Knowledge Bank

The $S0$ $\leftrightarrow$ $S1$, and $So\leftarrow$$T1$ spectra of benzene dissolved in borazine crystals have been studied at 4.2$\mathrm{<mrow\; data-mjx-texclass="ORD">\circ </mrow>}K$ and compared with the spectra of pure and isotopically mixed benzene crystals. The photoexcitation method was used to observe very weak vibronic transitions in the $So\leftarrow$$S1$ spectra of the dilute mixed crystals. The spectra are sharp; in the $So\leftarrow$ $T1$ spectra, linewidths are of the order of $2cm-1$, Thus, the benzene dissolves substitutionally in the borazine crystal. The gas to crystal shifts for the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}B20$ states of the $C6H6D6-0$ isotopic molecules in borazine are measured and compared to the values for isotopic mixed crystals. Changes in frequency and intensity of the spectra indicate a slightly different configuration of the benzene molecule in the borazine matrix and the pure crystal. The weakness of phonon intensities indicates that the molecule in the excited state keeps the same orientation as in the ground state.