Proton NMR studies of lanthanum nickel hydride: Structure and diffusion

The proton magnetic resonance spectrum of lanthanum nickel hydride LaNi _5.3H ₆ was measured over the temperature range 118°K < T < 300°K. The second moment of the absorption at 118°K is M₂ = 13.4 ± 0.3 G ². Several possible arrangements of the hydrogen atoms are discussed. Narrowing of the line above 140°K is analyzed in terms of proton diffusion and gives an activation enthalpy E = 21 ± 1 kJ mol ^-1, NMR correlation time pre-exponential 0.2 ps < τ_c⁰ < 1.6 ps and a self diffusion coefficient at 300°K of 2 × 10 ^-12 m ² s ^-1 < D < 2 × 10 ^-11 m ² s ^-1.