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Chapter 3. Spin Systems
Figure 3.4: Experimental and calculated 133 Cs NMR spectra of a static powder sample of cesium cadmium thiocyanate.
Beta (p. 74)
LB (p. 28)
Polar angle, in degrees, of the internuclear vector in
the principal axis system of the electric field gradient tensor
Provides access to the convolution parameters for
the current site. To have individual convolution parameters for each site, specify this in the Spectrum
Default Parameters (p. 25) box
Background
In addition to the chemical shift anisotropy (CSA), the spectrum of a quadrupolar nucleus will also
depend on the nuclear quadrupolar interaction and the relative orientation of both interactions. The
quadrupolar interaction is considered up to second order for the observed nucleus. Optionally, dipolar and indirect coupling to a heteronucleus can be added (note: quadrupolar interaction, if any, is
neglected for the coupled heteronucleus).
3.4.1 Implementation Details
Specifically, we use the following conventions:
• the NQR notation is used for labelling the axes of the EFG tensor: |VZZ| >= |VYY| >= |VXX|
• the orientation of the field is given by the polar angle beta (wrt. VZZ) and the azimuth alpha,
the angle between the projection of B into the VXX-VYY plane and VXX (cf. Abragam)
• direction cosines of the shielding tensor with respect to the EFG frame are obtained via the Euler
angles following Arfken’s convention, with the initial alignment 11-XX, 22-YY, 33-ZZ
Figure 3.4 shows an example for the succesful simulation of a spectrum of a quadrupolar nucleus
that shows the combined effect of chemical shift anisotropy and quadrupolar interaction in a powder
sample. It is the 133Cs NMR spectrum of cesium cadmium thiocyanate, CsCd(SCN)3, and the results
51 [January 6, 2009]