room temperature in the 180–355 amagat density range and the corresponding pure rotational bands reported previously. Accurate moment values are derived from the Raman spectra, accounting for the response of the entire experimental apparatus, after subtraction of the unwanted isotope band and of the leaking polarized Q branch. Correlation times are also calculated for both rotovibrational and pure rotational spectra accounting for the finite instrumental slitwidth. Intermolecular torques and orientational correlation times derived from the two spectra are in good agreement for almost the entire available density range. Small discrepancies, particularly evident in the low density correlation times, are discussed and related to the rotation-vibration interaction. Intermolecular correlations are found to be negligible.

The Raman scattering cross-section in molecular systems is calculated with the aim of accounting for the low frequency spectrum of disordered media. It is shown that, as far as translational motions are concerned, the isotropic polarizability correlation function is not strongly affected by the structural disorder and is essentially determined by the density-density correlation function. In contrast the anisotropic term depends strongly on the disorder of the system. Its contribution to the scattered light spectrum is governed by single molecule dynamics, thus reflecting in some cases the entire density of translational states, while the intensity is determined by the rotational—translational coupling.

Polarized and depolarized Raman spectra in the translational and librational region of liquid water and heavy water have been measured as a function of temperature. A detailed analysis of the isotropic spectrum is performed. This component, which cannot arise from any 'allowed' molecular contribution in this frequency region, shows two distinct spectral features which can be obtained from an analysis of temperature dependent lineshapes. The first one, which dominates the spectrum up to 500crn-1, shows on the basis of a H20-DzO comparison a translational behaviour at very low frequency and a librational one at higher frequencies. It is assigned on the basis of its frequency profile, of its absolute intensity and of its temperature dependence to rototranslational spectra due to long range induction mechanisms already found in many molecular liquids. The second one, which is peaked at roughly 800 cm-1 in water and extends up to the bending mode region suggests the existence of a short range interaction induced polarizability.

We have derived an expression for the light scattering spectrum of a crystal in which the mechanically regular sites are occupied by point polarizable orientationally disordered molecules when the polarizabilities are assumed to depend on the positions of the surrounding atoms (interaction induced polarizability fluctuations). Owing to the ‘electrical’ disorder properties of the system all phonons can contribute to the anisotropic scattering measured in all polarization configuration with wavevector, branch index and polarization dependent coefficients. Assuming short range interaction induced polarizabilities we show that the temperature reduced intensity I(ω)/[n(ω) + 1] is given by a superposition of the Brillouin zone centre symmetry ‘projected’ density of states with polarization dependent coefficients. These coefficients are found to be essentially frequency independent for all the projections, exception made for those corresponding to the acoustic phonons. For the acoustic branches the coefficients ...

The interpretation of light scattering spectra in disordered solids is from many aspects, an incompletely solved problem, expecially when it is desired to extract from the spectra information about the dynamics of the particles of the system. In this paper, we outline a formalism that can be easily applied to disordered molecular solids, and which can be extensively used in several other cases, even for some liquid samples when certain conditions are satisfied. This formalism is then applied to two particular cases of partially disordered crystals: α-AgI and Ice Ih. In both cases the relation between Raman scattering lineshapes and the densities of vibrational states is clarified; acoustic and optic phonon densities of states are derived and compared with neutron scattering experiments. The results are encouraging and suggest further applications of the formalism.

Deep inelastic neutron-scattering measurements have been performed in dense fluid ${}^{4}\mathrm{He}$ along three iso- chores at number densities $33$, $38$, and $45 {\mathrm{nm}}^{\ensuremath{-}3}$ and temperatures ranging from $4.35$ to $56 \mathrm{K}$. Data have been analyzed in the plane-wave impulse-approximation framework to obtain the root-mean-square values of the single-particle momentum along a given direction ${p}_{x}.$ The density and temperature behavior of the derived mean kinetic energies is discussed in comparison with a simple harmonic model for the fluid and with quantum simulations performed using a path-integral Monte Carlo code. The comparison with the harmonic models sheds light on the density dependence of the zero-point kinetic energy of the particles and points out the inadequacy of a single-frequency Einstein-oscillator model in describing its temperature dependence. The quantum simulation results are in substantial agreement with the experimental data although systematic deviations are found as the density is increased.

Neutron diffraction measurements on fluid CO2 in a wide thermodynamic range covering both undercritical and supercritical states are presented. From these measurements, performed using 7C2 spectrometer at the Orphee reactor, we have derived the experimental neutron weighted radial distribution functions g(r). Moreover, for each investigated thermodynamic state, we performed molecular dynamics simulations from which the various molecular pair distribution functions g( R, Ω 1 , Ω 2 ) have been calculated, thus gaining a detailed information on the microscopic structure of the fluid, particularly on the orientational correlations. The main results, valid for all investigated densities and temperatures, are that: o 1. (i) Fluid CO2 shows significant orientational correlations only among first neighbor molecules; such correlations become less pronounced as the temperature increases although they are still quite evident up to 1.56 times the critical temperature and density down to 0.76 times the triple point density. 2. (ii)T-shaped local configurations are found to be favored. 3. (iii)The inclusion of electric quadrupole interactions in the intermolecular pair potential is essential in order to obtain agreement between Molecular Dynamics simulations and experimental g(r). The electric quadrupole interaction is also the origin of the predominance of T-shaped local configurations.

