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 (SO2F2)-S-34 and (SO2F2)-O-18 samples, the three absorptions at 1284.9, 1109.3, and 567.0 cm -l 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 (2)A(1) ground state with nonplanar C2, symmetry. Compared with the neutral SO(2)F(2)molecule, dramatic increases in the S-F bond length (0.295 angstrom) and F-S-F bond angle (41.0 degrees) 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.