1 Centre for Research in Molecular Modeling and Department of Chemistry & Biochemistry, Concordia University, Montréal, Québec H4B 1R6, Canada.

High-level ab initio calculations employing the multireference configuration interaction and coupled clusters methods with a correlation-consistent sequence of basis sets have been used to obtain accurate potential energy curves for the complex of the sodium cation with the iodine atom. Potential curves for the first two electronic Lambda-S states have very different characters: the potential for the 2pi state has a well depth of approximately 10 kcal/mol, while the 2sigma state is essentially...