th  - 1988 - 51st ENC Conference

102
] STRONG 181Ta OUADRUPOLE INTERACTIONS DETECTED VIA CROSS-RELAXATION
TO HYDROGEN BY PROTON SPIN-LATTICE RELAXATION RATE STUDY IN TAB.322 : D.R.
Torgeson*, J-W. Han and R.G. Barnes, Ames Laboratory + and Department of
Physics, Iowa State University, Ames, Iowa 50011
Proton spin-lattice relaxation rate R 1 measurements of hydrogen in the
Ta2H metallic hydride phase of TaH 0 322 at 130 K have been made as a function
of proton magnetic resonance frequencies from 24 to 105 MHz. Contributions to
the proton Rl.arise from conduction elegl[ons, long-range diffusion (at higher
temperatures) i an~ cross-relaxation by ISITa spins.
The measured H relaxation rates R 1 show a strong, extremely broad (35 MHz
wide) peak or collection R~ peaks centered at 70 MHz that we attribute to
cross-relaxation by the 1°iTa spins which are themselves strongly relaxed by
conduction electrons and quadrupole interactions.
Interpretation of these resplls is complicated by the increasing strength
of the Zeeman splitting of the ~SITa nuclear electric quadrupole energy levels
that results from the stepped increase in the external magnetic field
necessary for the proton R 1 measurements from 24 to 105 MHz. From these
"spectra", we estimate the 181Ta pure quadrupole frequency ~0 to be - 40 MHz
and the electric field gradient (EFG) asymmetry parameter-~-- 0.5.
The orthorhombic crystal structure of Ta2H and the hydrogen occupation of
alternate planes of tetrahedral interstitial sites within the structure
indicate the crystalline EFG to have an asymmetry parameter ~ ~ 0.6. A more
detailed interpretation of the results will be given, as well as a description
of the experimental procedures employed to complete these measurements.
+Operated for the USDOE by Iowa State Univ. under contract No. W-7405-Eng-82.
1p.A. Hornung, A.D. Khan, D.R. Torgeson and R.G. Barnes, Z. Phys. Chemie Neue
Folge 116, 577-86 (1979).
i03 I PRE-PULSE SEQUENCE -- AN INVERSION PULSE (~) AND A
DELAY TIME (aT3): . =Fu-Tyan Lin, Department of Chemistry, University of
Pittsburgh, Pittsburgh, PA 15260 and Fu-Mel Lin, Calgon Corporation,
Pittsburgh, PA 152~-
The use of pre-pulse sequence which includes an inversion pulse
(~) and a delay time (D 2) to null the intensity of a selected peak in
NMR experiments was developed in this work. This delay time D 2
defined as aT 3 is applied right after W pulse and before the pulse
sequence for data acquisition. Here T 3 is a delay time to obtain
zero magnetization for a sufficient long dealy time D 1 before ~ pulse.
1
T 3 is equal to (2n2)T 1 derived from Bloch equations, and =(I - ~)T 1
measured from the experiments. For m~l~iple scans (n), the experi-
(n-l)T3 z
mental coefficient a = exp[- 4n(DI+A+I) ], where A is the free
induction decay (FID) acquisition time. For a single scan with
D 1 > 5T I, the a value becomes I. The presequence of inversion-delay
has the advantages of selective suppression, more easier and accurate
T 1 determination, and the separation of longer T 1 and shorter T 1 peaks
of a molecule.
150