51455 ESR Basic Unit

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For experiments on electron spin resonance in conjunction with the ESR control unit (514 57) or the ESR adapter (514 56).

The magnetic moment of the unpaired electron with the total angular momentum j in a magnetic field assumes the discrete energy states Em = � gj � BB � m � B where m = �j, �j + 1, ... , j BB = 9,274 � 10�24 J : Bohr�s magneton T gj: g factor When a high-frequency magnetic field with the frequency V is applied perpendicularly to the first magnetic field, it excites transitions between the adjacent energy states when these fulfill the resonance condition h � V = Em+1 � Em h: Planck�s constant. This fact is the basis for electron spin resonance, in which the resonance signal is detected using radio-frequency technology. The electrons can often be regarded as free electrons. The g-factor then deviates only slightly from that of the free electron (g = 2.0023), and the resonance frequency V in a magnetic field of 1 mT is about 78.0 MHz. The actual aim of electron spin resonance is to investigate the internal magnetic fields of the sample substance, which are generated by the magnetic moments of the adjacent electrons and nuclei. The first two experiments verify electron spin resonance in diphenyl-picryl-hydrazyl (DPPH). DPPH is a radical, in which a free electron is present in a nitrogen atom. In the simple configuration of the first experiment, the magnetic field B which fulfills the resonance condition is determined for three different resonance frequencies V. In the second experiment, the resonance frequencies can be set in a continuous range from 13 to 130 MHz. The aim of the evaluation in both cases is to determine the g factor. The object of the final experiment is to verify resonance absorption using a passive oscillator circuit.