Ab initio calculation of spin–orbit interaction in polyatomic molecules using Gaussian-type wavefunctions

A set of programs has been developed to calculate molecular spin–orbit interaction with Gaussian-type wavefunctions in connection with the popular GAUSSIAN 76 program. The spin–orbit contributions to the fine structure of O₂ (X³∑_g^?), NH (X³∑^?), and CH₂ (X³B₁) are evaluated with the standard STO -3G and 6-31G basis sets; for NH the influence of bond functions added to the latter basis set is also investigated. The results are compared to values previously obtained with other types of basis sets.