Knowledge Bank

On the basis of infrared and ultraviolet absorption studies of phenol vapor and some of its isotopes, it has been shown that the vibronic states of phenol, a non-rigid molecule, can be classified according to the species of $Cte$. All 13 totally symmetric vibrations $(a1)$ have been identified in the excited state $(\ast B2)$ and improved values have been obtained for ground state $(\ast A1)$ fundamentals occurring below $1300cm-1$; the excited state ring modes have also been correlated with the modes of benzene. The $b2$ vibrations appear in the electronic spectrum as a ``forbidden'' system with z-polarization. Low-frequency out-of-plane vibrations are responsible for strong sequences. The assignment of torsional mode in the $\mathrm{<mrow\; data-mjx-texclass="ORD">\ast </mrow>}B2$ state, the relative intensities of totally-symmetric fundamentals and their progressions, the double-quantum changes of non-totally symmetric vibrations and the band envelopes associated with the $a1$ and single-quantum $b2$ vibrational changes in the electronic spectrum, all provide significant information about the structure of phenol in its first excited state.