Abstract Structure, spectroscopic constants and molecular properties of selected diatomic anions in their ground states have been studied in detail using HF/DF B3LYP method. The consistency of the calculated values of spectroscopic constants and molecular properties has been tested using four basis sets with improved quality. The spectroscopic constants and molecular properties of these diatomic ions agree well with the experimental and theoretical values wherever available. Most of the spectroscopic constants and molecular properties of these ions, in particular the spectroscopic constants of SiO − , CS − and the molecular properties of SiN − , CP − , SiO − are first reported.