Spectra of Benzil

The polarized low-temperature absorption spectrum, emission spectrum, and excitation spectrum of benzil and benzil-doped stilbene crystals have been recorded. It has been found that the 3800 Å (n–π*) band system of benzil is split by the weak interaction between the two halves of the molecule. The excitation spectrum reveals the presence of a S→T transition hidden underneath the S→S transition. The crystal spectrum of benzil-doped stilbene is different from the benzil spectrum. The new sharp band at 4850 Å has been interpreted in terms of a trans–planar configuration of benzil. A weak (π*→n) fluorescence has been detected in this crystal.