Multidimensional Spectral Fingerprints of a New Family of Coherent Analytical Spectroscopies.

Triply resonant sum frequency (TRSF) and doubly vibrationally enhanced (DOVE) spectroscopies are examples of a recently developed family of coherent multidimensional spectroscopies (CMDS) that are analogous to multidimensional NMR and current analytical spectroscopies. CMDS methods are particularly promising for analytical applications because their inherent selectivity makes them applicable to complex samples. Like NMR, they are based on creating quantum mechanical superposition states that are fully coherent and lack intermediate quantum state populations that cause quenching or other relaxation effects. Instead of the nuclear spin states of NMR, their multidimensional spectral fingerprints result from creating quantum mechanical mixtures of vibrational and electronic states. Vibrational states provide spectral selectivity, and electronic states provide large signal enhancements. This paper presents the first electronically resonant DOVE spectra and demonstrates the capabilities for analytical chemistry applications by comparing electronically resonant TRSF and DOVE spectra with each other and with infrared absorption and resonance Raman spectra using a Styryl 9 M dye as a model system. The methods each use two infrared absorption transitions and a resonant Raman transition to create a coherent output beam, but they differ in how they access the vibrational and electronic states and the frequency of their output signal. Just as FTIR, UV-vis, Raman, and resonance Raman are complementary methods, TRSF and DOVE methods are complementary to coherent Raman methods such as coherent anti-Stokes Raman spectroscopy (CARS).