Infrared Spectra of the SO₂F₂^- Anion in Solid Argon and Neon

Sulfonyl fluoride anion (SO₂F₂^-) was produced during codeposition of laser-ablated metal atoms, ions, and electrons with SO₂F₂ in argon and neon matrixes at 4 K. The structure of SO₂F₂^- was determined by infrared spectroscopy and density functional theory calculations. On the basis of the experiments using ³⁴SO₂F₂ and S¹⁸O₂F₂ samples, the three absorptions at 1284.9, 1109.3, and 567.0 cm^-1 in argon and 1289.0, 1116.2, and 576.8 cm^-1 in neon were assigned to the antisymmetric and symmetric O-S-O stretching and SO₂ wagging modes of SO₂F₂^-, respectively. These assignments were further supported by frequency and isotopic frequency ratio calculations. The SO₂F₂^- anion possesses a ²A₁ ground state with nonplanar C_{2 v} symmetry. Compared with the neutral SO₂F₂ molecule, dramatic increases in the S-F bond length (0.295 Å) and F-S-F bond angle (41.0°) were found for the anion, which result from the S-F antibonding character of the singly occupied molecular orbital. The SO₂F₂^- anion was formed via electron capture by SO₂F₂ in the gas phase before being deposited into the cryogenic matrix. The matrix environment stabilized this anion, but it was destroyed by UV-vis irradiation and presumably converted to the neutral SO₂F₂ molecule.