FTIR spectra of the HF−2 and H2F−3 anions isolated in solid argon and neon

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Abstract
Argon diluted samples of HF were bombarded by low energy electrons (150–400 eV) from a thermionic electron source during condensation at 12 K. Several polyfluoride anions, which have extremely strong hydrogen bonds, were characterized using matrix infrared spectroscopy. Three principal ions were trapped in the argon matrix: HF−2 (1377 cm−1), H2F−3 (1815 cm−1), and ArnH+ (904 cm−1). Electron impact experiments performed with HF/DF mixtures gave counterpart absorptions: DF−2 (965 cm−1), HDF−3 (1707 cm−1), D2F−3 (1391 cm−1), and Arn D+ (644 cm−1). The 1377 cm−1 matrix band is assigned to ν3 of linear, centrosymmetric HF−2, based on agreement with solid state and matrix ion pair spectra, and ab initio calculations, and a proper H/D ratio (1.427) for a linear centrosymmetric species. However, this assignment challenges the recent 1848 cm−1 gas phase assignment to ν3 of HF−2 using laser spectroscopy; the 1848 cm−1 absorption exhibits an H/D ratio (1.323) that is too low for the ν3 vibration of centrosymmetric HF−2, and it should be reassigned to the ν1+ν3 combination band. The 1815 cm−1 matrix band is assigned to the out-of-phase H–F stretching fundamental of C2vH2F−3, which is in agreement with solid K+H2F−3 spectra.