First Line Intensities of the Ν3+Ν6 Band of Methyl Fluoride

Abstract

Infrared spectra of CH3F were recorded in the 2200 cm−1 region using a Fourier trans-form spectrometer in Reims, France, with a resolution of 0.003 cm−1. The measurementswere conducted using a White-type cell with a pathlength of 8.26 m at different pressuresof CH3F between 1 and 15 mbar. This spectral region corresponds to the ν3 + ν6 band,which is measured for the first time in this work. Experimental line positions and intensi-ties were determined using the Voigt lineshape as a model in mono-spectrum fitting. Theband assignment was carried out up to J = 45 and K = 15 using our home-made Spec-traMatcher computer code, resulting in more than 1800 measured lines. Strong intensityperturbations were observed, explained by a strong Coriolis coupling for 2ν3 and ν3 + ν6bands. The squared dipole moment was determined for each transition, resulting in thedetermination of the vibrational transition moment and the Herman–Wallis coefficients ofthe ν3 + ν6 band using the Watson’s model.

Keywords: Methyl fluoride, High-resolution spectroscopy, Fourier transform spectroscopy, Line-by-line intensity.