Dynamics of methane trapped in C{sub 60} interstices

Journal Article · Sat Jul 01 04:00:00 EDT 2000 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.481797· OSTI ID:20216848

Kwei, George H ^[1]; Trouw, Frans ^[2]; Morosin, Bruno ^[3]; King, Harry F ^[4]

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1. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2. Argonne National Laboratory, Argonne, Illinois 60636 (United States)
3. Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
4. Department of Chemistry, State University of New York, Buffalo, New York 14260 (United States)

We have carried out inelastic neutron scattering studies of the methane/C{sub 60} system in order to understand the hindered rotational and vibrational dynamics of methane trapped in C{sub 60} interstices and to determine the structure around the interstitial site. At temperatures of 20 K and below, we observe inelastic peaks from rotational transitions of the CH{sub 4}. These transitions allow unambiguous assignment of the hindered rotational energy levels and a determination of the interaction potential. The appearance of two peaks for one of the J=0{yields}3 transitions implies the existence of two distinct kinds of interstitial sites and the measured transition energies suggest rotational barriers of about 26 and 16 meV for these sites. Time-dependent changes in peak heights indicate slow (t{sub 1/2}{approx_equal}2.6 h) triplet{yields}quintet nuclear spin conversion that necessarily accompanies the J=1{yields}0 rotational relaxation. We also have observed an inelastic peak at 10.9 meV in a region where there is a gap in the calculated, and otherwise dense, rotational spectrum. We believe that this must correspond to a local vibrational mode of CH{sub 4} rattling in its cage at {approx}2.6 THz. Other peaks involving higher-energy vibrational excitations in CD{sub 4}/C{sub 60} correspond in energy to assigned peaks in the inelastic neutron scattering spectra of C{sub 60}, albeit sometimes with different intensities. Taken together, these findings suggest the rotation of CH{sub 4} is hindered by the C{sub 60} cage and that the vibrations of CH{sub 4} and C{sub 60} are loosely coupled. (c) 2000 American Institute of Physics.

• OSTI ID: 20216848
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 1 Vol. 113; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CONFORMATIONAL CHANGES
EXPERIMENTAL DATA
FULLERENES
INELASTIC SCATTERING
INTERSTITIALS
METHANE
NEUTRON DIFFRACTION
ROTATIONAL STATES
TRAPPING
VIBRATIONAL STATES