Selective detection of intermolecular response in benzonitrile through double-pulse excitation in optical Kerr effect spectroscopy

We report on the decomposition of the molecular contribution to the optically heterodyne-detected optical Kerr effect (OHD-OKE) in benzonitrile C 6 H 5 CN in the process of double-pulse laser excitation. The pump pulses with linear orthogonal polarizations, controllable intensities and timing enable us to manipulate the amplitudes of various molecular responses due to the fact that the OHD-OKE signal is formed by the superposition of independent third-order responses associated with each pump pulse. We apply this technique to detect the intermolecular response selectively by using an excitation scenario with suppression of orientational and intramolecular responses. A detailed comparative analysis of third-order optical responses indicates strongly that the double-pulse excitation of the OHD-OKE is the useful spectroscopic technique to obtain precise information on the intermolecular spectrum in liquids.