Polarised atom sources

This phenomenon, first pointed out by Fano [143] and called the Fano effect, has been used to produce spin-polarised electron sources [144]. Sources based on irradiating atoms are now mainly of academic importance, because solid state sources based on GaAs devices yield a higher current more simply. 

By comparison, 3D HCCH COSY experiments are a little simpler (Figure 5.22). An initial pulse develops transverse magnetisation in aliphatic H nuclei (specifically C - H atoms) (source nuclei I) (Fi) that evolves according to chemical shift before polarisation transfer... 

There are also nucleophilic displacement reactions, of considerable synthetic importance, in which the attacking atom in the nucleophile is carbon in either a carbanion (p. 288) or a source of negatively polarised carbon (cf. p. 221) new carbon-carbon bonds are thus formed ... 

The need for improved background correction performance has generated considerable interest in applying the Zeeman effect, where the atomic spectral line is split into several polarised components by the application of a magnetic field. With a Zeeman effect instrument background correction is performed at, or very close to, the analyte wavelength without the need for auxiliary light sources. An additional benefit is that double-beam operation is achieved with a very simple optical system. 

State selection and focussing of atoms by magnetic fields has been extensively reviewed over several decades (e.g. Ramsay, 1956 Reuss, 1988 lanotta, 1988), and only a brief description of a source of spin-polarised hydrogen atoms will be given here. 

This Coulombic interaction is called a hydrogen bond, and is a source of stabilisation in a variety of molecules, in particular in those that have an atom bearing a negative charge that is close to a polarised hydrogen atom. For example, such a configuration is present in ortho-hydroxybenzoic acid after the carboxylic acid group has been deprotonated. Draw the resultant anion. 

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