OPTICAL-ABSORPTION SPECTRA OF THE DIMER-TYPE RADICAL IN IRRADIATED NAPHTHALENE SINGLE-CRYSTALS

Highly resolved optical absorption spectra of the radiation-induced radical having prominent optical absorption lines around 710 nm in a naphthalene single crystal have been studied. It is found that the aggregate lines around 710 nm comprise a few site-split zero-phonon lines, a phonon sideband and hot absorption lines. The vibrational progression, each component of which consists of similar group of lines as described above, is observed. The hot absorption lines are also found to be associated with some component of the vibrational progression. From the temperature dependence of the intensity of the hot absorption lines, it is found that they are coupled with phonons of 11 and 36 cm-1, which are ascribed to the local modes. The number of vibrational lines coupled with the 710 nm transition is found to be larger than the number of lines coupled with the lowest transition of the 1-hydronaphthyl radical, and it is pointed out that the vibrational frequencies associated with the 710 nm transition agree approximately with either those of the 1-hydronaphthyl radical or the naphthalene molecule. The present experimental results support the previous suggestion that the 710 nm lines arise from a dimer-type radical, the conclusion having been deduced from the observation that the radical is formed not directly by irradiation at low temperatures but by thermal annealing at room temperature of a specimen irradiated at low temperature. © 1979.