Two-color pump-probe spectroscopies of two- and three-level systems: 2-dimensional line shapes and solvation dynamics

For both two- and three-level systems, theoretical descriptions of two-color transient grating, transient dichroism, and transient birefringence spectroscopies were presented. The two-dimensional line shapes of these pump-probe spectra were found to be strongly dependent on the solvation dynamics. The two-dimensional contours of the transient birefringence signal of a two-level system are not vertically directed in the short time region. The inverse slope of the tangential line of the two-dimensional contours was found to be linearly proportional to the solvation correlation function. The two-dimensional transient grating and dichroism spectra are shown to directly provide quantitative information on the reorganization energy and spectral diffusion dynamics. For a three-level system that is a model for an anharmonic oscillator, the peak separation observed in a two-dimensional transient dichroism spectrum was found to be determined by both fluctuation amplitude of the transition frequency and spectral bandwidth of the probe pulse. The transient dichroism and birefringence contours of a three-level system were also found to be tilted in the short time region. We, in the present paper, established a variety of relationships between two-dimensional pump-probe line shapes and solvation correlation function.