The fluorosulfate radical Structural theory and assignment of electronic absorption systems

In the vapor phase, the fluorosulfate radical SO3F• exists in equilibrium with its dimer, peroxydisulfuryl difluoride. The absorption spectrum of the mixture has been studied under both low and high resolution, and absorption temperature-dependence studies show that three systems can be ascribed to the radical. These consist of two weak diffuse systems in the 14000-13000 Å and 8400-7200 Å regions, and a stronger discrete system with origin at 5160 Å. Two types of CNDO calculations on the lower electronic states of the radical have been performed. Of these, the “open-shell” calculation in particular suggests that the three transitions involved are, in order of increasing energy, 2A1 - X̃2A2, 2E(1) - X̃2A2 and 2E(2) - X̃2A2. The electronic promotion involved is confined mainly to the locality of the oxygen atoms. It is shown that these assignments agree with the observed spectra, with a considerable geometrical change occurring on excitation in the transition at lowest energy. The theory of Jahn-Teller interactions is developed to include spin-orbit interactions, since both of these types can occur in a 2E state of the radical.