While ultrafast Infrared spectroscopies are valuable tools to study condensed phase structural dynamics, they are limited in terms of accessible concentrations. In order to develop a more sensitive Infrared vibrational spectroscopy, I have developed a set of multidimensional mixed-infrared-visible techniquesin which a vibrational excitation modulates the resonance of an electronic transition with an initially off-resonance encoding field. The resulting electronic excited state population can relax radiatively and the incoherently-emitted fluorescence can be detected with high sensitivity as the experimental observable.This class of fluorescence-encoded Infrared (FEIR) vibrational spectroscopies was demonstrated to be sensitive to vibrational coherences that result from an excited superposition of coupled modes in the encoding time delay between the respective vibrational and electronic excitations. In the case of FEIR that is linear in IR intensity, condensed-phase solvation measurements can report on the same processes as FTIR absorption at the lower concentrations accessible to fluorescence-detection, and higher orders of FEIR that are analogous to 2D IR can be predicted from a response function formalism. By demonstrating that coupled-vibrational information can be encoded into a fluorescence observable, this research lays the groundwork for high-sensitivity vibrational measurements at the dilute concentrations accessible with the detection of fluorescence.




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