Are vibrational relaxation times really constant? II. The vibrational relaxation of C2H2

Vibrational relaxation times of pure acetylene in the gas phase were measured behind incident shock waves in the temperature range 613–1184 K using a laser-schlieren technique. Overall, the results are in excellent agreement with those of acoustic and laser excitations. However, we find a marked intrinsic time dependence of the phenomenological time, which varies by factors of two to three over a wide dynamic time scale of at least six natural lifetimes. In other words, the Bethe—Teller law fails. This is confirmed by numerical solution of the master equation for a wide choice of intermode collisional coupling parameters. The density of states involved in the energy transfer process determines whether the relaxation time increases or decreases with time, and the effect is amplified by the importance of intermolecular VV processes relative to intramolecular processes.     

The lighter side of darwinism? Photoselection of the species: Applications of luminescence anisotropy measurements to the study of polymer relaxation

The application of luminescence anisotropy techniques to the study of polymer systems is discussed. Investigations of polymer relaxation both in fluid solutions and the solid state are addressed. Particular attention has been paid to considerations of reliable means of information retrieval from experimental time-resolved anisotropy data.     

Enthalpic relaxation of silica–polyvinyl acetate nanocomposites

Although the effects of filler nanoparticles size and surface treatment on the glass transition temperature of the matrix phase have received well-deserved attention, nanofiller effects on other physical parameters associated with the glass transition have received less interest. To better understand how the incorporation of nanofillers affects the enthalpic relaxations associated with the glass transition, differential scanning calorimeter measurements were carried out on silica–polyvinyl acetate nanocomposites with respect to filler content, annealing temperature, and annealing period. As expected, longer annealing periods below the glass transition temperature resulted in an increase of the subsequent enthalpic relaxations. However, the presence of filler substantially reduces the enthalpic relaxation relative to that of the neat polymer at longer annealing periods only. The underlying enthalpic relaxations and the effects suppressed by the fillers are specific to the annealing temperature. These results suggest a significant alteration in the physical state of the matrix because of the presence of the filler particles. However, this does not imply the existence of a glassy layer or layers with a glass transition gradient near the filler surface. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2733–2740, 2008     

The Division of Analytical Chemistry of The Federation of European Chemical Societies

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Do theories of the glass transition, in which the structural relaxation time does not define the dispersion of the structural relaxation, need revision?

Upon decreasing temperature or increasing pressure, a noncrystallizing liquid will vitrify; that is, the structural relaxation time, taualpha, becomes so long that the system cannot attain an equilibrium configuration in the available time. Theories, including the well-known free volume and configurational entropy models, explain the glass transition by invoking a single quantity that governs the structural relaxation time. The dispersion of the structural relaxation (i.e., the structural relaxation function) is either not addressed or is derived as a parallel consequence (or afterthought) and thus is independent of taualpha. In these models the time dependence of the relaxation bears no fundamental relationship to the value of taualpha or other dynamic properties. Such approaches appear to be incompatible with a general experimental fact recently discovered in glass-formers: for a given material at a fixed value of taualpha, the dispersion is constant, independent of thermodynamic conditions (T and P); that is, the shape of the alpha-relaxation function depends only on the relaxation time. If derived independently of taualpha, it is an unlikely result that the dispersion of the structural relaxation would be uniquely defined by taualpha.     

The Synthesis of Polyfluoroalkylbiphenyl

Polyfluoroalkylated biphenyl was obtained from reaction of benzene with R_FI/Na_2S_2O_4 using cetyltrimethylammonium bromide (CTAB) as PTC followed by dehydrogenation with DDQ in 38-43% yield.     

The Synthesis of Glycoglycerolipids

A convenient synthetic route was developed for the synthesis of the novel glycolipids: 1,2-di-O-acyl-3-O-(2‘-acylamide-2‘-denxy-ct-D-glucopyranosyl)-sn-glycerols. 10 new compounds of glycolipids with different acyl groups were obtained.     

The Enhancement of Fluorescence of The Squaraine Dye LB Films by Overcoating of Glycolipids

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Dielectric relaxation study of formamide–propylene glycol using time domain reflectometry

Using picoseconds time domain reflectometry, dielectric relaxation studies have been carried out for formamide (FMD)–propylene glycol (PLG) mixtures over the frequency range from 10?MHz to 20?GHz at various temperatures. The dielectric parameters, i.e. static dielectric constant (ε ₀) and relaxation time (τ), have been obtained by Fourier transform and least squares fit methods. The excess dielectric properties and Kirkwood correlation factor of the mixtures have also been determined. The Kirkwood angular correlation factor is greater than one (g ^eff?>?1) in FMD-rich region and less than one (g ^eff?<?1) in PLG-rich region, which indicates that in the mixture the dipole pairs have been formed in such a way that their orientation is parallel in FMD-rich region and antiparallel in the PLG-rich region.     

