EFFECTS OF CLUSTERING OF RARE-GAS ATOMS ON THE RATE OF S-1-T-2 INTERSYSTEM CROSSING FOR 9-METHYLANTHRACENE

Laser induced fluorescence excitation spectra for 9-methylanthracene ( MEA) in a supersonic free jet were measured as a function of the stagn ation pressure of Ar, Kr and Xe, used as carrier gas. The 0-0 excitati on bands for complexes of type MEA Ar, were observed successively corr esponding to an increase in coordination number n with increasing stag nation pressure. On the other hand, excitation bands associated with s mall cluster; of Kr and Xe were scarcely observed, although strong exc itation bands associated with larger clusters were observed at largely red-shifted wavelengths. These observations combined with the measure ment of fluorescence lifetimes were interpreted in terms of two effect s of the clustering of rare-gas atoms on the intersystem crossing rate ; energy shift of S-1 relative to T-2 and heavy atom effect.