Structures and relative stabilities of bisulfite ion isomers

Abstract

The structure and equilibria of the bisulfite ion in the gas phase are investigated using ab initio electronic structure methodology. The structures analysed were the C 3v structure and the syn and anti tautomers of the C s structure. Optimized geometries and total energies were determined for a variety of basis sets and levels of theory. Polarization functions had profound effects on both geometries and relative energies. Addition of diffuse functions was found to affect significantly both relative stabilities and geometries at the MP2/3–21 + G ∗ level. However, diffuse functions had minor effects at the MP2/6–31 + G ∗ level. Inclusion of electron correlation via second-order (MP2) and full fourth-order (MP4SDTQ) Møller-Plesset perturbation treatments was found to have moderate effects on geometries and relative stabilities. Normal mode vibrational frequencies were calculated for all isomers studied. The lowest energy structure was found to be an asymmetric form of the syn conformation of the C s tautomer.