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Herewith, we present fast Fourier transforms of time resolved signals, obtained by use of the femtosecond transient transmission (TT) spectroscopy, for three tetrachlorides, CCl4, SiCl4, and GeCl4, and chloroform, CHCl3. Due to coherent excitation of molecules, the isotopic splitting of their spectral bands in the range of symmetric stretching vibration can be observed with high resolution not available in spontaneous Raman scattering. The intensity distribution in the isotopic fine structure pattern appears to differ for various studied molecules, which is explained by the role of intermolecular interactions and the local order of molecules in the liquids. In particular, in SiCl4, the vibrational band exhibits anomalous ratios of the peak amplitudes, which do not agree with the natural abundance of the isotopologues. Using the simple oscillatory model of the liquid and fitting theoretical curves to the experimental results, we have been able to find the intermolecular force constants for all three liquids and to formulate the conclusion that the anomalous spectral pattern in SiCl4 results from strong interactions between the closest Cl atoms belonging to adjacent molecules. Application of the windowed Fourier transform enables us to study the dynamics of intermolecular interactions. The strength of intermolecular interactions in CCl4, SiCl4, and GeCl4, found by the TT technique, is compared with the results obtained by means of the femtosecond optical Kerr effect spectroscopy. [ABSTRACT FROM AUTHOR]

We have studied the effect of transient vibrational inversion of population in trans-β-apo-8'-carotenal on the time-resolved femtosecond stimulated Raman scattering (TR-FSRS) signal. The experimental data are interpreted by applying a quantum mechanical approach, using the formalism of projection operators for constructing the theoretical model of TR-FSRS. Within this theoretical frame we explain the presence of transient Raman losses on the Stokes side of the TR-FSRS spectrum as the effect of vibrational inversion of population. In view of the obtained experimental and theoretical results, we conclude that the excited S2 electronic level of trans-β-apo-8'-carotenal relaxes towards the S0 ground state through a set of four vibrational sublevels of S1 state. [ABSTRACT FROM AUTHOR]

Herewith we present the results of our studies on the effect of confinement on the solvation of ethyl alcohol in aqueous solutions using Raman spectroscopy of the O-H stretching band. Based on Gaussian-Lorentzian deconvolution of the O-H band Raman spectra we investigate the local structures created between water-water, water-alcohol, and alcohol-alcohol molecules, which are directly related to the solubility of the liquids. Comparison of the responses in bulk solutions and in solutions confined in the pores of the gelatin gel shows that for high ethanol concentrations solubility significantly increases with decrease of the pore sizes. [ABSTRACT FROM AUTHOR]

We report on the investigation of a short-time collective dynamics of water confined in the pores of the gelatin gel, using the femtosecond optical Kerr effect spectroscopy. The ultrafast responses of water molecules obtained in bulk liquid and in three concentrations of gelatin gels are explained theoretically, both in a long time and in a short time regime, taking into account all molecular motions. We prove that the contribution of molecules involved in tetrahedral, strongly H-bonded structures stabilizing the gel network increases with the gel concentration. On the other hand the long-time relaxation of water molecules is significantly slowed down in the gel pores. [ABSTRACT FROM AUTHOR]

Presents a theoretical model of ultrafast dynamics for the optical Kerr effect in molecular liquids. Interaction of the quasicrystalline structures with a femtosecond laser pulse; Role of local phonons for the subpicosecond polarizability of molecular liquids; Account on the lifetime of dynamic structures at room temperature.

The dynamics of intramolecular and intermolecular vibrations in liquid tetrachloroethylene are studied for the first time by use of femtosecond time-resolved techniques, such as transient transmission spectroscopy and optical Kerr effect spectroscopy. Fourier transforms of time signals are compared with spontaneous Raman spectra for both isotropic and anisotropic components. The isotopic effect resulting from natural abundance of chlorine isotopes manifests itself as splitting of the isotropic spectra of intramolecular symmetric vibrations. Application of windowed Fourier transform enables us to study the dynamics of both spectral responses in real time and to analyze the role of intermolecular interactions on the coherence in the system. In order to describe the dynamics of molecules in a liquid and to explain the experimental results, we use a simple theoretical model taking into account intermolecular interactions, which allowed us to find vibrational and rotational life times. [ABSTRACT FROM AUTHOR]

In the present paper, we have studied the temperature dependence of translational diffusion and solvation dynamics of a dissolved dipolar dye in the nonionic acetamide-urea deep eutectic solvent (DES), to characterize the viscosity coupling of the measured relaxation times and verify the dynamical heterogeneity aspect of this medium. Three different time-resolved experimental techniques have been employed for this purpose: fluorescence correlation spectroscopy, transient absorption (TA) spectroscopy, and optical Kerr effect (OKE) spectroscopy. The first method provides the proof that the translational diffusion time of a solute in acetamide-urea DES [ f CH 3 CONH 2 + (1 - f )CO(NH 2 ) 2 , f = 0.6] exhibits a fractional viscosity dependence, with exponent 0.758, which, when compared with the viscosity-diffusion relationship for the same solute in common molecular solvents, suggests moderate deviation from the Stokes-Einstein relation. Stokes shift dynamics of a solvatochromic dye, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4 H -pyran in this DES, followed via femtosecond TA measurements, have been found to be triexponential in nature and dominated by a ∼100 fs component. The other two components, which contribute to a total dynamic Stokes shift magnitude of ∼2500 cm -1 , are characterized by time constants in the ∼5 and ∼50 ps regimes. Subsequent comparison with the femtosecond OKE measurements suggests that the relatively slower picosecond solvation components originate from the rapid reorientation of the solvent molecules, while the subpicosecond solvation response arises from the participation of the collective low-frequency solvent modes (such as intermolecular vibrations and librations). We find that the rotational diffusion lifetimes also exhibit fractional power dependence on medium viscosity and thus deviate from the Stokes-Einstein-Debye pprediction. All of these results therefore suggest that the nonionic acetamide-urea DES is a moderately heterogeneous medium.

