			15min:

LIFETIME BROADENING IN THE ROTATIONALLY RESOLVED ELECTRONIC SPECTRA OF SOME FURAN DERIVATIVES AND ANALOGS IN THE GAS PHASE \footnotemark[1] .

LEONARDO ALVAREZ-VALTIERRA AND DAVID W. PRATT, Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260; JOHN T. YI, Department of Chemistry, Winston Salem State University, Winston Salem, NC 27103.

Fluorescence lifetimes of the electronic origin and some higher vibronic bands of dibenzofuran (DBF) \footnotemark[1] and dibenzothiophene (DBT) have been determined from the analyses of their rotationally resolved S₁ leftarrow S₀ fluorescence excitation spectra in the gas phase. A decrease by a factor of eight in the fluorescence lifetime has been observed for DBT with respect to DBF, where presumably the heavy atom effect plays a significant role in the intersystem crossing mechanism of these heterocycles. The high resolution spectra of the electronic origin transitions of two non-concatenated furan derivatives, 2,5-diphenylfuran (DPF) and 2,5-diphenyl-1,3,4-oxadioxole (DPO), exhibit similar lifetime broadening, about four times greater than that of DBF. Detailed information about radiationless transitions in the "statistical" limit will be discussed.