Fluorescence and nonradiative processes of dioxin vapors

Fluorescence, fluorescence excitation, biacetyl-sensitized phosphorescence excitation and absorption spectra of five dioxins (dibenzofuran, 2-chlirodibenzofuran, 2,8-dichlorodibenzofuran, dibenzo-p-dioxin and 2-chlorodibenzo-p-dioxin) have been measured in the vapor phase. The intersystem crossing yields of dioxin vapors have been determined by means of a biacetyl sensitized phosphorescence method. It is shown that the nonradiative rates from the S1 state of dibenzo-p-dioxins increase significantly with increasing excitation energy, while those of dibenzofurans are almost unchanged. It is also shown that the main nonradiative process from S1 for dibenzofurans is both the intersystem crossing to T1 and internal conversion to S0 which includes possible photodecomposition, while that for dibenzo-p-dioxins is the internal conversion to S0, which also may include possible photochemical decomposition processes.