Alessandra Scodinu

Exponential intermolecular dynamics in optical Kerr effect spectroscopy of small-molecule liquids

Optical Kerr effect spectroscopy has been employed to study the behavior of six symmetric-top liquids (acetonitrile, acetonitrile-d3, benzene, carbon disulfide, chloroform, and methyl iodide) over a broad range of temperatures. In all of the liquids, an exponential intermolecular response is observed on a time scale of a few hundreds of femtoseconds. Comparison of the temperature dependence of the time scale of this relaxation with the viscosity and single-molecule and collective orientational times in the liquids suggests that the exponential relaxation arises from motional narrowing.

Dynamics of a wetting liquid in nanopores: An optical Kerr effect study of the dynamics of acetonitrile confined in sol-gel glasses

The orientational dynamics of acetonitrile and acetonitrile-d3 confined in nanoporous glasses have been studied using optical Kerr effect spectroscopy. The decays can be fit to the sum of three exponentials, the fastest of which corresponds to relaxation of bulk-like liquid. We present evidence that the intermediate exponential arises from the exchange of molecules bound to the pore surfaces into the bulk liquid, whereas the slowest exponential corresponds to surface relaxation. A comparison to nuclear magnetic resonance data demonstrates that the liquid at the pore surfaces is more highly ordered than that in the bulk. Surface-modification studies demonstrate that hydrogen bonding is responsible for the extreme inhibition of dynamics at the pore surfaces.

Temperature-dependent optical Kerr effect spectroscopy of chloroform in restricted geometries

Abstract Optical Kerr effect spectroscopy has been used to study the orientational dynamics of chloroform confined within nanoporous glasses of various pore sizes. The decays can be fit well to the sum of two exponentials, the fastest of which has a decay time that matches that of the bulk liquid. Based on these data, we have quantified the surface population and the dynamics of the confined liquid. We have also studied the dynamics of the Raman-active degenerate CCl 3 deformation mode at 262 cm −1 and the symmetric CCl 3 stretch at 365 cm −1 , both of which show shifts to higher frequency in confinement. The shifts decrease as the temperature decreases. Pure dephasing and population relaxation at the pore walls appear to dominate the spectral line shapes at lower temperatures, resulting in a decrease in the dephasing time in confinement. At higher temperatures, the line shape is dominated by rotational broadening.