Depolarized Rayleigh Scattering Research Articles

Complex Dynamical Aspects of Organic Electrolyte Solutions

Molecular dynamics of acetone-alkali metal halide (LiBr, LiI) solutions were investigated using depolarized Rayleigh scattering (DRS) and low-frequency Raman spectroscopy in the frequency range from ~0.5 to 200 cm(-1) (~20 GHz to 6 THz). These experiments probe fast dynamical fluctuations of the polarizability anisotropy at picosecond and sub-picosecond time scales that are mainly driven by acetone orientational dynamics. Two distinct contributions were revealed: a fast process (units of picosecond, ps) related to the essentially unperturbed bulk solvent and a slow one (tens of ps) assigned to acetone molecules forming Li(+) solvation shells, decelerated by the motional constraint imposed by the cation. The increase of LiBr and LiI concentration significantly slows down the overall solvent relaxation as a consequence of the increased fraction of acetone molecules involved in the ion solvation shells. The global retardation is larger in LiI than LiBr solutions consistently with viscosity trends. This is explained in terms of ion association (at least ion pairing) more favorably promoted by Br(-) than I(-), with reduced Li(+)-acetone interactions in LiBr than LiI solutions. Anion-induced modulation of the Li(+)···O═C contacts, largely responsible for electrostriction phenomena, also affects the reduced THz-Raman spectral density, ascribed to ultrafast librational motions of acetone molecules. Overall, these findings enlighten the interplay between ion-dipole and ion-ion interactions on the fast solvation dynamics in electrolyte solutions of a typical polar aprotic solvent.

Dielectric Behaviors of Typical Benzene Monosubstitutes, Bromobenzene and Benzonitrile

The dielectric behaviors of typical benzene monosubstitutes, bromobenzene (Br-Bz) and benzonitrile (NC-Bz), were investigated up to 3 THz in the pure liquid state over a temperature range from 10 to 60 °C to understand differences in molecular motions of these simple, planar molecules bearing rather different electric dipole moments: 1.72 and 4.48 D for Br-Bz and NC-Bz in gaseous state, respectively. Temperature dependence of spin-lattice relaxation time (T(1)) for (13)C NMR and viscosities for these liquids were also determined to obtain information for molecular motions. Moreover, depolarized Rayleigh scattering (DRS) experiments were carried out for both liquids at 20 °C to determine frequency dependencies of optical susceptibilities up to 8 THz directly relating to rotational motions of their molecular planes. Most Br-Bz molecules rotate freely over a temperature range examined, showing a Kirkwood correlation factor close to g(K) ∼ 1.0 at dielectric Debye-type relaxation times (ca. 18 ps at 20 °C) essentially identical to microscopic (dielectric) relaxation times evaluated from T(1)(13)C NMR data. A small amount of Br-Bz molecules forms dimeric intermolecular associations in an antiparallel configuration of dipole moments. On the other hand, NC-Bz molecules form stable dimers in the antiparallel dipole configuration at a population much higher than that of Br-Bz because of a markedly greater dipole moment than that of Br-Bz. A major dielectric relaxation mechanism for NC-Bz found at ca. 70 ps at 20 °C results from the dissociation process of dimers with a lifetime longer than a rotational relaxation time, observable as a minor dielectric relaxation mechanism at ca. 12 ps at 20 °C, of individual monomeric NC-Bz molecules without the formation of dimers. The formation of stable dimers in an antiparallel configuration is responsible for the observed small g(K) values, ca. 0.5, and disagreement between major (or minor) dielectric relaxation times and microscopic dielectric relaxation times over the entire temperature range examined.

