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The intramolecular degrees of freedom contributing to the ultrafast excited-state intramolecular proton transfer of 1-hydroxy-2-acetonaphthone are determined. Thereto, resonance Raman studies are combined with transient absorption measurements with 30-fs time resolution. Enhanced Raman intensity is found in coordinates that are dominantly associated with deformations and bond length changes in the naphthalene chromophore. This indicates that the primary changes after the optical excitation are a geometric relaxation of the chromophore. A ringing of the molecule after the ultrafast proton transfer is observed by the transient absorption measurements. It reveals the nuclear coordinates contributing to the reaction path beyond the Franck-Condon region. There, planar H-chelate ring deformations changing the donor-acceptor distance are found to dominate. The difference in the observed vibrational signatures indicates a significant turn in the reaction path.

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