Two-dimensional vibrational spectroscopy. VII. Investigation of the vibronic and vibrational couplings by using novel triply resonant two-dimensional vibrational spectroscopies

A single vibrational coherence state can be created by using either vibrationally resonant infrared field-matter interactions or Raman transitions induced by the electronically off-resonant fields. Then, the two-dimensional (2D) vibrational coherence created by two such interactions can be probed by using electronically off-resonant optical pulse via scattering by the 2D transient grating. However, due to the off-resonant field-matter interactions during the probing process, the signal intensity is likely to be small. Thus, in this paper, the cases when the 2D transient grating is probed by electronically resonant optical pulse are theoretically considered and the associated nonlinear response functions are investigated. It turns out that these novel 2D vibrational spectroscopic methods utilizing an electronically resonant probe pulse can be used to study both the linear and quadratic vibronic coupling strengths of molecules in either isotropic or anisotropic condensed phases, in addition to the vibrational anharmonicity and nonlinearity of the coordinate dependencies of the dipole moment, polarizability, and hyperpolarizability. (C) 2000 American Institute of Physics. [S0021-9606(00)00142-2].