Knowledge Bank

The absorption spectrum of 9-fluorenone has been examined in pure and mixed crystals from 4700 to 3000 \AA at low temperatures. The lowest state has been assigned as a long axis polarized $\pi \ast \leftarrow \pi$ transition. This state remains broad at 4.2$\mathrm{<mrow\; data-mjx-texclass="ORD">\circ </mrow>}K$ indicating a large amount of vibronic mixing with a nearly degenerate $(n\pi \ast )$ state. A second $(\pi \pi \ast )$ state has been observed in the 3400 to 3000 \AA region.