Quasielastic neutron scattering of –NH3 and –BH3 rotational dynamics in orthorhombic ammonia borane

Abstract: Energy barriers for rotation of –NH3 and –BH3 in the orthorhombic phase of ammonia borane, NH3BH3, were determined using quasielastic neutron scattering (QENS). QENS confirms the 3-site jump model of rotational diffusion and yields barrier heights of 23.6±1.0kJ/mol and 14.8±0.4kJ/mol for the borane and amine groups, respectively, which are comparable to barrier heights determined by recent 2H and 15N NMR studies suggesting no significant isotope effect on rotational motion in the orthorhombic phase of ammonia borane. [Copyright &y& Elsevier]