Hydrogen bond dynamics and water structure in glucose-water solutions by depolarized Rayleigh scattering and low-frequency Raman spectroscopy

The effect of glucose on the relaxation process of water at picosecond time scales has been investigated by depolarized Rayleigh scattering (DRS) experiments. The process is assigned to the fast hydrogen bonding dynamics of the water network. In DRS spectra this contribution can be safely separated from the slower relaxation process due to the sugar. The detected relaxation time is studied at different glucose concentrations and modeled considering bulk and hydrating water contributions. As a result, it is found that in diluted conditions the hydrogen bond lifetime of proximal water molecules becomes about three times slower than that of the bulk. The effect of the sugar on the hydrogen bond water structure is investigated by analyzing the low-frequency Raman (LFR) spectrum sensitive to intermolecular modes. The addition of glucose strongly reduces the intensity of the band at 170 cm(-1) assigned to a collective stretching mode of water molecules arranged in cooperative tetrahedral domains. These findings indicate that proximal water molecules partially lose the tetrahedral ordering typical of the bulk leading to the formation of high density environments around the sugar. Thus the glucose imposes a new local order among water molecules localized in its hydration shell in which the hydrogen bond breaking dynamics is sensitively retarded. This work provides new experimental evidences that support recent molecular dynamics simulation and thermodynamics results.

Rotational Friction Kernel in Water from the Femtosecond Time-Resolved Optical Kerr Effect of Acetonitrile/Water Mixtures

Depolarized Rayleigh scattering (DRS) of acetonitrile/water mixtures is examined with the time-resolved, heterodyne-detected optical Kerr effect (OHD-OKE). For neat water, the rise of electronic response gives a symmetricapparatus function and an asymmetric correction is constructed with the help of high-frequency Raman data. For the mixtures at 21 °C, depolarized Raman spectra up to 1600 cm - 1 are obtained with high signal/noise ratio. The DRS spectra for acetonitrile mole fraction 0.05 ≤ x A C N ≤ 1 are decomposed into the spectra of water and of neat acetonitrile and a composite spectrum with associated weight functions. The spectral density at infinite dilution in water is obtained by extrapolation and transformed into the second-rank orientational correlation function of single acetonitrile solutes. The Einstein frequency of 31.11 cm - 1 is higher than the value of 27.11 cm - 1 for the potential-free stochastic rotor and an oscillation is observed in the corresponding velocity correlation function, both indicating librational motion in a solvent cage. The rotational correlation time τ 2 = 1.49 + 0.015 ps may be used to rescale τ 2 values from 1 4 N nuclear quadrupole relaxation in water; the comparison provides an improved value 4.54 ′ 0.03 MHz for the coupling constant. The correlation function is inverted to give the kernel for rotational friction. The latter consists of a fast biexponential decay with a 33-fs correlation time followed by exponential decay with a 0.779-ps time constant. An oscillatory residue around 0.3 ps indicates coupling between acetonitrile libration and the water frictional modes.

2B12 Depolarized Rayleigh 散乱によるネマチック液晶の分子分極率異方性の測定

2B12 Depolarized Rayleigh 散乱によるネマチック液晶の分子分極率異方性の測定

Perturbation approach to depolarized Rayleigh band shape theory corrected for collision-induced coherence: applications to hydrogen and deuterium

Depolarized Rayleigh Scattering (DPR) relaxation matrix is obtained by the second-order Fano-Mori perturbation theory with allowance for the collision-induced polarization transfer. For room-temperature hydrogen and deuterium, the DPR relaxation matrix elements are expressed via kinetic coefficients obtained previously (A.P. Kouzov and V.A. Krasheninnikov, Chem. Phys. 126 (1988) 301) by analyzing the experimental rotational Raman halfwidths. With the polarization transfer within each ( ortho- or para-) species accounted for, the calculated DPR relaxation rates agree well with experiment thus showing applicability of the second-order treatment to the studied systems. For the first time, the spectrum corrections due to collision-induced correlation between optical transitions in dissimilar molecules are derived. Such correlation does not change the integral DPR intensity, but affects the shape leading to nonadditive DPR responses from ortho- and para-molecules. Although this ortho- para correlation does not strongly increase the DPR relaxation rates in normal molecular hydrogen (1.5% in n-H 2 and 4% in n-D 2), the effect may be enhanced in binary gas mixtures of heavier rotators.

