Nonlinear response functions for the three-dimensional spectroscopies

The three-dimensional response function, which describes any 3D vibrational, 3D vibrational-electronic, or 3D electronic spectroscopic processes, is theoretically considered by fully taking into account the system-bath interaction. The resultant expression of the 3D response function is sufficiently general to describe the vibrational rephasing process as well as other vibrational pump-probe spectroscopies. Furthermore, theoretical descriptions of the two-color IR photon-echo, three-dimensional sum- and difference-frequency generation, and two-color IR pump-probe methods are discussed and their advantages over the conventional IR photon-echo and one-color IR pump-probe methods are clarified.