th  - 1988 - 51st ENC Conference

19 I DIPOLARAND SPIN-ROTATION POLARIZATION OF METHYL GROUP SPINS
Michael Murphy and David White, Dept. of Chemistry
University of Pennsylvania, Philadelphia, PA 19104
We have investigated the proton NMR of molecules such as CH3CN , CH3CmCH ,
and CH3CI trapped at low concentrations in solid Kr. The methyl groups in
these matrices undergo nearly free quantum rotation, allowing for polarization
of methyl spins to occur via coupled spin and rotational relaxation following
a temperature jump. Besides proton-proton dipolar polarization (the 'Haupt
I
effect' ), we have identified additional spin polarizations, namely, those
associated with secular spin-rotation and heteronuclear dipolar interactions.
Due to the magnetic isolation of the molecules, well-resolved powder line-
shapes are obtained from which the contributions of different spin observables
may be distinguished. We provide evidence that a finite spin-rotation cou-
pling exists and determine the coupling constant for CH3CN/Kr by examining the
signal component due to polarized 'spin-rotation magnetization'. Heteronuclear
2 Is
dipolar polarization is demonstrated in CH3CN/Kr. Lineshape analyses are
shown to provide new information regarding the methyl group rotational levels.
I. J. Haupt, Phys. Lett. 38A, 389 (1972); Z. Naturforsch 28a, 98 (1973)
2. M. Murphy and D. White, J. Chem. Phys. 86, 1640 (1987)
I -- 2 0 I NMR SIGNAL PROCESSING USING PADE APPROXIMANT AND LINEAR
PREDICTION Z-TRANSFORM METHOD: J. Tang*, Y. Zeng and J. R. Norris, Chemistry Division,
Argonne National Laboratory, Argonne, IL 60439
Linear prediction (LP) theory has been widely applied to digital signal processing to overcome
truncation and noise problems often encountered by the fast Fourier transform method. Here, a new
approach 1 is proposed for NMR spectral analysis with enhanced resolution and sensitivity using Pad6
rational approximation 2-s and linear prediction z-transform. 4 In the conventional LP methods 4 such as
LPQRD or LPSVD, the whole spectrum is analyzed. In order to resolve all the spectral lines a very large
LP filter length, usually several times that of the total number of spectral components, has to be used.
In contrast, this method can be used to zoom into a small section of the whole spectrum for analysis if
the spectral contents in some zones are of particular interest. Thus, this method uses a much shorter
LP filter length and requires a smaller computer memory and shorter computational time. As LPQRD or
LPSVD, this method also yields a table of spectral parameters without additional efforts required by FFT.
Applications of this method and the comparisons with LPQRD or LPSVD will be presented. Other LP
methods using computationally efficient autoregression (AR) or Burg algorithm s are particularly useful for
2-D NMR signal processing. By LP extrapolation of the unobserved FID and application of line-
narrowing apodization functions one can significantly improve spectral resolution while avoiding sinc-
wiggling artifacts due to data truncation.
.
2.
3.
4.
.
J. Tang and J. R. Norris, Nature, (in press).
E. Yeramian and P. Claverie, Nature 326, 169 (1987).
J. Tang and J. R. Norris, J. Magn. Reson. (in press).
J. Tang and J. R. Norris, in "Electronic Magnetic Resonance of the Solid State', Vol. 1, p. I11
(1987) (Ed., J. Weil), The Canadian Society for Chemistry, Ottawa, Canada.
J. Tang and J. R. Norris, Chem. Phys. Lett. 131, 252 (1986).
This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences,
Division of Chemical Sciences under contract W-31-109-Eng-38.
107