High-Resolution Fourier Transform and Diode–Laser Spectroscopy of the ν₆ Fundamental of C₂F₆ and Associated Hot Bands

Abstract

High-resolution infrared spectra of the ν₆ (713 cm⁻¹) band region of C₂F₆ vapor have been recorded at several temperatures. Spectra at 77, 200, and 300 K were recorded using a Fourier transform spectrometer with unapodized resolutions of 0.0018 cm⁻¹ (200 and 300 K) and 0.008 cm⁻¹ (77 K). Spectra with rotational temperatures in the range 5–50 K were recorded in a supersonic jet using diode–laser absorption spectroscopy. The ν₆ band contains two clear sequences of hot-bands: one arises from the ν₄ torsional vibration at 67.5 cm⁻¹; the other, shorter, weaker progression is built on the doubly degenerate ν₉ vibration at 220 cm⁻¹. They lie to high and low wavenumbers of the fundamental band, respectively. Eleven series were assigned and fitted to these hot bands. A perturbed series in the ν₄ sequence is considered, by analogy with the infrared spectrum of C₂H₆ vapor, to be caused by an xy–Coriolis interaction either between 5ν₄ and ν₉ + 2ν₄ in the ground state or, in the upper state, ν₆ + 5ν₄ with ν₆ + ν₉ + 2ν₄ or ν₆ + 5ν₄ with 2ν₈. One further series resolved only in the jet spectrum and lying very close to the fundamental is almost certainly due to the ν₆ fundamental of the isotopomer ¹³C¹²CF₆.