Spin-orbit interaction in polyatomic molecules: Ab initio computations with Gaussian orbitals

Standard sets of Gaussian atomic orbitals (STO -3G , STO -4.31G ) are used to evaluate spin-orbit coupling constants in linear molecules (CO, NNN) and spin-orbit effects on singlet–triplet transition intensities in formaldehyde. All spin-other orbit effects have been included. In all cases spin-other orbit interactions form a large fraction of the matrix elements. Simple formulae to evaluate spin-orbit one- and two-electron integrals over atomic orbitals are presented. Standard molecular integral programs can be used for the computation of spin-orbit integrals.