Di-hydrogen in cation-substituted zeolite-X - an inelastic neutron scattering study

An inelastic neutron scattering (INS) study of the rotational–vibrational spectrum of dihydrogen sorbed by zeolite X having substituted sodium, calcium and zinc cations is reported. The rotational–vibrational spectrum of H2 was observed at low energy transfer (below ca. 25 meV, 202 cm21); the vibration was that of the H2 molecule against the binding site (H2–X, not H–H). The vibration frequency was proportional to the polarising power of the cation (Na+ , Ca2+ , Zn2+). Polarisation of the H2 molecule dominated the interaction of H2 with this binding site. The total scattering intensity was proportional to the dihydrogen dose. However the vibrational intensities became constant at ca. 0.3 wt% showing that the H2 binding sites had saturated. Additional dihydrogen appeared as unbound or weakly bound dihydrogen exhibiting recoil