Dicarbocyanine dyes in methanol solution probed by depolarized Rayleigh and hyper-Rayleigh light scattering

The hyper-Rayleigh scattering (HRS) intensity of two symmetric carbocyanine dyes (1122 DEDC and 1144 DEDC, full names given in the text) in methanol is measured as a function of dye concentration. These dye molecules at equilibrium show a negligible permanent dipole moment. The low concentration data showing that the HRS intensity is proportional to the dye concentration are used to determine the first hyperpolarizability for each of these dyes. However, above a concentration ρb=0.1×10−3 M, the HRS intensity shows an anomalous concentration dependence. Above ρb, the HRS intensity shows a saturation behavior and it even decreases with increasing concentration at high dye concentration. The depolarization ratio of the HRS intensity is also measured as a function of dye concentration. At lowest concentration, the depolarization ratio is 0.18. As the dye concentration increases, the depolarization ratio also rapidly increases but the increase quickly saturates as the concentration exceeds ρb. The concentration dependence of the HRS intensity and depolarization ratio are interpreted as due to formation of molecular aggregates. The depolarized Rayleigh scattering (DRS) intensity is also measured as a function of dye concentration. The result of DRS corroborates well with that found in HRS.

Determination of Chain Conformation of Stiff Polymers by Depolarized Rayleigh Scattering in Solution

The chain conformation of a series of polydisperse polyesters and poly(p-phenylenes) has been investigated by means of depolarized Rayleigh scattering in solution. By considering polydisperse worm-...

Solvent and polymer dynamics in concentrated polystyrene/toluene solutions

Depolarized Rayleigh scattering (DRS) and dielectric spectroscopy (DS) are employed to study the solvent and polymer dynamics in the polystyrene (PS)/toluene system and for PS concentration up to 0.6 g/ml. The DRS measurements were made in the temperature range from 255 to 373 K with different interferometers making possible the separation of the ‘‘fast’’ solvent (in the ps time scale) from the ‘‘slow’’ polymer dynamics (in the ns time scale). The DS measurements were made in the temperature range from 128 to 310 K and two processes could also be observed. With DRS and DS we investigate the very different mobilities in the PS/toluene solutions over a frequency range of ∼10 decades. The prominent features of the experimental data are (i) the existence of two primary (α−) relaxations in the macroscopically homogeneous solutions which have been analyzed using both techniques and (ii) that these relaxations reflect the polymer and solvent dynamics and display the usual Vogel–Fulcher–Tammann behavior, however, with a broad distribution of relaxation times, especially at low temperatures. The existence of two time scales in the solutions is discussed in terms of concentration heterogeneities composed of PS-rich and toluene-rich domains, large enough to exhibit two glass transitions. As a result of the strong temperature dependence for the fast solvent reorientation times the rate of change of solvent friction with polymer concentration becomes temperature dependent at low temperatures.

Segmental and chain dynamics in a diblock copolymer melt near the microphase separation transition

The dynamics of segmental and chain orientation in poly(styrene- b-isoprene) (P(S- b-I)) block copolymer with PI fraction f PI = 0.61, degree of polymerization N = 70 and χN ⋍ 9 at 25°C (χ is the interaction parameter) were investigated by depolarized Rayleigh scattering (DRS) and dielectric spectroscopy (d.s.) over a broad temperature range (240–370 K) in the disordered phase. Two distinct primary relaxation processes with vastly different timescales were associated with segmental orientation within PS- and PI-rich regions selectively probed by DRS and d.s. techniques. The width of the distribution relaxation function for the slow segmental process was found to increase with decreasing temperature, whereas the freezing of the slow segmental fluctuations was observed for the first time within the time window of photon correlation spectroscopy. Compared with an equivalent PI homopolymer chain, the first normal mode describing the end-to-end fluctuation of the copolymer chain displayed slower time τ 1 but similar amplitude δε N f PI . The new experimental results were discussed in terms of the fluctuation picture of block copolymers in the disordered melt, the chain conformation and the friction coefficient ratio of the foreign blocks.

Dynamic light scattering from a polymer/additive system

Photon correlation spectroscopy (PCS), dielectric and mechanical relaxation techniques are employed to examine the effects of the additive di-2-ethylhexylphthalate (DOP) on the relaxation processes of bulk poly(cyclohexylmethacrylate) (PCHMA). The primary (α-) relaxation is shifted to lower temperatures, and the sub- T g or β-relaxation is enhanced with increasing DOP content, whereas the γ-relaxation (associated with specific motion of the cyclohexyl ring) is insensitive to the additive content. Depolarized Rayleigh scattering (DRS) is utilized to investigate the reorientation of DOP in the presence of the high molecular-weight polymer matrix. For the additive concentration used (0–20%), DRS reveals a strong slow-down of the reorientational motion of DOP at high temperatures, which gives rise to a broad distribution of relaxation times covering about 8 decades of time/frequency. The present study shows, for the first time, that a much broader distribution of reorientational relaxation times, as compared with density relaxation times, can be observed in a polymer/additive system.

