Water Structure around Hydrophobic Solutes Water Structure around Hydrophobic Solutes by Femtosecond 2D-Vibrational Spectroscopy Mark A. Berg, Department of Chemistry and Biochemistry, University of South Carolina Solutes in water create distortions of the hydrogen-bond network. The distortions drive hydrophobic effects, solubility, self-assembly and protein folding. A new type of multiple-pulse spectroscopy is being developed to measure the structure of the distorted water next to a solute: IR pulse 1 excites a solute vibration – IR pulse 2 uses a proximity-induced transition to transfer coherence to a nearby water molecule – coherent Raman scattering of a visible pulse yields the Raman spectrum of the solute-perturbed water. coherent Raman signal IR pulse 1 IR pulse 2 visible pulse The first focus of the project has been the final step of the experiment – measuring coherent Raman spectra with femtosecond pulses. A new approach based on simultaneous detection in time and frequency has been demonstrated. This method allows any coherent Raman experiment to be extended to the femtosecond range: CARS microscopy, Raman-detected photochemistry, surface-sum-generation spectroscopy; as well as enabling our own experiment. Introducing the IR pulses to our experiment is now underway.