Off-Resonant Fifth-Order Response Function for Two-Dimensional Raman Spectroscopy of LiquidsCS2andH2O

The off-resonant fifth-order response functions for two-dimensional (2D) Raman spectroscopy of molecular liquids ${\mathrm{CS}}_2$ and ${\mathrm{H}}_2\mathrm{O}$ are investigated by using molecular dynamics calculation. This spectroscopy, able to deal with a phase space dynamics, shows the existence of nodal lines in several polarization tensor elements [see L. Kaufman et al., Phys. Rev. Lett. 88, 207402 (2002) for experimental results]. The nodal property is found to arise from the dynamical couplings among rotational modes, not accounted for in a normal mode picture. The effects of anharmonicities and “mode coupling through polarizability” are also investigated by comparing the 2D Raman signal with a constant temperature velocity reassignment echo method.