PROTONATED THIOHYPOFLUOROUS ACID, FSH2- THEORETICALLY PREDICTED TO BESTABLE AND EXPERIMENTALLY OBSERVED IN THE GAS-PHASE( )

Protonated FSH has been theoretically investigated at the Gaussian-2 l evel of theory. The S-protonated isomer 1 was found to be more stable than the fluorine-protonated isomer 3 by 28.6 kcal mol(-1), and the pr oton affinity of FSH at the sulphur atom is computed as 162 kcal mol(- 1) at 298 K. The interconversion of the two ions occurs through the th ree-centre transition structure 6, less stable than 1 by 53 kcal mol(- 1). The experimental observation of gaseous FSH2+ ions, obtained from the ionization of a mixture of H2S and NF3, is fully consistent with t he theoretical prediction of at least one deep energy minimum on the p otential energy surface and corroborates and extends previous experime ntal evidence for stable H2SF+SbF6- salt in anhydrous HF at 195 K.