Mode coupling mechanisms in the impulsive 2D Raman response of liquid CS2

The 2D Raman response of CS2 is dominated by slow diffusive dynamics along the first propagation time while it is determined by ultrafast inertia-limited motions along the second time variable. These features cannot be explained when the reorientational diffusion and coherent intermolecular vibrations are modeled as independent processes. Mode coupling induced by the nonlinear polarizability can partly reproduce the observed asymmetry but yields wrong predictions at early times. Mode coupling by anharmonic interactions cannot even qualitatively account for the experimental data. An improved description of interaction-induced effects and cage dynamics is required for a better understanding of the 2D Raman response.