title: Hyperfine coupling in methyl radical isotopomers.
abstract: The hyperfine coupling constants (hfcs) of two methyl radical isotopomers, CH2Mu and CD2Mu, have been measured over a wide range of temperature in ketene and ketene-d2, from which the radicals were generated. The magnitudes of the hfcs of these muoniated methyl radical isotopomers are larger than those of CH3 and CD3 due to larger zero-point energy in the out-of-plane bending mode. In contrast to CH3 and CD3, where the coupling constants become smaller with increasing temperature, the negative hfcs of the muoniated radicals were found to increase in magnitude (become more negative) with temperature, passing through a maximum near the boiling point of ketene. This behavior is attributed to a solvent-induced change in the force constant of the out-of-plane bending mode. The opposite temperature effect known for CH3 and CD3 is explained by excitation of the low frequency out-of-plane bending mode. This effect is much smaller in the muoniated radicals, where the vibrational frequency is significantly higher due to the light mass of muonium; consequently, the solvent effect dominates at low temperatures.
authors.affiliation: Department of Chemistry and TRIUMF, Simon Fraser University, 8888 University Drive, Burnaby, B.C. V5A 1S6, Canada.
authors.forename: Iain
authors.initials: I
authors.lastname: McKenzie
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Brodovitch
authors.forename: Khashayar
authors.initials: K
authors.lastname: Ghandi
authors.forename: Brett M
authors.initials: BM
authors.lastname: McCollum
authors.forename: Paul W
authors.initials: PW
authors.lastname: Percival
mesh_terms: D000465:Algorithms; D003080:Cold Temperature; D003903:Deuterium / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005030:Ethylenes / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D007536:Isomerism; D007554:Isotopes / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D044366:Transition Temperature
chemical_list: D005030:Ethylenes; D005609:Free Radicals; D007554:Isotopes; D007659:Ketones; D012997:Solvents; C051224:methyl radical; D003903:Deuterium; C008223:ketene; D008697:Methane