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

Abstract

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.