Phosphorescence Spectra of Acenaphthene at Low Temperatures

The phosphorescence spectra of acenaphthene, both of single crystals and of solutions in different solvents (polystyrolene, benzene, or E.P.A.), were photographed at low temperatures. At 4° and 77°K unpolarized spectra of the crystal were obtained using a phosphoroscope, and at 20°K the polarized spectra along the three crystallographic axes had been photographed without the phosphoroscope. Some peculiarities linked to the existence of two different sets of molecules in the unit cell have been observed. Two progressions, here called ``normal,'' connected to each set of molecules have been distinguished in the 4° and 77°K spectra but not in the 20°K spectrum. The interval between the corresponding bands of the two progressions is 28 cm—1. In the 20°K spectrum two new series, here called ``nonnormal,'' and which appear also in the 77°K spectrum have been observed. An attempt of interpretation of these ``nonnormal'' series has been advanced.