Lasitha Senadheera

Molecular H2 trapped in AlH3 solid
Lasitha Senadheera, Erik M. Carla, Timothy M. Ivancic, Mark S. Conradi, R.C. Bowman Jr., S.-J. Hwang, Terrence J. Udovic. J. Alloy. Compd.. 2008; 463 (1-2): 1
Solid aluminum hydride, AlH3, has been proposed and studied for applications in hydrogen storage. In some samples, a comparatively narrow feature in the proton NMR spectrum is observed; we demonstrate here that this peak is due to molecular hydrogen (H2) trapped within the solid, presumably from earlier processing procedures or partial decomposition. Static and magic-angle spinning NMR show that the responsible species is highly mobile, even at 11 K. Neutron-energy-gain spectra obtained at 3.5 K yield a feature at or near the free-rotor H2 energy difference between the J = 1 and J = 0 states. Both NMR and neutron scattering demonstrate ortho–para conversion at low temperatures. Similar NMR signatures in other hydrogen-storage solids such as NaAlH4 may also be due to trapped H2.