Knowledge Bank

The chemical timing $method1$ for obtaining picosecond time resolved fluorescence spectra was used to measure intramolecular vibrational redistribution (IVR) parameters in $S1$ p-fluorotoluene (pFT). These parameters were determined for several levels and compared to those for the corresponding levels in p-difluorobenzene $(pDFB)1$ pFT and pDFB have nearly identical $S1\leftarrow S0$ absorption spectra and aronatic ring vibrational frequencies but were found to have significantly different IVR parameters. This observation is consistent with previous qualitative results regarding vibrational level mixing in pFT and $pDFB2$. Possible causes for these differences include the reduction of molecular symmetry and the coupling of torsional to vibrational motions will be discussed.