Two-dimensional Raman spectroscopy of the intermolecular modes of liquid CS2

Abstract

The two-dimensional response of the intermolecular modes of CS2 has been measured using nonresonant fifth order Raman spectroscopy. Whereas third order Raman spectroscopies only observe the spatially averaged spectrum of solvent motions, the fifth order experiment allows the microscopic 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 structures at short times (<300 fs), and by spatially uniform structural relaxation 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 obtained by virtue of the full two-dimensional response. The ability to make such observations has important general implications for understanding the broad range of time scales in the study of dynamics in complex condensed phases.