ISOTOPE-DEPENDENT QUENCHING OF SINGLET MOLECULAR-OXYGEN (1-DELTA-G) BY GROUND-STATE OXYGEN IN SEVERAL PERHALOGENATED SOLVENTS

The deactivation of O2(1-DELTA-g) by ground-state O2 was investigated by the direct time-resolved phosphorescence technique in four perhalogenated solvents at 295 K. A very strong isotope effect of k(Q)16/k(Q)18 = 70 was observed on the quenching rate constant, which is reproduced by the model developed by Maier, Wild, Klingshirn and Plotz for O2 (1-DELTA-g) deactivation in pure O2. Thus, solvent molecules do not support quenching by O2. k(Q)16 ranges from 2600 M-1 s-1 in perfluorohexane to 4100 M-1 s-1 in perfluorodecalin and is about three times larger than in gaseous O-16(2). The variation of k(Q)16 correlates with changes in the packing fraction of the solvents.