Multiresonant coherent multidimensional spectroscopy.

Multiresonant coherent multidimensional spectroscopy is a frequency-domain method that uses tunable excitation pulses to excite multiple quantum coherences (MQCs) and/or state populations using fully coherent or partially coherent excitation pathways. Pairs of states that are coupled by intra- and intermolecular interactions re-emit light at their frequency differences. The MQCs are coherent and interfere constructively to create phase-matched output beams. Scanning the excitation frequencies with fixed-excitation-pulse time delays creates multidimensional spectra, whereas scanning the time delays with fixed excitation frequencies measures the MQCs' coherent and incoherent dynamics. Multiresonant methods can excite any combination of vibrational and/or electronic states and use any coherence pathway. Cross-peaks occur between states when the excitation of one perturbs the other. This requirement for coupling acts to eliminate spectral congestion. Spectral resolution is increased because multiresonant methods narrow inhomogeneous broadening, enhance peaks from specific components, and spread the resolution over multiple dimensions.