  Innermolecular motion in Na3AlH6 gives rise to a Lorentzian spectrum with a
wavenumber-independent width of about 1 micro-eV at 180 deg C, which is
probably due to rotation of AlH6 tetrahedra. There is no such quasielastic line
in NaAlH4 or NaH. Based on this finding, time-resolved measurements on the
neutron backscattering spectrometer SPHERES were used to monitor the
decomposition kinetics of sodium alanate, NaAlH4 to Na3AlH6 to NaH. Both
reaction steps were found to be accelerated by autocatalysis, most likely at
the surfaces of Na3AlH6 and NaH crystallites.
