Ultrafast Proton Dynamics During Proton-Coupled-Electron-Transfer and Excited-State-Proton-Transfer Andrei Tokmakoff, Department of Chemistry, Massachusetts Institute of Technology Excited state proton transfer occurs from a number of polyaromatic amidines, where the proton transfer is mediated by the surrounding hydrogen-bonding network. We have performed a complete set of third order spectroscopies: transient grating, echo peak shift, pump probe and full 2D-IR surface in the electronic ground state of four doubly hydrogen-bonded dimers in solution. Whereas the linear spectra might be dominated by Fermi-resonances, the transient grating and echo peak-shift measurements have shown that the vibrational dynamics are dominated by the low-frequency inter-monomer stretching and twisting vibrations. Transient grating Echo peak-shift Frequency dispersed pump-probe experiments and 2D surfaces fully resolve the intricate beating pattern observed in the transient grating and echo peak-shift measurements and is completely explained by the hydrogen-bonding strength of the vibration. Energy is observed to flow from the NH modes into the Fermi-resonances and strong coherent beating is observed between the different cross-peaks. 2D-IR surface FT Pump-probe