Experimental Considerations: Instrumentation and Methodology
The great majority of electron paramagnetic resonance (EPR) experiments performed during the past 20 years have been conducted utilizing commercial X-band EPR spectrometers of one of the two versions. During much of this time, the design of commercial EPR spectrometers has changed little; however, this situation is likely to change dramatically in the next few years. The magnetic field needed to observe EPR is produced by a low impedance electromagnet and current-stabilized magnet power supply. A Hall effect field controller, which is common to all commercial EPR spectrometers, provides a field proportional regulation of the magnetic current supply. The field regulator produces a voltage that is proportional to the magnetic field strength, making use of the Hall voltage from a thermostated Hall probe; the absolute accuracy of the field calibration depends on the linearity of the Hall device. Several workers have devised experimental techniques to circumvent the problem of defining phase angle.