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.