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Struktur und Dynamik Poster: Mi., 14:00–16:30 M-P150
Methyl rotational potentials and guest molecule dynamics in water clathrates
of methyl halides
Michael Prager 1 , Jürgen Allgaier 1 , Werner Press 2 , Arnaud Desmedt 3 ,
Alexandra Buchsteiner 4 , Margarita Russina 4 , Jörg Pieper 4 , John Tse 5 , Denis
Klug 5 , Marie Plazanet 6
1 IFF, Forschungszentrum Jülich, 52425 Jülich, Germany
– 2 Inst. für Experimentalphysik, Universität Kiel, Germany
– 3 LPCM, Universite de Bordeaux 1, France
– 4 Hahn-Meitner Institut, Berlin, Germany
– 5 Steacie Institute of Molecular Science, NRC of Canada, Ontario, Canada
– 6 Institut Laue-Langevin, Grenoble, France
The CH3X water clathrates, X=F,Cl,Br, assume the cubic I structure of clathrates as
the natural methane clathrate [1]. The interaction with the cage is significantly different
to the methane case due to the presence of a dipole moment and a tendency to
form hydrogen bonds. By changing the guest molecule these properties can be changed
and allow new insight on the guest-host interaction. Such tuning of the interaction is
not possible with the symmetric methane molecule. The clathrate structure with CH3I
guest molecules is cubic II. Rotational potentials of methyl groups were obtained from
high resolution neutron tunneling spectroscopy. They give information on the potential
energy surface of the cage with e.g. different adsorption sites and on disorder of the
hydrogen bond network of the cage. Quasielastic spectra allow to study in addition to
methyl rotation the rotational and translational dynamics, often called rattling, of the
whole molecule in the cage. Beside of the published results on CH3I [2] and CH3F [3]
clathrates we will present new results on the chlorine and bromine compounds.
[1] C. Gutt et al, J. Chem. Phys. 113,4713(2000)
[2] M. Prager et al, J. Phys.: Condens. Matter 16,7045(2004)
[3] M. Prager et al, Phys. Chem. Chem. Phys. 7,1228(2005)