Theoretical description of two-dimensional vibrational spectroscopy by infrared-infrared-visible sum frequency generation

The two-dimensional infrared-infrared-visible (IIV) sum frequency generation (SFG) is theoretically considered. IIV-SFG is a two-dimensional extension of the infrared-visible SFG, since it involves two vibrationally resonant infrared fields of which frequencies are experimentally controlled. An additional visible field is used to probe the vibrational coherence dynamics. This IIV-SFG technique can be used in studying intramolecular and inlermolecular vibrational interactions in isotropic condensed phases as well as on surfaces and interfaces. Due to the selection rules that are quite different from the one-dimensional vibrational spectroscopies, the IIV-SFG signal intensity is determined by the vibrational anharmonic couplings and nonlinearities of the polarizability and dipole moments with respect to the vibrational coordinates. In particular, for a model system consisting of two neighboring molecules or subgroups in a macromolecule, how the spatial and structural information can be extracted from the IIV-SFG measurement is discussed.