The phonon structure, triplet exciton splitting and predissociation of p-diiodobenzene

The singlet-triplet absorption spectrum of pure p-diiodobenzene crystals is shown to be dominated by phonon sidebands. The intensity and extent of this progression is attributed to predissociation of the lowest triplet state. In view of these findings, it does not seem necessary to assume, as has been done previously, that p-diiodobenzene has a large triplet exciton bandwidth. © 1975.