2-DIMENSIONAL RAMAN-SPECTROSCOPY OF THE INTERMOLECULAR MODES OF LIQUID CS2

The two-dimensional response of the intermolecular modes of CS2 has be en measured using nonresonant fifth order Raman spectroscopy. Whereas third order Raman spectroscopies only observe the spatially averaged s pectrum of solvent motions, the fifth order experiment allows the micr oscopic composition of this spectral density to be probed. Within the limitations of the theory, the results confirm a picture of the liquid CS2 in which dynamics are dictated by a distribution of fixed structu res at short times (<300 fs), and by spatially uniform structural rela xation at long times (>700 fs). The data suggest that the microscopic dynamics show highly damped oscillatory behavior at intermediate times . The full sensitivity to the details of the molecular dynamics is obt ained by virtue of the full two-dimensional response. The ability to m ake such observations has important general implications for understan ding the broad range of time scales in the study of dynamics in comple x condensed phases. (C) 1997 American Institute of Physics.