Abstract
The fluorescence spectrum of extremely purified and good anthracene crystals has been remeasured. It is compared with the exciton band structure as calculated by Davydov and Sheka. The origin of the intrinsic fluorescence is at 25 097 cm-1. This is the lower edge of the exciton band with k ≠ 0. Therefore this 0.0-transition is forbidden. The allowed 0.0.transition of the lower Davydov component of the exciton band is observed at 25 298 cm-1 with very low intensity. This is the position of the very short living state k = Q (Q=photon wave vector) in the exciton band. Further observations concerning the structure and temperature dependent width of emission lines, the nature of exciton-phonon and exciton-vibron coupling and the large band width in absorption are also in good agreement with the calculated band structure. The polarization ratio of the strongest vibronic transitions is 7.5 ± 1 good agreement with the oriented gas model. The spectral region near the forbidden 0.0-transition is completely 6-polarized. Effects of defects in the spectrum (series of lines due to impurities and X-traps, continuous background) were widely eliminated. They are discussed here only as far as necessary for a better understanding of the unperturbed crystal spectrum. In an appendix a list of 154 fluorescence lines is given.
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