Die Schwingungsstruktur der Shpolskii-Spektren von Anthracen, 9-Methyl-und 9,10-Dimethylanthracen in n-Hexan bei 77 K. I. Fluoreszenz / The Vibronic Structure of Shpolskii Spectra of Anthracene, 9-Methyl- and 9,10-Dimethylanthracene in n-Hexane at 77 K I. Fluorescene

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Abstract
The fluorescence spectra of anthracene, 9-methyl- and 9,10-dimethylanthracene in n-hexane at 77 K were measured. The Franck-Condon-Factors are evaluated using equilibrium geometries, vibrational frequencies and normal coordinates of the molecules in the ground and first excited singlet state which were calculated by the QCFF/PI-method. These results are then compared with experimentally determined frequencies and estimated intensities. The new vibronic lines in the fluorescence spectra of the methylated anthracenes correspond to totally symmetric vibrations, up to 1000 cm-1 originated mostly by mixing with out-of-plane vibrations of the atoms of the anthracene skeleton. Above 1000 cm-1 these vibrations which have greater projections of their normal coordinates on the internal coordinates of the methyl groups, are not visible as vibronic lines in the fluorescence spectra. The multiplet structures of the O-O-transitions are ascertained.

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