Trapped H$_{2}$ in AlH$_{3}$

Trapped molecular hydrogen has been discussed for years in H-storage systems such as NaAlH$_{4}$. Here we report proton NMR and neutron vibration spectroscopy (NVS) evidence for H$_{2}$ in AlH$_{3}$ samples. In static sample NMR, a sharp line appears on top of the broad AlH$_{3}$ solid signal. MAS further sharpens this line and identifies it as H$_{2}$ by its chemical shift. Upon cooling, the line broadens and disappears near 20K, confirming the H$_{2}$ identification. NVS reports energy-gain peaks at the H$_{2}$ rotational energy (J=1 to 0).