Knowledge Bank

“Detailed polarization of absorption studies of the near ultra violet band of p-di(dimethylamino) benzene have been carried out by the method of polarized photo-oxidation in dilute rigid glass solutions. The results follow a pattern found earlier in the crystal spectrum of p-dimethoxybenzene. In both instances short axis polarization is found in the zero-zero region corresponding to a $Bao$ assignment for the excited electronic state ($Vh$ symmetry assumed). In the higher energy region of the same band, however, the polarization of absorption reverses itself to become long axis polarized. It is not believed that two separate electronic bands are indicated. Instead it appears that here one is dealing with complete breakdown of the pure electronic selection rules. The neighboring $B1u$ electronic state must play an important role in any perturbation consideration. Some implications of these observations are discussed.”