A theoretical study of high electron affinity sulfur oxyfluorides:: SO3F, SO2F3, and SOF5

Gaussian-2 theory was used to study a series of sulfur oxyfluorides that have exceptionally high electron affinities (EAs). Optimized geometries were computed for SO3F, SO2F3, SOF5, and their corresponding anions at the MP2(full)/6-311+G(d) level of theory. Both SO3F and SOF5 are found to be stable with respect to dissociation, while SO2F3 is metastable with respect to SO2F2 + F. In all cases, electron attachment results in a shortening of one long SO bond within the molecule and a corresponding increase in the remaining SF and SO bonds; a significant portion of the excess charge is accommodated in an SO bonding orbital. Harmonic vibrational frequencies with IR and Raman intensities were computed for all species, and the calculated vibrational spectra of SOF5- and SO2F3- are compared to the reported experimental spectra. The EAs of SO3F, SO2F3, and SOF5 are found to be 5.53, 5.50, and 5.14 eV, respectively, all well exceeding the threshold of 3.6 eV that defines a superhalogen species. The corresponding anion vertical detachment energies and neutral vertical attachment energies are also reported here. The calculated EA of SO3F is discussed in relation to the gas-phase acidity of FSO3H. The homolytic bond dissociation energy of FSO3H is found to differ significantly from the previous estimate, suggesting the previous experimental estimate for the EA of SO3F [J. Am. Chem. Soc. 114 (1992) 4299] be revised upward from 4.8 to 5.2 eV. (Int J Mass Spectrom 218 (2002) 207-215) (C) 2002 Elsevier Science B.V. All rights reserved.