Resonance of relaxation time in the temperature modulated Schlögl model

We show the possibility to accelerate-in a resonant way-a nonlinear chemical reaction by imposing a small temperature modulation. This classical resonance, which happens for particular modulation frequencies, is illustrated on the athermic cubic Schlogl model, which allows us to get analytical expressions for both the reaction relaxation time and the frequency-resonant delay.     

Dielectric relaxation of Tripropylene glycol–water mixture using time domain reflectometry

The complex permittivity spectra of tripropylene glycol and water solutions have been obtained by time domain reflectometry (TDR) technique in the frequency range from 10 MHz to 30 GHz and the temperature range 20°C–05°C. The dielectric relaxation parameters such as static dielectric constant and relaxation time were obtained by using the non-linear least square fit method. The intermolecular hydrogen bonding of tripropylene glycol–water has been discussed using the Kirkwood correlation factor and thermodynamic parameters. The activation energy decreases with increase in water content in the mixture as expected in the Arrhenius behaviour. The dielectric constant for mixtures has been fitted to the Bruggeman mixture formula in the non-linear case.     

Dielectric relaxation study of aqueous α-amylase using time domain reflectometry technique

Time domain reflectometry technique has been used to study the complex permittivity spectra of aqueous α-amylase solution at different pH. Static dielectric constant and relaxation time were obtained from the complex permittivity spectra using nonlinear least square fit method. The dielectric relaxation parameter increases with an increase in molar concentration of α-amylase in water due to the formation of hydrogen bonding. The hydration numbers were also determined from the static dielectric constant.     

Acceleration of carbon-13 spin-lattice relaxation times in amino acids by electrolytes

A series of amino acids and carboxylic acids were determined by C NMR spectroscopy. 13 The results showed that addition of 3M MgCl2 led to the C NMR integral area of samples being 13 well proportional to number of carbon atoms that produce the particular signal with reliability over 95%. Measurements of C spin-lattice relaxation times (T1’s) are reported for a number of amino 13 acids. T1’s of all the carbons in amino acids generally tend to decrease with the increase of the c…     

The Chemistry of Hainanensine Derivatives

Hainanensine(1) and its analog 6 were obtained through intramolecular regiospecific cycliza-tion. Reduction of 6 under different conditions gave 7～12. The stereochemistry was established bychemical correlation, spectral analysis and X-ray diffraction.     

The Preparation of β-Hydroxysulfoxides

. Oxidation of β-hydroxy thioethers with MnO₂-aqu. 35%/HCl in methanol gives β-hydroxy sulfoxides in high yields.     

The First Hyperpolarizabilities of Merocarbocyanines

IntroductionPhotorefractive(PR)materialscanbeusedinvariousaPplications,suchasimageprocessing,highdensityopticaldatastorage,opticalinterconnects,andopticalphaseconjugations.However,mostofthereportedPRcomPositesaredopingsystems.ThephaseseparationofcomPonentshaslimitedtheirinvestigation.Toovercomethisdisadvantage,theuseofthemulti-propertieschromophoresmaybeoneoftheeffectiveapproaches.Merocyaninesarenotonlygoodphotoconductivedyes,butalsowidelyusedaschromophoresinnonlinearopticalLBfilmsduetothe…     

Density and temperature dependence of the relaxation of the 1Δg state of highly compressed O2 fluid

The electronic relaxation of O₂ is investigated by an absorption excitation and fluorescence detection technique. The relaxation rate constant of O₂(¹Δ_g) is measured in the density range from 10²¹ to 3 × 10²² cm⁻³ at temperatures between 90 and 295 K. The experimental results are compared with theoretical models based on the pair distribution functions of the fluid. The effects of intermolecular potentials with hard or soft cores are discussed.     

Nuclear magnetic relaxation of protons in “polyantimonic acid–phosphate” composites

The results of studying MeH₂PO₄ (Me = K, Na)/Sb₂O₅ · 2.7H₂O composites using the pulsed NMR spectroscopy technique at the temperatures of 20–140°C are presented. The contribution of interfaces, a subsystem formed due to interaction between the components of the composite, is identified in the signals of transverse magnetization decay. Protons near the interfaces are in two states, mobile and bound, and the fraction of mobile protons increases with the temperature, as all protons prove to be in the mobile state at the temperatures above 80°C. The composition of the interface is determined by the ion exchange reaction between components and is close to phosphoric acid. The obtained results explain the observed increase in conductivity of composites as compared to pure components.