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: a vibrational IR pulse excites a solute vibration – a near IR pulse 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 Vibrational IR pulse Near IR pulse Visible pulse In the first phase of this project, a new method was developed to detect the coherent Raman signal with femtosecond pulses. In the second phase of the project, a new set-up has been built to generate the three excitation pulses and to bring them to the sample with the correct relationships in time, space and polarization. These requirements are challenging because the pulses are spread over very different spectral regions: vibrational IR, near IR and visible. The X-FROG traces to the left show success in combing these pulses at the sample while retaining good pulse properties.