Ab initioMO calculations of structures and electronic states of SF₆and SF₆⁻

Geometrical and electronic structures of SF 6 and SF 6 - have been determined using ab initio molecular orbital calculations in order to shed light on the mechanism of electron capture of SF 6 . The calculations (MP2/6-311G(d) + sp and MP2/6-311 + G(d) levels) showed that both SF 6 and SF 6 - have O h symmetry, while the S-F bond of SF 6 - is about 10% longer than that of SF 6 , indicating that the structure of SF 6 is deformed along the S-F symmetric stretching mode by accepting an excess electron. The calculations showed that the adiabatic electron affinities of SF 6 are positive (0.49-1.39 eV), which is in reasonable agreement with the experimental values (0.32-1.49 eV). The potential energy curve calculated as a function of an S-F bond of SF 6 - showed that SF 6 - is bound with respect to its dissociation limit (SF 5 - + F). The mechanism of electron capture of SF 6 is discussed on the basis of the theoretical results.