Knowledge Bank

Hydroquinone and p-dimethoxybenzene exist in cis $(C2v)$ and trans $(C2h)$ isomers. The isomer (symmetry) and the energy dependence on the onset of intramolecular vibrational redistribution (IVR) was infered using dispersed fluorescence spectra. In the case of hydroquinone it was observed that both the isomers exhibit the same energy dependence on the IVR, and is evident at energies $\sim 1700cm-1$. However in the case of p-dimethoxybenzene, the onset of IVR for the cis isomer was observed at $\sim 900cm-1$, and that for trans isomer at $\sim 1300cm-1$. The extent of the state mixing in the $S1$ state within the harmonic approximation was calculated using time dependent coupled cluster method. The experimental and the theoretical results will be compared and the validity of the harmonic approximation on the state mixing vis-a-vis the observed isomer dependent IVR behaviour will be discussed.