Quantum rotational dynamics of methane in MOF5

1
Quantum rotational dynamics of methane in MOF5
W. Zhou1,2 and T. Yildirim1,2
1University of Pennsylvania, 2NIST
DMR-0454672
ZnO4 cluster
CH4
Metal-organic framework (MOF) compounds are
nanoporous materials that show promise for
storage of gases such as H2 and CH4. Neutron
diffraction measurements and first-principles
calculations for CH4 molecules in MOF5 show that
3 of the 4 H atoms are relatively resistant to
thermal fluctuations. Using the CHRNS Disk
Chopper Spectrometer we have studied the quantum
rotational dynamics of CH4 molecules in MOF5 by
measuring rotational tunnel splittings . A
calculation using rotational potential barriers
of 41 and 22 meV around the 3- and 3'-fold axes
respectively is in good agreement with the
measurements and in reasonable agreement with the
results of total energy calculations using
density functional theory.
Tunnel splitting measurements at 4K are shown as
a line plot integrated over Q (black line), and
as an image plot, Q (Å-1) vs E (meV). The red
line plot represents the calculation.
W. Zhou and T. Yildirim, Phys. Rev. Lett. (in
preparation).