Magnetic hyperfine coupling of a methyl group undergoing internal rotation: a case study of methyl formate

• Published in: The Journal of chemical physics Vol. 134; no. 7; p. 074314
• Main Authors: Tudorie, M, Coudert, L H, Huet, T R, Jegouso, D, Sedes, G
• Format: Journal Article
• Language: English
• Published: United States 21.02.2011
• ISSN: 1089-7690
• DOI: 10.1063/1.3554419

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.