			15min:

THE LOW-LYING STATES OF SF_n SPECIES (n=1--6): INSIGHTS INTO HYPERVALENCY FROM THE RECOUPLED PAIR BONDING MODEL.

D. E. WOON AND T. H. DUNNING JR., Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801.

High level MRCI and RCCSD(T) calculations with correlation consistent basis sets were used to characterize SF_n species. By examining both the stable structures and the bonding processes that occur during SF_n + F rightarrow SF_n+1 additions, we have derived a new model for describing hypervalent behavior that we call recoupled pair bonding, in which a pair of electrons on S can be decoupled to allow formation of a bond with F. The new model accounts for the origin of hypervalency, the presence of low-lying excited states, and the structures and spectral properties of neutral and ionic SF_n species; it has more predictive capability than other models. For example, while SF and SF₂ both have covalently bonded ground states, they each have low-lying excited states with at least one recoupled pair bond. To the best of our knowledge, the SF(⁴ Sigma ^-), SF₂(³B₁), and SF₂(³A₂) states have not yet been observed experimentally.