Deuteron Magnetic Resonance of Polycrystalline Deuteroammonia

Abstract

4600L. C. HOSKINS Ref. 2J. The actual computations were carried out by using an iteration procedure written for the IBM 1620 computer. The error limits in the force constants were set by arbitrarily admitting an error of ±0.4 cm-l in the P-R separations.The differences between the force constants of this work and those of Levin and Abramowitz are not solely due to interpolation errors and choices of structural parameters. Because of deviations of the theoretical and observed sum rules, the latter authors chose their force field as midway between that which reproduced .\3 and that which reproduced '\4, with the uncertainties in the force constants being set by estimated errors in the zeta values. In this work the force field was chosen as that which reproduced .\4 exactly, .\3 being set by the sum rule.The interaction force constants F34 for these Group V triflourides are clearly negative, being smallest for NF3 and approximately equal for PF 3 and AsF 3 . The bending force constant F44 decreases from NF3 to AsF3, but the F33 constant is largest for PFa and smallest for NFa.Besides the work by Levin and Abramowitz 3 and Hoskins and Lord,2 the only other attempt which has been made to determine the interaction constants of Group V trifluorides was made by Mirri et al. 16 using rotational distortion constants of PF3. Their value of F 34 = -0.677 mdyn is not consistent with the results using Coriolis coupling data, and an interaction force constant of this magnitude cannot result from uncertainties in the zetas. Their force constants for PFa are therefore probably in error.Deuterium magnetic resonance spectra of polycrystalline NDa have been observed at 75°, 159°, and 185°K. The measured values of e'qQlh were IS6±7 kc/sec at 75°K, and 72.5±0.9 kclsec at 159° and 185°K. The decrease at the higher temperatures has been attributed to rotational averaging. Single-crystal growth in the polycrystalline matrix was noted at the higher temperatures; it did not seriously interfere with the measurement of e 2 qQlh. Proton second-moment measurements were made on a polycrystalline sample of NHa at 75°K. The moment obtained was intermediate between the moments expected for the cases of fast and slow Ca reorientation. The rotational-transition temperature has been estimated to be 72°±2°K. A lower limit of 1.75 kcal/mole for the reorientational activation energy was estimated. An anomalous absorption peak was recorded in the center of the NDa spectrum at 75°K. It may possibly be ascribed to a double-quantum transition.

Expanded Close-Packed Fullerides: The Reactivity of Na2C60 with Ammonia

“…It is important to note that variable-temperature powder neutron diffraction shows that the space group symmetry is unchanged at this temperature. This is consistent with the molecule undergoing a reorientation about its C 3 axis with a frequency of greater than 10 8 Hz, and an effectively undistorted ammonia geometry (Δν is 72.5 ± 0.9 kHz in solid ND 3 between 159 and 185 K, and 71.6 ± 0.5 kHz in the Ag(ND 3 ) 2 + complex at 300 K 25 ). At 300 K, a heterogeneity in the characteristic times for reorientation of the ammonia molecules can be observed, with a sharp central peak suggestive of isotropic reorientation of the ammonia molecules.…”

Dynamics of Glass Forming Ammonia Hydrates

“…The azimuthal angle ϕ is defined as usual. Furthermore, δ Q denotes the effective anisotropy parameter which is a measure of the quadrupolar coupling constant. , To probe the molecular motion directly, stimulated-echo spectroscopy was performed and yielded the ensemble averaged (⟨...⟩) two-time correlation function F 2 false( t p .1em , t normalm false) = false⟨ cos [ ω Q false( 0 false) t p ] .25em cos [ ω Q false( t normalm false) t p ] false⟩ , which depends on the mixing time t m and on the evolution time t p . As an experimentally adjustable parameter, the latter allows one to set the geometrical sensitivity of the experiment.…”

Translational and Rotational Dynamics of Molecules Confined in Zeolite Nanocages by Means of Deuteron NMR

“…The quadrupole constant for ND 3 was estimated to be 217.5 kHz, or in the range of 221.1–239.1 kHz . We take 228 kHz as a common value on the basis of our study of spectra at low temperature.…”