title: Molecular structure and dynamics in the low temperature (orthorhombic) phase of NH3BH3.
abstract: Variable temperature 2H NMR experiments on the orthorhombic phase of selectively deuterated NH3BH3 spanning the static to fast exchange limits of the borane and amine motions are reported. New values of the electric field gradient (EFG) tensor parameters have been obtained from the static 2H spectra of V(zz) = 1.652 (+/-0.082) x 10(21) V/m(2) and eta = 0.00 +/- 0.05 for the borane hydrogens and V(zz) = 2.883 (+/-0.144) x 10(21) V/m(2) and eta = 0.00 +/- 0.05 for the amine hydrogens. The molecular symmetry inferred from the observation of equal EFG tensors for the three borane hydrogens and likewise for the three amine hydrogens is in sharp contrast with the C(s) symmetry derived from diffraction studies. The origin of the apparent discrepancy has been investigated using molecular dynamics methods in combination with electronic structure calculations of NMR parameters, bond lengths, and bond angles. The computation of parameters from a statistical ensemble rather than from a single set of atomic Cartesian coordinates gives values that are in close quantitative agreement with the 2H NMR electric field gradient tensor measurements and are more consistent with the molecular symmetry revealed by the NMR spectra.
authors.affiliation: Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, P. O. Box 999, Richland, Washington 99352, USA.
authors.forename: Herman
authors.initials: H
authors.lastname: Cho
authors.forename: Wendy J
authors.initials: WJ
authors.lastname: Shaw
authors.forename: Vencislav
authors.initials: V
authors.lastname: Parvanov
authors.forename: Gregory K
authors.initials: GK
authors.lastname: Schenter
authors.forename: Abhijeet
authors.initials: A
authors.lastname: Karkamkar
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Hess
authors.forename: Chris
authors.initials: C
authors.lastname: Mundy
authors.forename: Shawn
authors.initials: S
authors.lastname: Kathmann
authors.forename: Jesse
authors.initials: J
authors.lastname: Sears
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Lipton
authors.forename: Paul D
authors.initials: PD
authors.lastname: Ellis
authors.forename: S Thomas
authors.initials: ST
authors.lastname: Autrey