First line intensities of the ν3+ν6 band of methyl fluoride

Abstract

Infrared spectra of CH${}_3$F were recorded in the 2200 cm⁻¹ region using a Fourier transform spectrometer in Reims, France, with a resolution of 0.003 cm⁻¹. The measurements were conducted using spectra recorded using a White-type cell (set to an absorption path length equal to 8.26 m) and different pressures of CH${}_3$F (1–15 mbar). This spectral region corresponds to the ${\nu }_3+{\nu }_6$ band, which is measured for the first time in this work. Experimental line positions and intensities were determined using the Voigt lineshape together with a single-spectrum fitting procedure. The band assignment was carried out up to $J=45$ and $K=15$ using our home-made SpectraMatcher computer code, resulting in more than 1800 measured lines. Strong intensity perturbations were observed, explained by a strong Coriolis coupling between the upper states of the $2{\nu }_3$ and ${\nu }_3+{\nu }_6$ bands. The squared dipole moment was determined for each transition, resulting in the determination of the vibrational transition moment and the Herman–Wallis coefficients of the ${\nu }_3+{\nu }_6$ band using the Watson’s model.