Knowledge Bank

The absorption spectrum of the lowest triplet state of trans-stilbene is observed between 14 kK and 18 kK in a crystal 4 cm long cooled to $4.2\circ K$. The spectrum shows the following properties of trans-stilbene in the lowest triplet state: 1. The oscillator strength is $(3\pm 2)\times 10-9$, which is about an order of magnitude larger than the triplets in ordinary aromatic compounds. Most of the intensity is induced vibronically by an out-of-plane vibration. 2. Seven normal modes in the triplet are identified in the spectrum. 3. Lines in the spectrum are broad (8 K), probably due to unresolved exciton structures.