A comparison of models for depolarized light scattering in supercritical CO2

Depolarized Rayleigh scattering (DRS) in supercritical CO2 is studied using molecular dynamics computer simulation. Results are presented for three thermodynamic states at approximately 313 K and at the following densities; ρ/ρc=1.38, 1.95, and 2.35, where ρc=0.468 g/cm3 is the critical density. We study the effects of intermolecular potential and interaction-induced polarizability models on the DRS spectra. Results for three different atom–atom intermolecular potentials are compared: Two potentials with Lennard-Jones and Coulomb terms, one developed by Murthy, Singer, and McDonald (MSM) and the other by Steele and Posch, as well as a third potential with MSM Lennard-Jones parameters, but without Coulombic interactions. The interaction-induced polarizability is calculated using center–center and site–site dipole–induced dipole (DID) interaction models. First order perturbation theory results are obtained for both models. The exact solution of the center–center DID model is also obtained. We find that both polarizability delocalization and higher-order DID interactions have a significant impact on the DRS intensity, but a more modest one on the related time-dependent properties. The results for the three intermolecular potentials differ significantly, with those for the MSM potential being in closest agreement with the experimental data. The collision-induced contribution to the DRS spectrum is found to decrease with increasing density and to exhibit cancellation effects due to contributions from 3 and 4 molecule correlations.

Effects of intermolecular interactions on depolarized Rayleigh scattering intensities of fluids of linear molecules

We report the results of a study of interaction-induced (I-I) effects on the depolarized Rayleigh scattering (DRS) intensity of fluids of linear molecules. Monte Carlo and molecular dynamics computer simulation, as well as analytical theory, are used to calculate DRS intensities of model fluids designed to represent N2, CO2, and O2 at a set of densities and temperatures. The I-I, or ‘collision-induced’, polarizability is evaluated using the first order dipole-induced dipole model. The contributions to the intensity from intermolecular pair correlations, cross-correlations between molecular and I-I polarizability, and collision-induced polarizability autocorrelation, are studied. With the aid of the analytical theory, the computer simulation results are analysed in terms of the density dependence of the correction factors F cc and F mc, measuring the contributions of triplet and higher intermolecular correlations to collision-induced and cross terms in the intensity. We find that molecular shape, polarizability, and temperature of the fluid can have important effects on the density dependence of the DRS intensity. We also find that the polarizability anisotropy contribution to the I-I polarizability substantially affects the DRS intensity at high densities.

Correction of Collision-Induced Polarizabilities to the Depolarized Rayleigh Scattering by Dilute Solutions of Oligomers and Polymers

Abstract It is shown that the correction of collision-induced polarizabilities to the depolarized Rayleigh scattering intensity may be made using a usual light-scattering photometer with a mercury lamp as a light source if its spectral distribution is narrow.

Experimental and molecular dynamics study of depolarized Rayleigh scattering by O2

Collision-induced effects on depolarized Rayleigh scattering (DRS) in gaseous oxygen at 300 K in the pressure range from 10 to 3000 bar have been studied experimentally. DRS spectra for four thermodynamic states at this temperature and in the pressure range from 130 to 3000 bar have also been obtained from molecular dynamics (MD) simulation. Molecular trajectories were calculated using the Lennard-Jones atom–atom potential and the system polarizability was modeled using the first order dipole–induced dipole approximation. The frequency dependence of DRS band shapes is well reproduced by the MD results, which predict that the orientational contribution dominates the overall band shape. The agreement between experimental and calculated second, fourth, and sixth spectral moments is very good. The observed density dependence of the spectral moments is analyzed in terms of contributions from the collision-induced (CI) polarizability component and orientational pair correlations. The second spectral moment, M2, is found to decrease with increasing density at low densities and to increase at higher densities. The MD results indicate that the initial decrease in M2 is due primarily to slow relaxation of the CI polarizability at low densities. The increase in M2 at higher densities is found to be mainly due to the contribution from orientational-CI cross correlations. MD results as well as analytical calculations, carried out for the low density limit, predict that the CI contribution to the total DRS intensity remains relatively small (≤4%) throughout the entire density range. The observed density dependence of the intensity is not consistent with these calculations. Possible sources of this disagreement are discussed.

