Reaction quantum yields, PCBs

Table II. Extinction Coefficients and Reaction Quantum Yields for PCB ...

PCB generally exhibit low fluorescence quantum yields (22), but phosphoresce efficiently ( jL) due to high Intersystem crossing yields from the singlet to the triplet excited states. Dechlorination of the rneta- and para- Isomers may Involve exclmer formation (29). In condensed PCB films the major photoprocesses probably Include e transfer reactions leading to both dechlorination and polymerization. 

Direct photolysis is a minor pathway for most congeners because of the poor overlap between PCB (Ar - Cl) absorption and the tropospheric solar spectrum. Following excitation, cleavage of the C — Cl bond can occur, hut the quantum yield is often low the aryl radicals thus formed suffer immediate oxidation hy atmospheric oxygen (reaction (1))... 

Considerable interest has been shown in this reaction as a possible technology for destruction of commercial PCBs. The photolysis of Aroclor 1254 in alkaline 2-propanol at 254 nm had a dechlorination quantum yield of 35, supporting a free-radical chain mechanism/ Studies elucidating the photodechlorination pathways of 3,3, 4,4, 5,5 -hexachlorobiphenyl, 3,3, 4,4 -tetrachlorobiphenyl, and related lower chlorinated PCB congeners in alkaline 2-propanol reveal that ... 

---