Analysis of saturation transfer electron paramagnetic resonance spectra in terms of amplitude and phase.

A systematic analysis of saturation transfer (ST) electron paramagnetic resonance spectroscopy was developed to separate an observed absorption signal either into an amplitude and a phase spectrum or into an in-phase and an ST spectrum. We established a phase reference procedure, replacing the low-power phase null method by a high-power phase maximum method. This is an extension of the finding that a peak-to-peak height and a single integration of the second harmonic absorption display vary sinusoidally as functions of the modulation phase [Y. Shimoyama and H. Watari, Appl. Spectrosc. 39, 170 (1985)]. Based on the sinusoidal variation in the peak-to-peak height, we found a phase shift at each magnetic field and could evaluate the amplitude and phase of a signal vector. The sinusoidal variation of the single integrated value allowed the absorption signal to be separated into an in-phase and an ST spectrum. The high-power phase maximum method provides a remedy of the phase setting problem in ST spectroscopy by which the in-phase signal can be detected at any microwave field. [ABSTRACT FROM AUTHOR]