The femtosecond fifth-order nonlinear response of nuclear motion in liquids

The femtosecond fifth-order nonlinear response of CS2 is measured using nonresonant six-wave mixing. This method provides new information on the dephasing mechanisms of coherently excited nuclear motion that is not accessible in third-order experiments. Our experimental results indicate that the ultrafast librational motion in CS2 is overdamped and predominantly homogeneously broadened. The results deviate from those of Tominaga and Yoshihara and can be explained only partly within the model of Tanimura and Mukamel.