Experimental measurement and calculation of the line intensities in vibronic spectra of jet-cooled anthracene

The intensities of vibronic lines are experimentally measured in fluorescen ce and fluorescence excitation spectra of jet-cooled anthracene. An origina l method is developed for calculating geometrical parameters of benzene hyd rocarbons in the ground and excited electronic states. Using these paramete rs, the intensities of vibronic lines in fluorescence and absorption spectr a of anthracene are calculated in the Franck-Condon approximation taking in to account the mixing of all the twelve normal coordinates of totally symme tric vibrational modes. After correction for the quantum yield of fluoresce nce, good agreement is obtained between the calculated line intensities in the absorption spectrum and the measured line intensities in the fluorescen ce excitation spectrum. Based on these data, a new assignment of the lines in the fluorescence excitation spectrum corresponding to totally symmetric modes 7 and 8 is suggested. (C) 2000 MAIK "Nauka/Interperiodica".