Abstract

Relaxation and quenching of excited states of Br2 in CC14 is studied by time-resolved photothermal grating combined with near-IR fluorescence. A slow rise in diffraction transient signals from photothermal gratings, due to nonradiative relaxation of excited states, is observed for Br2 in CC14. Near-IR fluorescence measurement reveals that there are two decay components; the fast component has a lifetime about 6 ns, and the slower component has a lifetime around 20 ns, depending on Br2 concentration and oxygen content in the sample. The slower component is assigned to the decay of A' state. From the amplitudes of thermal grating, the quantum yield of the A' state formation is estimated to be 0.33+0.03. Stern-Volmer plot of the measured decay rate of A' state, including results obtained from both near-IR fluorescence and photothermal grating measurement, suggests that quenching of A' state proceeds initially at diffusion-limited rate at low concentration and reduces to nondiffusion-limited at higher concentration. Possible mechanisms for the observed decrease of quenching rate as concentration increases are also discussed.

© 1992 Optical Society of America