Paramagnetic perturbations

Cobalt can act as an electron spin resonance, absorption spectral and nuclear resonance probe. It can also be used as a proton probe because its paramagnetism perturbs the proton resonances of neighbouring organic groups. The probe properties of cobalt are described by Foster et al. 

A knowledge of the basic theory of the paramagnetic interaction is useful to pursue a better exploitation of the effects induced by the paramagnetic perturbation. 

Electron spin resonance (or electron paramagnetic resonance) is now a well-established analytical technique, which also offers a unique probe into the details of molecular structure. The energy levels involved are very close together and reflect essentially the properties of a single electronic state split by a small perturbation. 

The very weak Tm - So transitions are hard to observe directly by absorption spectroscopy. Even with long cells, the high concentrations required present solubility — and what is more important — purity problems. An impurity of 1 10 may give rise to absorption bands which have the same intensity as the expected Ti So absorption. The experimental conditions, therefore, have to be chosen to allow an increase of the Ti- - So oscillator strength to be achieved through perturbation by paramagnetic species (O2 or NO) or heavy atoms. Alternatively, an indirect method, phosphorescence excitation spectroscopy, which has high sensitivity and selectivity, may be applied. 

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