ABSTRACT
The 2D vibrational spectroscopic technique based on four-wave-mixing schemes has certain advantages in comparison with conventional 1D vibrational spectroscopy such as IR absorption, Raman scattering, vibrational circular dichroism, and the like.1-5 Due to the doubly vibrationally resonant condition, IR fields different in frequency can be simultaneously resonant with two different vibrational degrees of freedom, and consequently, cross-peaks in a two-dimensionally displayed spectrum arise from their couplings that are usually difficult to be measured by using 1D method (compare the magnitudes of primary and secondary spectroscopic properties mentioned in Chapter 1). In addition, the two oscillators have to be anharmonic to avoid complete destructive interferences among different nonlinear optical transition pathways. Note that the nonlinear response function of perfectly harmonic oscillators vanishes.
