Vibrational coupling within molecules can be studied by the all IR pump-probe technique, 2DIR spectroscopy. Analogous to the way 2D-NMR probes the coupling of nuclear spins within molecules, 2DIR looks at the way vibrational energy couples through molecules. The technique uses an IR pump pulse to excite molecular vibrations in a sample, then with IR absorption spectroscopy probes how the energy flows through the molecule on an ultrafast timescale.
Within Ultra, narrowband picosecond pump pulses are used to excite specific vibrations, the vibrational spectrum change is then probed with broadband femtosecond IR pulses. This method takes advantage of the unique dual picosecond/femtosecond output of the Ultra laser system. The 2DIR technique can be used to study ground-state or transient species, by photo-exciting the sample before recording the 2DIR spectrum.
Applications of the technique range from investigation of fundamental chemical dynamics to unravelling large biological systems where IR spectra are congested.