Femtosecond Fourier-transform spectroscopy of low-frequency intermolecular motions in weakly interacting liquids.

摘要

Recent work on the subject of solvation dynamics has concentrated on understanding the ultrafast dynamics of intermolecular interactions in strongly interacting, polar, and hydrogen-bonding solvents. In general, investigations into the effects of solvation dynamics on chemical reactions have concentrated on the highly polar liquids because it is in these solvents that the largest spectroscopic changes with solvent relaxation are observed. In these very polar liquids, however, the intermolecular dynamics are very complex, consisting of contributions from reorientational diffusion, inertially limited rotations, intermolecular vibrations involving both reorientational (librational) and translational degrees of freedom, and interaction-induced collisional effects. The role of collisional interaction-induced effects in shaping the intermolecular dynamics of molecular liquids has been a subject of considerable discussion. Molecular dynamics simulations have suggested that collisional effects can have a significant role in shaping the femtosecond dynamics and nonlinear-optical properties of molecular liquids. However, for anisotropic molecules, it is difficult to separate experimentally the collisional effects from other phenomena. In this paper the authors examine the intermolecular dynamics of the weakly interacting liquid carbon tetrachloride (CCl(sub 4)). Because carbon tetrachloride is a spherical top molecule (belonging to the T(sub d) point group), its intermolecular light-scattering spectrum is purely interaction-induced. By studying this purely collision-induced feature in CCl(sub 4), the authors hope to gain insight on the lowest-frequency intermolecular vibrational behavior of more complex systems.