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.

A new skewed-arc alternative to the Davidson-Cole permittivity function is derived. It has the same very low and very high frequency limit angles in its Cole-Cole arc and approaches the behavior of the Davidson-Cole permittivity function for small values of the exponent parameter β. The difference, however, becomes increasingly appreciable for large values of β. The distribution function g(ln τ) is very much like that for the Davidson-Cole system, but it does not exhibit any singular nor discontinuous slope behavior for any value of the relaxation time τ.

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.

With our Kerr-effect apparatus, measurements in nanosecond domain are possible. Thus dynamic Kerr effect and dielectric relaxation studies have been made for glycerol in the range 268-258°K. Measurements show that τ_k = τ_d and we deduce a structural relaxation. The “spike” obtained immediately following the step removal of E is also analysed.