Advances in Molecular Relaxation and Interaction Processes最新文献

The relative permittivity at frequencies of 10kHz and 10GHz and the refractive indices have been measured for dilute solutions of (a) nitroethane, (b) 1-nitropropane, (c) 2-nitropropane, and (d) 1-nitrobutane in cyclohexane at 10°, 20°, 30° and 40°C. Materials (b) and (c) together with (e)2-nitro 1-propanol and (f) 2-nitro-l-butanol, have also been studied in different nonpolar solvents. The electric dipole moments, the dielectric relaxation times, and the molar activation energy parameters have been calculated. The results for nitroalcohols show the existence of internal hydrogen bonding between the hydroxyl group and an oxygen atom of the nitro group. The plots of log τ versus log η for materials (b) and (c) are linear for the solvents n-heptane, cyclohexane and decalin. The possibility of interaction of these materials with p-xylene, carbon tetrachloride and p-dioxane are discussed. Activation enthalpy (ΔH_ε) of these materials is observed to be higher in dilute solutions than in pure liquids, and also ΔH_ε for nitrobutane is significantly lower than for the other materials.

The complex electric permittivity and viscosity over the frequency range 100 MHz-2GHz have been measured for the propionic acid- tri-n-butylamine systems of varying composition. Both, the value of the relaxation time and its distribution indicate a remarkable aggregation especially for 1:1 species.

The orientational order parameter S₂ for homeotropic and homogeneous 4-cyano-4′-alkyl and alkoxybiphenyls was calculated and its temperature dependence in smectic A and nematic phase was studied.

From Brillouin spectra of tetrachloromethane, benzene and cyclohexane measured between 283.15 K and 343.15 K, and carefully re-evaluated data for the heat capacities at constant pressure C_P, and constant volume C_V, the vibrational contribution to C_V was determined and compared with calculated values obtained from the Planck-Einstein relation. Utilizing perfect gas state heat capacity data, the residual heat capacity C_V^* wa determined and subsequently used to present an estimate for the residual rotational heat capacity (external rotation).

The interaction of p-nitrophenol with several electron-donors has been studied in aprotic and protic solvents by electronic absorption spectroscopy. The equilibrium data for different kinds of equilibria in 1,2-dichloroethane, n-butanol and acetonitrile have been obtained and discussed. The strong hydrogen bonding interaction between p-nitrophenol and a variety of electron donors has been investigated in heptane by electronic absorption spectroscopy. The interesting correlations obtained in terms of Mulliken's charge transfer model have been examined and extended in many cases.

Dielectric spectra of formyl-, carboxyl-, and 1,1′-dichloro-ferrocene have been examined in benzene in the frequency range of 100 MHz-26 GHz, at various temperatures. In these conditions only one clear dielectric absorption band has been observed and a Debye-type behaviour has been found. Calculation of the macroscopic dielectric relaxation times and the thermodynamic parameters has also been performed. All evidence seems to suggest a type of mechanism for dielectric relaxation, even if at the present stage of research it might be prudent not to indicate a definitive model for the molecular dynamics itself of these compounds.

The temperature dependence of the rotational diffusion in liquid CH₂Cl₂ has been measured in the far infrared from 10 to 220 cm⁻¹ and 177K to 313K (f.p. to b.p. at 1bar). The results are interpreted at 177K and 293K with a molecular dynamics simulation using a 5 × 5 atom-atom potential with charge-charge electrodynamics. The simulation reproduces the basic features of the spectra but some experimental detail of the dependency of

Large basis set $\text{Ab}$ $\text{Initio}$ calculations are reported for the variation of energy and electric dipole moment with internuclear separation for the diatoms ArHe and NeHe. Electron correlation effects are treated explicitly by the self consistent electron pairs method, and are found to be large. The effect of basis set superposition is examined, and found to be significant. Calculated potential well depths D_e and equilibrium internuclear separation R_e compare with the ε_m and R_m values found by fitting various experimental data. The electric dipole moment p_e for the ArHe diatom at distances ≈ RI_e is larger than that for the NeHe diatom, in accordance with the fact that the full collision induced absorption spectrum has been observed experimentally only for the latter. The variation of p_e with R shows fine structure at R ≈ R_e not previously reported.

Addition of increasing amounts of phenylalanine in dilute aqueous solutions of adenine, theophilline, theobromine, caffeine and tetramethyluric acid induces proton chemical shift changes that can be interpreted on the basis of the existence of 1:1 complexes. Their formation quotients are comparable to those of the analogous complexes formed by purines with benzene in apolar solvents. Differences among formation quotients of a given complex, extracted from different nuclei of the purine, hint that 1:2 or higher complexes may be present, but the extremely narrow concentration range accessible for the donor compound prevents an accurate numerical analysis of these equilibria.