SHIFT FROM AN INVERSE TO A NORMAL ISOTOPE EFFECT ON THE NONRADIATIVE DECAY-RATE OF ANTHRACENE-D(10) OBSERVED UNDER PARTIALLY JET-COOLED CONDITIONS

The absorption and fluorescence excitation spectra of anthracene-d(10) in the first excited singlet state were measured under partially jet- cooled conditions. From the ratio of the corresponding peak intensitie s of both spectra the fluorescence quantum yields were evaluated for a few sequence bands as well as single vibronic levels. In contrast to the case of anthracene-h(10), the values for the sequence bands (Phi(f ) = 0.17-0.24) exceed that of the 0(0)(0) band (Phi(f) = 0.13), sugges ting a resume of normal isotope effect on intersystem crossing. This n ovel finding is discussed in relation to the fluorescence Lifetimes of anthracene-d(10) measured in the gas phase. (C) 1998 Elsevier Science B.V. All rights reserved.