Triply
Resonant Sum Frequency Spectroscopy: Combining
Advantages of Resonance Raman and 2D-IR
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Abstract
This
article describes the new multidimensional spectroscopy technique
triply resonant sum frequency spectroscopy, a four-wave mixing technique
sharing advantages of both 2D-IR and resonance Raman experiments.
In this technique, lasers with three independent frequencies interact
coherently within a sample and generate an output frequency at their
triple summation. The output intensity depends on coupled electronic
and vibrational resonances in the sample. We use an organic dye as
a model system to demonstrate fully resonant, fully coherent multidimensional
spectroscopy using two independently tunable mid-infrared vibrational
interactions and one visible electronic interaction. When the pulses
are time ordered, the method has a single coherence pathway, eliminating
interference between pathways. Fundamental vibrational transitions
appear on one axis and overtones and combinations bands on the other,
allowing anharmonicities of the modes to be determined easily and
conveying molecular coupling information. The experiments demonstrate
coupling between seven vibrational ring modes and an electronic state,
the resolution of a Fermi resonance, detection of low concentrations,
elimination of excitation pulse scattering and fluorescence, background
suppression of solvent and co-solutes, and observation of coherence
dephasing dynamics. The electronic resonance enhancements used in
this methodology are similar to the enhancements responsible for resonance
Raman spectroscopy and can be considered resonance 2D-IR spectroscopy