title: Magnetic hyperfine coupling of a methyl group undergoing internal rotation: a case study of methyl formate.
abstract: The hyperfine structure of methyl formate was recorded in the 2-20 GHz range. A molecular beam coupled to a Fourier transform microwave spectrometer having an instrumental resolution of 0.46 kHz and limited by a Doppler width of a few kHz was used. A-type lines were found split by the magnetic hyperfine coupling while no splittings were observed for E-type lines. Symmetry considerations were used to account for the internal rotation of the methyl top and to derive effective hyperfine coupling Hamiltonians. Neglecting the spin-rotation magnetic coupling, the vanishing splittings of the E-type lines could be understood and analyses of the hyperfine patterns of the A-type lines were performed. The results are consistent with a hyperfine structure dominated by the magnetic spin-spin coupling due to the three hydrogen atoms of the methyl group.
authors.affiliation: Laboratoire de Physique des Lasers, Atomes et Molécules, UMR 8523 CNRS-Université Lille 1, Villeneuve d'Ascq, France.
authors.forename: M
authors.initials: M
authors.lastname: Tudorie
authors.forename: L H
authors.initials: LH
authors.lastname: Coudert
authors.forename: T R
authors.initials: TR
authors.lastname: Huet
authors.forename: D
authors.initials: D
authors.lastname: Jegouso
authors.forename: G
authors.initials: G
authors.lastname: Sedes