Advances in Molecular Relaxation and Interaction Processes最新文献

The methanolic and methanolic aqueous or aqueous solutions of the first three representatives of the homologeous series of 3,3′-diethyl-2,2′ benzthiacyanines exhibiting an increasing dimerisation with an increasing amount of water in the solvent have been investigated by spontaneous Raman scattering and CARS with different optimum excitation frequencies. Within the accuracy of our experiments (⁺−10 cm⁻¹) there are no differences between the measured Raman wave numbers of the chromophoric system of monomers and dimers.

Infrared and Raman spectra of 4-bromobutyric acid are reported. Raman spectra of the ν(C-Br) region for a range of concentrations below the critical micelle concentration have been interpreted in terms of $\text{gauche}$ C₄ - C₃ linkages becoming more dominant upon pre-micellar association. The results demonstrate the viability of using bromine substituted species in Raman studies of micelle formation.

SCF-MO calculations using a large atomic orbital basis set predict that both heterodimers C₂H₄S…HF and C₂H₄S…HCl are stable, with non-planar equilibrium geometries. Well depths, Mulliken population indices and several one-electron properties are reported for the heterodimers.

The conformational changes of aspartate induced by increasing ionic strength were investigated by means of NMR spectroscopy. The effects of Li, Na, K and Cs chlorides in basic solutions show a relative stabilization of the two conformers with gauche carboxylates at the expense of the anti conformer. A significant quantitative difference was found between Na⁺ and K⁺. The changes observed in neutral solutions, although larger than those in basic solutions, are dominated by the zwitterion interaction.

A qualitative and semiquantitative explanation of “double flash” photochemical behaviour of carbazole is found by means of Molecular Orbital studies of ground and excited states of carbazole and carbazyl radical using the CNDO/S method. The need to excite to quite high energy triplet states in order to produce the homolytic breakdown of N-H bond is justified by the fact that the triplet states of carbazole correlating with ground and first excited states of carbazyl radical are, respectively, T₁₅ and T₁₂. These triplet states appear to be populated indirectly by means of the second flash that at first populates some other nearby triplet states (T₉ to T₁₁) from T₁ followed by an Internal Conversion (IC) from these to the T₁₅ and T₁₂ states. This procedure is favoured by the energy lowering of the T₁₅ and T₁₂ triplet states on enlarging the N-H bond and by the important contamination of these two states owed to spin-orbit coupling.

The kinetics of exchange of the whole molecule between solvation sphere of Al³⁺ and bulk at Al(ClO₄)₃ in CH₃0D, CH₃CD₂0D and CD₃CH₂0D has been studied by means of line-shape analysis of PMR spectra of methyl and methylene groups. The activation enthalpy Δ H^≠ of 65 kJ/mol for methanol and 52 kJ/mol for ethanol were found. The exchange at 25°C is about 70 times faster for ethanol than for methanol.

The heats of dilution of ternary aqueous solutions of urea and alcohols have been determined at 25°C. From the experimental data the values of the excess enthalpies H_ij^E and of the pair enthalpy interaction coefficients h_ij have been evaluated and compared with the data reported in the literature. The values of the h_ij coefficients at 25°C are all positive and depend on the length and branching of the alkyl chain of the alcohols. The results are discussed in terms of the effects of a chaotropic agent”, as urea, on the cospheres of mainly hydrophobic such as alcohols.

The ultrasonic attenuation in liquid nonanoic acid (pelargonic) is measured between 16 and 55°C. A single relaxation phenomenon is pointed out at 16 and 25°C, in the ultrasonic range. At 35, 45 and 55°C, two relaxation phenomena are evident. One of the two phenomena disappears in the solution state.

It is shown that the definition of a mutual viscosity between solvent and solute can both give information about the structure of the solution and explain the discrepancy between the viscosity of the solvent and the correlation time of the solute. As the viscosity is connected with the friction coefficient, its unambiguous determination is of great significance for the calculation of the relaxation time.