Femtosecond two-dimensional infrared spectroscopy: IR-COSY and THIRSTY

The femtosecond two-dimensional infrared (2D IR) spectroscopy that was recently developed shows great promise for determining the dynamics of molecular structure at ultrafast time scales that are hard to access by NMR and X-ray diffraction methods. This Perspective focuses on the IR-COSY and THIRSTY methods that are based on heterodyned three pulse photon echoes. The relationships of 2D spectral properties coupling, structure, correlated fluctuations, energy transfer, and orientational motions to experimental results on small peptides and molecules are described. The status of this exciting new field is also discussed.