Effects of oxygen-18 substitution upon electronic relaxation in the 3B1 state of SO2

Abstract

We have measured phosphorescence lifetimes and quantum yields of solid S16O2 and S18O2 at several temperatures. Isotopic substitution was found to increase the phosphorescence lifetime of the 3B1 state of solid SO2 at 77 °K from 1.0±0.1 msec to 1.3±0.1 msec, and at 4.2 °K from 8.7±0.1 msec to 9.7±0.4 msec. The quantum yield of solid SO2 at 77 °K was determined to be 0.09±0.01 and at 4.2 °K was determined to be no less than 0.6±0.1. Radiative and nonradiative rate constants for 3B1 → 1A1 relaxation were calculated from our quantum yield and phosphorescence lifetime data. The nonradiative relaxation rate constant was found to be temperature dependent as well as isotope dependent, decreasing by a factor of 20 between 77 and 4.2 °K. At 1.4 °K, where the spin-lattice-relaxation rate is considerably reduced, three lifetime components could be resolved, and the phosphorescence decay time for the dominant spin state τ1 was found to be longer for S18O2 than for S16O2, consistent with our observations at higher temperatures.