Intermolecular interaction-induced quantum beats in femtosecond time-resolved light scattering from molecules: photon-polarization and inhomogeneous effects Original Research Article

We present a quantum statistical theory of intermolecular interaction-induced quantum beats in ultrashort time-resolved light scattering (TRLS) from an ensemble of two interacting molecules (chromophores). An expression for the profile of TRLS is derived based on the generalized master equation in Liouville space. The expression takes into account the initial excitation process as well as the dephasing process. Model calculations of femtosecond TRLS profiles in resonant conditions and an intermolecular degree of coherence are performed to show how the quantum beats appear as a result of intermolecular coherent energy transfer. Effects of photon-polarization on the TRLS profile are investigated. It is shown that under the magic angle condition the interaction-induced quantum beats disappear regardless of the relative orientation between two interacting molecules. Effects of inhomogeneity in interacting molecular pairs on the TRLS profile are also investigated. Finally, inhomogeneity effects on the quantum beats in time-dependent anisotropic absorption observed by Zhu et al. (J. Chem. Phys. 98 (1993) 1042) are discussed.