On-line nuclear orientation

The combination of these three developments has led to the on-line nuclear orientation method (0LN0). A further advance of the technique has been the combination with NMR, which uses resonant rf perturbation of the nuclear polarization, yielding moment values to a few parts in 104. 

In this review the definition of orientation and orientation functions or orientation averages will be considered in detail. This will be followed by a comprehensive account of the information which can be obtained by three spectroscopic techniques, infra-red and Raman spectroscopy and broad line nuclear magnetic resonance. The use of polarized fluorescence will not be discussed here, but is the subject of a contemporary review article by the author and J. H. Nobbs 1. The present review will be completed by consideration of the information which has been obtained on the development of molecular orientation in polyethylene terephthalate and poly(tetramethylene terephthalate) where there are also clearly defined changes in the conformation of the molecule. In this paper, particular attention will be given to the characterization of biaxially oriented films. Previous reviews of this subject have been given by the author and his colleagues, but have been concerned with discussion of results for uniaxially oriented systems only2,3). 

The hfs and quadrupole tensors of one of the nitrogen ligands have been determined with ENDOR by Calvo et al.63). The 14N-ENDOR transition frequencies observed between 11 and 23 MHz were found to depend significantly on the nuclear quantum number mCu of the EPR observer line. These shifts are due to Cu-N crossterms (Sect. 3.2) and amount to more than 1 MHz for certain orientations of B0. ENDOR resonances of... 

This contribution concentrates on a discussion of some on-line techniques for ground state studies which are now under development and will be applied at ISOLDE in the near future. The plans for a nuclear-orientation set up at ISOLDE are outlined in the contribution to this symposium by N. Stone. 

Kashiwagi et al. ° have shown that Wright s data on Perspex are consistent with the predictions of a Ward aggregate model, using orientation functions obtained by broad line nuclear magnetic resonance. 

Since the splitting of the spectral lines is directly proportional to the magnetic field experienced by the nucleus, Mossbauer spectroscopy provides a very effective means by which this field may be measured. The transition probabilities between the nuclear substates affect the intensities of the lines in the Mossbauer spectrum which can therefore give information on the relative orientation of the magnetic field at the nucleus and the direction of propagation of the gamma-ray beam. 

Figure Al.4.4. The definition of the Euler angles (0, ( ), x) that relate the orientation of the molecule fixed (x, y, z) axes to the (X, Y, Z) axes. The origin of both axis systems is at the nuclear centre of mass O, and the node line ON is directed so that a right handed screw is driven along ON in its positive direction by twisting it from Z to z through 9 where 0 < 9 < n. ( ) and x have the ranges 0 to In. x is measured from the node line.

The lines in an EPR spectrum can be split by interaction of the electron spin with the nuclear magnetic moment of atoms on which the unpaired electron is located (Parish, 1990). Only atoms with nuclear spin (I) nonzero exhibit this type of interaction, which can be of two types (1) contact interaction that is isotropic and results from the delocalization of the unpaired electron onto the nucleus and (2) dipolar interaction between electron spin and the nucleus. In the second case, the interaction is dependent on orientation and, therefore, anisotropic (Campbell and Dwek, 1984). 

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