Ab initio computations of spin‐orbit interactions in polyatomic molecules. Splitting of sulfur L II , III states and singlet–triplet transitions in SO2

Spin‐orbit interactions among the ground and the first few excited electronic states of SO2, are computed with ab initio molecular wave functions and Gaussian atomic orbitals. All spin‐other orbits contributions to the matrix elements are included. The computed intensity of the first singlet–triplet transition is found to be in broad agreement with experiment and sensitive to an extension of the configuration interaction expansion of molecular wave functions. Also, the splitting of sulfur LII,III states in SO2 is derived as an example of large spin‐orbit interactions among electronic states.