Knowledge Bank

The first excited singlet state absorption system of $SO2$ is interpreted as arising predominantly from massive vibronic coupling between a zero order, narrow, Franck-Condon allowed $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$B$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ state and the vibronic levels of a forbidden $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$A$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ state. Calculations based on the Langhoff-Robinson-$Berg1,2$ model using reasonable assumptions about the nature and number of the $A2$ vibronic states shows the interaction matrix element averages out at roughly 900 $cm-1$ for each significantly interacting state. Single vibronic fluorescence spectra are shown to support the application of this model to $SO2$.