Two-Dimensional Infrared Spectroscopy
Two-dimensional infrared spectroscopy (2DIR) is a nonlinear infrared spectroscopy technique, investigating vibrational modes in condensed-phase systems. The technique provides information beyond linear spectra by spreading the vibrational information along multiple axes. This yields a frequency correlation spectrum with information on vibrational mode coupling, as well as chemical and molecular dynamics with femtosecond resolution.
According to Gelžinis et al., the key strengths of 2D spectroscopy include the following:
- The uncoupling of time and excitation frequency resolution allows researchers to follow specific states’ dynamics with selective excitation and excellent time resolution.
- The lack of background signals allows achieving an excellent signal-to-noise ratio.
- A single run of 2D spectroscopy provides information with a wide range of excitation frequencies, while using the pump-probe technique requires many separate measurements.
For the last fifteen year 2D spectroscopy has contributed heavily to our understanding of excitation dynamics in photosynthetic molecular complexes. It is a safe bet that it will continue to do so for the foreseeable future.
Two-dimensional infrared spectroscopy experiments have become possible with the development of ultrafast lasers, such as PHAROS and CARBIDE, and the ability to generate femtosecond infrared pulses, e.g., using the ORPHEUS-MIR broad bandwidth mid-IR source.
Two-dimensional spectroscopy can also be applied in the VIS spectral range, where electronic states are investigated; see two-dimensional electronic spectroscopy (2DES).
