Knowledge Bank

The lifetime of the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}B1$ state of $SO2$ has been measured as a function of pressure and extrapolated to zero pressure. The results are in fair agreement with those of Collier et $al.1$ For comparison, the radiative lifetime has been calculated from the absorption and emission spectra using the formula of Strickler and $Berg.2$ The absorption spectrum was measured using a Cary Model 17 spectrophotometer. Integration of the absorption intensity over the whole band is not possible because it is superimposed on another transition. For this reason, Franck-Condon factors were calculated for the vibronic bands which could be assigned. The integrated intensity of these bands was measured, and the Franck-Condon factors used to extrapolate the intensity over the entire electronic transition. Comparison of the calculated and observed lifetimes indicates that only 2% of the molecules reaching the triplet state emit; the rest undergo some nonradiative process.