We report our study on the ultrafast dynamics of intermolecular interactions in liquid CCl4. A transient transmission time domain signal, obtained in the 40 ps delay range, exhibits beating at the difference frequency of the totally symmetric stretching vibrations of the tetrachloride isotopologues. We show that the spectra obtained as the windowed Fourier transform of different parts of the time domain signal in the range of this totally symmetric vibration, split due to the isotope effect, carry the information about the dynamics of the coherently excited, coupled molecules. We use a simple theoretical model in order to prove that the intermolecular interaction influences the relative amplitudes of the isotopologue peaks in the spectrum. Moreover, we demonstrate that the pump induced coherence in the system leads to additional strengthening of the interaction, which can be observed in the spectra obtained from the experimental time domain signal.

Assigning the vibrational modes of molecules in the electronic excited state is often a difficult task. Here we show that combining two nonlinear spectroscopic techniques, transient 2D exchange infrared spectroscopy (T2D-IR-EXSY) and femtosecond stimulated Raman spectroscopy (FSRS), the contribution of the C═C and C═O modes in the excited-state vibrational spectra of trans-β-apo-8'-carotenal can be unambiguously identified. The experimental results reported in this work confirm a previously proposed assignment based on quantum-chemical calculations and further strengthen the role of an excited state with charge-transfer character in the relaxation pathway of carbonyl carotenoids. On a more general ground, our results highlight the potentiality of nonlinear spectroscopic methods based on the combined use of visible and infrared pulses to correlate structural and electronic changes in photoexcited molecules.

An extended cavity Ti:Sapphire oscillator exhibits stable operation for positively chirped pulses, while in the negative chirp regime multiple pulses are present in the cavity. At the border of these regimes automodulations, being an effect of the interplay between population inversion, laser medium polarization and the laser pulse field, appear. Two particular instabilities: period doubling and chaotic behavior of the pulse train envelope are observed. Complex temporal evolution of the pulse spectrum within the modulation period is investigated.

The evolution of water structure during the gelation process is examined in aqueous solution of agarose using Raman spectroscopy of the O-H stretching band. The measurements have been performed at room temperature for different concentrations of agarose, which yields different dimensions of nanopores in the network of the created gel. Our results show that water confined in the gel pores exhibits evident changes in the local order of molecules in comparison with bulk water and water in the sol state. During the sol-gel transition the number of molecules that participate in the regular tetrahedral H-bond structure increases, and the effect is stronger for higher concentration of the biopolymer., ((c) 2004 American Institute of Physics.)

The results of fluorescence quenching measurements, obtained for a dye-substituted aqueous gelatin solution during the sol-gel transition, are presented. Simultaneous optical polarization rotation and fluorescence studies allow us to find the dependence of the fluorescence yield on the amount of helix created in the medium. The exact gel point has been found as the point of inflection on the fluorescence yield versus the helix amount plot. The second-order character of the sol-gel transition is shown, which is in agreement with the theoretical predictions obtained by use of the percolation theory.

The parametric excitation of the low-frequency overtone in GaSe crystal by a biharmonic optical field is shown to lead to bistability of both the crystal refractive index and the optical field generated in the four-wave-mixing process. The effect appears to be much stronger in layered crystals than in crystals of higher symmetry.

Neurological examination including EEG, ENG and measurement of nerve motor conduction velocity were performed in 41 male workers, exposed to enolofos. 43% of the population examined developed subjective neurological symptoms 34%--discrete lesions of CNS and in 31% polineuropathy was observed. Motor nerve conduction velocity was decreased in 10 workers (24%) in peroneus nerves and in 1 worker in ulnaris nerve. Comparison of EEG and ENG with the control group was not statistically significant.

Cyclophosphamide (4000 mg intravenously, in daily doses of 400 mg) in combination with moderate dose of prednisone (1075 mg during 30 days) was given to 39 patients with the chronically progressing form of multiple sclerosis. The results of this treatment were evaluated immediately after the treatment and one and two years later, using a numerical scale of neurological examination in the scales of motor efficiency A. I. (ambulation index) and the DDS (disability status scale of Kurtzke). In the first year after this treatment stabilization of the disease (60% of cases) or even clinical improvement (10-20%) were noted. However, in the second year after the treatment an evident progression of symptoms occurred in 50-60% of cases. In view of moderately positive results of this treatment it is necessary to carry out observations extended over many years, to repeat cyclophosphamide cycles, and to compare the results with those after other immunosuppressants.

The aim of the reported study was an assessment of the effectiveness of high doses of methylprednisolone in the treatment of active exacerbation and its effect on the natural course of multiple sclerosis. The study was carried out on 24 patients with clinically certain disease, who were divided, according to the treatment given to them, into two subgroups: treated with methylprednisolone and treated with prednisone. The treatment was conducted by the double blind method. The statistical analysis of the results obtained in this material showed that in patients with acute and severe exacerbation of the disease methylprednisolone administration in high doses caused a rapid regression of paralysis and paresis and improved motor efficiency. However, an evaluation of the results after a year from treatment termination showed in both subgroups a progression of clinical changes and increased motor deficiency. This suggests that treatment with corticosteroids has no significant effect on the course of multiple sclerosis.