1. The following programs were used in this work: MELD, HF and CI: McMurchie, L.E., Elbert, S.T., Langhoff, S.R., and Davidson, E.R.
2. MOLPRO, HF: Meyer, W., and Werner, H.-J.
3. MCSCF: Werner, H.-J., and Knowles, P.J., 1985, J. Chew. Phys. 82:5053
4. Knowles, P.J., and Werner, H.-J., 1988, Chem. Phys. Letters
115:259
5. CI: Werner, H.-J., and Knowles, P.J., 1988, J. Chem. Phys. 89:5803