title: Rotational dynamics of methyl groups in m-xylene.
abstract: Methyl group dynamics of m-xylene was investigated by using incoherent inelastic and quasi-elastic neutron scattering. Inelastic measurements were carried out at the high flux backscattering spectrometer HFBS at the National Institute of Standards, quasi-elastic measurements at the time-of-flight spectrometer NEAT at the Hahn-Meitner-Institute. Rotational potentials are derived which describe the tunnel splittings, first librational, and activation energies of the two inequivalent CH(3) groups. Indications for coupling of the methyl rotation to low-energy phonons have been found. The finite width of one tunneling transition at He temperature is described by direct methyl-methyl coupling. The combined results of the experiments and the calculations allow a unique assignment of rotor excitations to crystallographic sites.
authors.affiliation: Bragg Institute, Australian Nuclear Science & Technology Organisation, Menai, NSW 2234, Australia. oki@ansto.gov.au
authors.forename: O
authors.initials: O
authors.lastname: Kirstein
authors.forename: M
authors.initials: M
authors.lastname: Prager
authors.forename: R M
authors.initials: RM
authors.lastname: Dimeo
authors.forename: A
authors.initials: A
authors.lastname: Desmedt