Neutrons scattering techniques are ideally suited to directly probe H in materials due to the large incoherent scattering cross-section of hydrogen atom, and have been invaluable in providing direct insight into the local fluctuations and large amplitude motions in AB. Dihydrogen bonding may have a significant affect on materials to be used to store hydrogen for fuel-cell powered applications. We have noticed a trend of low temperature release of H2 in materials composed of hydridic and protonic hydrogen. This phenomenon has caught our attention and motivated our interest to gain more insight into dihydrogen bonding interactions in AB. We present results from a thorough Quasielastic Neutron Scattering (QENS) investigation of diffusive hydrogen motion in NH311BH3 and ND311BH3 to obtain (1) a direct measure of the rotational energy barriers the protonated species and (2) a confirmation of the 3-site jump model for rotational motion. The amplitude of the energy barrier of rotation of BH3 and NH3 determined by QENS are compared to those determined for BD3 and ND3 determined by 2H NMR studies.
Revised: July 21, 2008 |
Published: June 27, 2008
Citation
Hess N.J., M.R. Hartman, C. Brown, E. Mamontov, A.J. Karkamkar, D.J. Heldebrant, and L.L. Daemen, et al. 2008.Quasielastic neutron scattering of -NH3 and -BH3 rotational dynamics in orthorhombic ammonia borane.Chemical Physics Letters 459, no. 1-6:85-88.PNNL-SA-58774.doi:10.1016/j.cplett.2008.04.130