IVR in the S1 state of jet-cooled cis- and trans-p-dimethoxybenzene

Differences in the vibronic spectroscopy and IVR characteristics in the S1 state of cis and trans isomers of p-dimethoxybenzene (PDMB) were studied using a laser-induced fluorescence technique in supersonic jet expansion. Hole-burning spectroscopy was used to separate the transitions belonging to the individual isomers. In a few select modes the Franck–Condon activity in excitation and emission was different for the two isomers. The onset of IVR inferred from the dispersed fluorescence spectra was found at much lower energy for the cis isomer than that for the trans isomer. This was attributed to the difference in the electronic structure of the two isomers.