Brian J. Loughnane

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.

LEVEL-DEPENDENT DAMPING IN INTERMOLECULAR VIBRATIONS : LINEAR SPECTROSCOPY

A treatment of stimulated Raman intermolecular spectroscopy is presented that employs a Landau–Teller model of damping. This model incorporates a quantum-number dependence to population relaxation and pure dephasing, thereby introducing a specific temperature and frequency dependence into the damping in the intermolecular spectrum. Optical-heterodyne detected Raman-induced Kerr effect data obtained in CS2 and acetonitrile over a broad temperature range are shown to agree with the basic predictions of the model.

Temperature dependence of the dielectric function of C6H6(l) and C6H5CH3(l) measured with THz spectroscopy

We report on an experimental investigation of the temperature dependence of the intermolecular dynamics in liquid benzene and toluene. With the use of THz time domain spectroscopy we measured the complex dielectric function (0.2–3.3 THz) of the liquids, at temperatures between −6 °C and 75 °C. By analyzing the dielectric loss (as opposed to the absorption coefficient) we found three contributions to the dielectric function for toluene and two for benzene. In the dipolar liquid toluene we observed a contribution from rotational diffusion at lower frequencies in addition to the two high-frequency librations also observed in benzene. The temperature and density dependence were different for the two librational bands, probably due to the different effect of three-body interactions for the two processes. Furthermore, we present measurements of the low-frequency depolarized Raman spectra as a function of temperature for benzene and toluene. These have been compared with the dielectric loss at similar temperatur...

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.

Temperature-Dependent Dynamics of CS2: An OHD-RIKES Study

The intermolecular modes of liquids play a crucial role in chemical dynamics in solution, as has been demonstrated by numerous experimental [1] and theoretical [2] studies. A microscopic understanding of these modes is essential to the development of a coherent picture of solution-phase chemistry. For a given chemical process, one would like to know the physical nature of the relevant modes (e.g., whether they are predominantly rotational or translational) as well as their dynamic nature (i.e., whether they are homogeneously or inhomogeneously broadened). These issues have proven difficult to resolve even for bulk liquids, for which the intermolecular modes have traditionally been studied with variants of far-IR or depolarized Raman spectroscopy. These techniques are formally linear in the modes being studied, and therefore give no direct information about the nature or the broadening mechanisms of the modes.

Temperature-Dependent Dynamics of Microconfined Cs 2

Femtosecond optical-heterodyne detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) has been used to study the reorientational dynamics of CS 2 in microporous glasses over a wide range of temperatures. Microconfinement is shown to affect the behavior of the liquid at all the temperature studied. The results are interpreted in terms of a two-state model of the confined liquid.