Dielectric spectra were measured for eight, mostly imidazolium-based, room temperature ionic liquids (RTILs) over a wide range of frequencies (0.2 < or = nu/GHz < or = 89) and temperatures (5 < or = theta/degrees C < or = 65). Detailed analysis of the spectra shows that the dominant low frequency process centred at ca. 0.06 to 10 GHz (depending on the salt and the temperature) is better described using a symmetrically broadened Cole-Cole model rather than the asymmetric Cole-Davidson models used previously. Evaluation of the temperature dependence of the static permittivities, effective dipole moments, volumes of rotation, activation energies, and relaxation times derived from the dielectric data indicates that the low frequency process cannot be solely due to rotational diffusion of the dipolar imidazolium cations, as has been thought, but must also include other contributions, probably from cooperative motions. Analysis of the Debye process observed at higher frequencies for these RTILs is not undertaken because it overlaps with even faster processes that lie outside the range of the present instrumentation.

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Dielectric spectra have been measured for aqueous sodium dodecylsulfate (SDS) solutions up to 0.1 mol L-1 at 25 degrees C over the frequency range 0.005 < or = nu GHz-1 < or = 89. The spectra exhibit two relaxation processes at approximately 0.03 GHz and 0.2 GHz associated with the presence of micelles in addition to the dominant solvent relaxation process at approximately 18 GHz and a small contribution at approximately 1.8 GHz due to H2O molecules hydrating the micelles. Detailed analysis reveals that the micelles bind 20 water molecules per SDS unit, but not as strongly as trimethylalkylammonium halide surfactants do. The relaxation times and amplitudes of both micelle relaxation processes can be simultaneously analysed with the theory of Grosse, yielding the effective volume of a SDS unit in the micelle and the lateral diffusion coefficient of the bound counterions. The findings of this investigation fully corroborate recent molecular dynamics simulations on structure and dynamics of SDS micelles.

Dielectric relaxation measurements as a function of temperature, and of concentration in a non-coordinating solvent, the first reported for an ionic liquid, indicate a crossover in the relaxation mechanism due to varying levels of ion aggregation and the interplay of formation kinetics and relaxation dynamics of associates.

This work presents a study of carboxylate adsorption at the fluorite/water interface by vibrational sum frequency spectroscopy. A homologous series of monocarboxylic ions including formate, acetate, propionate, hexanoate, and dodecanoate was studied in frequency regions corresponding to the νCH and νCO/δCH response. Previously reported vibrational and Raman modes were investigated for their sum frequency activity. For a more reliable band assignment, sum frequency measurements on systematically deuterated compounds were completed and compared with calculated band positions and intensities. Different polarization configurations were utilized, together with symmetry properties of bands derived from a normal-mode analysis, to classify the observed fundamentals and overtones. Differences in chain length led to striking changes in the spectral signatures of the compounds studied and were related to the molecular structure of the adsorbates and interfacial water molecules.