Fluorescence and nonradiative processes of dioxin vapors

•Fluorescence, excitation and sensitized-excitation spectra of 5 dioxins vapors were measured.•These are dibenzofuran, chlirodibenzofuran, dichlorodibenzofuran, dibenzo-p-dioxin and chlorodibenzo-p-dioxin.•Nonradiative rates of dibenzodioxins increase with increasing excitation energy, but those of dibenzofurans are unchanged.•Main nonradiative process from S1 of dibenzofurans is intersystem crossing to T1 and internal conversion to S0.•Main nonradiative process from S1 of dibenzo-p-dioxins is internal conversion to S0.

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.

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