Absorption Spectrum of Fluorbenzene in the Near Ultraviolet

The absorption spectrum of C6H5F at 2750–2380A was photographed in the first order of a three-meter grating spectrograph. As in C6H5Cl the band system corresponds to an electronic transition A1, B1. This is an allowed transition and the 0,0 band is stronger than in C6H5Cl because of the greater perturbation by the fluorine. Several progressions of totally symmetric vibrations are observed. The vibration whose excitation brings the corresponding benzene spectrum into appearance, and which shows up relatively intensely in C6H5Cl, appears in C6H5F but is not particularly prominent. In contrast to C6H5Cl, transitions to the carbon-halogen vibration in the upper electronic state are quite strong.