Rotational Tunneling in CH4 II: disorder effects

Press, W.; Prager, M.; Zamponi, M.; Krasnow, I.

doi:10.1063/1.3664726

Journal Article

PreJuSER-18724

Rotational Tunneling in CH4 II: disorder effects

Press, W. ; Krasnow, I. ; Zamponi, M.FZJ* ; Prager, M.FZJ*

2011
American Institute of Physics Melville, NY

The journal of chemical physics 135, 224509 (2011) [10.1063/1.3664726]

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Please use a persistent id in citations: http://hdl.handle.net/2128/7370 doi:10.1063/1.3664726

Abstract: Transitions within the tunneling multiplet of CH(4) in phase II have been measured in an experiment at the backscattering instrument BASIS of the Neutron Source SNS. They all involve transitions from or to T-states. A statistical model is put forward which accounts for local departures from tetrahedral symmetry at the sites of ordered molecules. Different from previous work, in which discrete sets of overlap matrix elements have been studied, now large numbers of elements as well as the ensemble of T-states are considered. The observed neutron spectra can be explained rather well, all based on the pocket state formalism of A. Hüller [Phys. Rev. B 16, 1844 (1977)]. A completely new result is the observation and simulation of transitions between T-states, which give rise to a double peaked feature close to the elastic position and which reflect the disorder in the system. CH(2)D(2) molecules in the CH(4) matrix are largely responsible for the disorder and an interesting topic for their own sake. The simple model presented may lend itself to a broader application.

Keyword(s): Basic research (1st) ; Others (1st) ; Chemistry (2nd) ; J

Classification:

Physics, Atomic, Molecular & Chemical

Note: A portion of this research at Oak Ridge National Laboratory's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U. S. Department of Energy. Also in the name of M.P., W.P. wishes to thank the Oak Ridge National Laboratory and the members of the BASIS team for the warm welcome and support. One of us (WP) is thankful to the Institut fur Experimentelle und Angewandte Physik at the University of Kiel for financial support of the measurement at SNS. We would like to thank A. Heidemann and K. Maki for helpful discussions and comments.

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