Knowledge Bank

The vibrationally resolved $S1\leftarrow S0$ electronic spectra of 1,3- and 1,4-divinylbenzene each exhibited two origin bands that are $\mathrm{<mrow\; data-mjx-texclass="ORD">\sim </mrow>}800cm-1$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">\sim </mrow>}1000cm-1$ apart respectively. Intrigued by this observation, we have recorded the different bands at full rotational resolution in a molecular beam. Analyses of these data show that the two bands are the $S1\leftarrow S0$ of the different conformers, cis and trans, in each molecule, which are remarkably far apart. Typically, such systems exhibit more closely spaced origin bands. A model that accounts for this unexpected behavior will be discussed.