Vibrational excitation and energy redistribution after the ultrafast intramolecular proton transfer cycle of TINUVIN was investigated by picosecond pump-probe resonance Raman spectroscopy. Our studies demonstrate that the line shape function of the resonance Raman cross section dramatically changes due to vibrational excitation. Therefore, instead of determining vibrational populations directly from anti-Stokes resonance Raman kinetics, excitation of the modes has been characterized by their time-dependent ratios of anti-Stokes and Stokes resonance Raman intensities. Using this novel approach it is shown that a low-frequency proton transfer promoting mode serves as a major accepting mode of the proton transfer cycle. (C) 2004 Elsevier B.V. All rights reserved.