Infrared diode laser study of the hydrogen bifluoride anion: FHF− and FDF−

The ν3 vibration–rotation transition of the hydrogen bifluoride anion in the X̃ 1Σ+g state has been detected for the first time by infrared diode laser spectroscopy using the magnetic field modulation technique. The anion was generated by a hollow cathode discharge in a mixture of H2 and a fluorine-contained molecule such as CF4, C2F4, and CHF3. The carbon compound was indispensable to produce the anion. Identification of the species was based on the spectral pattern showing intensity alternation, the magnitude of the rotational constant (B″=0.334 181 cm−1), and the ion drift velocity sign determined by the velocity modulation method. The observed ν3 frequencies of FHF−(1848.699 cm−1) and FDF−(1397.236 cm−1) are much different from the reported values in the solid phase. By contrast, the ν1 and ν2 frequencies estimated from the centrifugal distortion constant and the perturbation of Coriolis interaction between the ν1+ν2 and ν3 states are in good agreement with solid state measurements.