Diabetes mellitus (DM) and periodontal disease (PD) are both chronic diseases. From one side, DM have an adverse effect on PD, and on the other side PD may influence DM. Systemic therapy of DM with glycaemic control, affects the progress of PD. Reversely treatment of PD combined with the administration of systemic antibiotics seems to have a double effect on diabetic patients reducing the periodontal infection and improving the glycaemic control. Inflammation, altered host responses, altered tissue homeostasis are common characteristic of both DM and PD. The potential common pathophysiologic pathways of direct or reverse relationship of DM and PD are still unknown and further

Raman spectra have been collected in iodine single crystal at room temperature in the pressure range 1-14 GPa using a micro-Raman apparatus. The pressure at the sample was generated by means of a diamond anvil cell. Single crystals were grown in situ over the inner diamond surface. A careful analysis of the frequencies and intensities of internal (stretching) and external (libration) modes as a function of the pressure is reported. In particular, analysis of the relative intensities of the Raman modes confirms a theoretical prediction about the pressure evolution of the A g stretching mode eigenvector and the huge intensity increase of the external modes with respect to the internal ones is well consistent with the predicted increased role of the charge-transfer interaction when approaching the metallization transition pressure. At pressures higher than 10 GPa, spectral features were observed simultaneously with the appearance of two peaks forbidden in the adopted sample geometry. The experimental results obtained are eventually discussed in comparison with recent experimental and theoretical works.

Polarized and depolarized room temperature light scattering spectra of normal alcohols from methanol to pentanol have been measured up to 80 cm−1 frequency shift. At low frequency shifts (smaller than 4 cm−1), resolutions as high as 0.04 cm−1 have been used. The possibility of using the same spectrometer for measuring both low frequency Brillouin structures and high frequency depolarized tails allows for the first time a precise determination of both lineshapes and relative integrated intensities between the various spectral components. The experimental results are presented and briefly discussed on the basis of the existing theories for depolarized scattering from molecular liquids.

An interpretation of the low frequency Raman scattering in all disordered systems including liquids is suggested in terms of phononlike excitations damped by anharmonicity and by structural relaxations. In principle, owing to the disorder‐induced breakdown of the k vector selection rule, all of these excitations are allowed to participate to the scattering process. An ad hoc simplified model is also proposed to calculate the low frequency Raman scattering, and it is found to reproduce at least qualitatively the main features of the depolarized spectrum in amorphous solid and liquid 10M KOH water solutions at different temperatures.

Depolarized Rayleigh spectra of water have been measured as a function of density along several isotherms in both liquid and supercritical phases. At all the thermodynamical states the spectral line shape can be fitted by a Lorentzian line superimposed to an exponential background. The behavior of the fitting parameters shows that at temperatures lower than ∼470 K the temperature is the most relevant parameter in determining the dynamics of the system, whereas above this temperature both temperature and density play a relevant role. Both the line shape and intensity of the spectra can be consistently interpreted in the framework of the first‐order dipole induced dipole approximation to the collision‐induced light scattering. The data show a clear evidence for cancellation effects.

We analysed, using micro-Raman spectroscopy, two decorations of a medieval manuscript containing the 'Canzoniere' and the 'Trionfi' of Francesco Petrarca; namely a drawing attributed to Botticelli and the illumination of the Incipit of the 'Trionfi'. All measurements were carried out at two excitation wavelengths (l632.8; l514.5 nm). The spectra of the drawing showed the presence of lazurite, Na8(Al6Si6O24)Sn, the coloured matter of lapis-lazuli, and of lead dioxide, coming from the oxidation of lead white or biacca, 2 PbCO3·Pb(OH)2. The illumination on a nearby page is a flower decoration, surely drawn by a different artist, in which we recognized the presence of cinnabar, HgS, lead tin yellow (type I), PbSnO4 and azurite, 2 CuCO3·Cu(OH)2, a blue pigment cheaper than lazurite. © 2000 Editions scientifiques et medicales Elsevier SAS

The newly built ultraviolet Raman–Brillouin spectrometer at the Universita di L'Aquila is described. We have used it to perform accurate ultraviolet and visible Brillouin spectra of glass-forming glycerol. Data with high contrast and high dynamic range in the unexplored region of wave vectors from 40 up to about 70 µm−1 have been obtained for the first time. The spectra are analysed in terms of generalized hydrodynamics with a frequency-dependent viscosity.

The dynamic structure factor, $S(Q,E)$, of neon has been studied by inelastic x-ray scattering and by molecular dynamic simulation in the momentum transfer region $Q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1--25{\mathrm{nm}}^{\ensuremath{-}1}$ at $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}295\mathrm{K}$ and $P\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3\mathrm{kbar}$. At this density, comparable to that of the liquid at ambient pressure, the shape of $S(Q,E)$ evolves from a Brillouin triplet towards a complex single line shape, which precurs the shape expected for single-particle behavior. The data, analyzed using the three mode model of the molecular hydrodynamics, show the absence of positive dispersion in the sound velocity and a minimum in the dispersion curve.

Low frequency translational spectra of 15 M NaOD heavy water solutions are analyzed in both liquid and amorphous phases. Confirming the results of previous findings in KOH water solutions, the analysis suggests that the spectra reflect in both phases the translational density of the states of the system. In agreement with inelastic neutron scattering experiments, these can be thought of as propagating quasi-phonon excitations. A polarization analysis of the spectra based on the results of a model recently developed for orientationally disordered crystals, allows a separation between acoustic-like and optic-like modes and clearly shows the presence of a low frequency relaxation process. The presence of this feature is also related to radiation coupling coefficients of the acoustic-like modes.