Separation of temperature and density effects on collision-induced Rayleigh and Raman line shapes of liquid carbon disulfide

Quantitative results for the separate temperature and density effects on collision-induced scattering (CIS) line shapes for the dense molecular fluid CS2 are presented for the temperature range T=293–353 K and density range ρ=1.25–1.48 g cm−3. The depolarized Rayleigh scattering (DRS) and ν1, ν2, and ν3 mode Raman scattering line shapes are specifically investigated. The three distinctive CIS line shape regions observed, corresponding to low, intermediate, and high frequency line shape ranges, are interpreted qualitatively in terms of available theoretical models. The results generally support the multipole–induced-dipole interaction mechanism for all CIS line shapes at all frequencies, and the dominance of translational over orientational dependence of the induced dipole moment at intermediate and high frequencies of CIS line shape.

Depolarized Rayleigh Scattering from CO2: An Experimental and Molecular Dynamics Investigation

AbstractA direct comparison of experimental depolarized Rayleigh spectra of CO2 with those obtained by molecular dynamics (MD) simulations at two different statepoints are reported. For the MD simulations a three Lennard‐Jones centres and central point quadrupole moment (3LJC + Q) interaction model has been used. Total depolarized spectra as well as their constituents (a) orientational, (b) collision induced, and (c) cross spectra were calculated for two polarizability models: In the first centre‐centre (C‐C) model the molecular polarizability is placed in the centre of the molecules whereas in the second site‐site (S‐S) model two partial polarizabilities are placed on the O atom sites. At the lower density the spectra resulting from both polarizability models compare well with the experimental spectrum. At the high density both model spectra noticeably deviate from the experimental one: the C‐C model spectrum giving the better description. This result is in contradiction to a previous investigation based on a two Lennard‐Jones centres potential. Thus any assessment of the relative merits of the two polarizability models seem to be premature at this stage since the role played by the interaction potential is not fully understood.

ChemInform Abstract: STUDIES OF SILOXANE OLIGOMERS BY DEPOLARIZED RAYLEIGH SCATTERING

Chemischer InformationsdienstVolume 15, Issue 46 Physical Organic Chemistry ChemInform Abstract: STUDIES OF SILOXANE OLIGOMERS BY DEPOLARIZED RAYLEIGH SCATTERING G. FYTAS, G. FYTASSearch for more papers by this authorC. H. WANG, C. H. WANGSearch for more papers by this author G. FYTAS, G. FYTASSearch for more papers by this authorC. H. WANG, C. H. WANGSearch for more papers by this author First published: November 13, 1984 https://doi.org/10.1002/chin.198446046Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume15, Issue46November 13, 1984 RelatedInformation

ChemInform Abstract: DEPOLARIZED RAYLEIGH SCATTERING FROM LIQUID BINARY MIXTURES

Chemischer InformationsdienstVolume 13, Issue 10 Physical Organic Chemistry ChemInform Abstract: DEPOLARIZED RAYLEIGH SCATTERING FROM LIQUID BINARY MIXTURES R. VILHJALMSSON, R. VILHJALMSSONSearch for more papers by this author R. VILHJALMSSON, R. VILHJALMSSONSearch for more papers by this author First published: March 9, 1982 https://doi.org/10.1002/chin.198210042AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue10March 9, 1982 RelatedInformation

Static and Dynamic Depolarized Rayleigh Scattering of Cyano Biphenyl Series in Dilute Solutions and Intrinsic Molecular Even-Odd Effect in Liquid Crystals

Abstract We report here a detailed description of our experimental work about both static and dynamic investigations of depolarized Rayleigh scattering and Kerr effect in diluted solutions of the cyanobiphenyl series, and show how a carefully performed conformational analysis can lead to a possible interpretation of the intrinsic molecular even-odd effect experimentally evidenced.