Phase Behaviors of Saturation Transfer ESR Signals at High Microwave Fields

Abstract

The phase behavior of saturation transfer electron spin resonance (ST-ESR) was studied with the use of the second harmonic absorption (V₂) spectrum of the spin label (2,2,6,6-tetramethylpiperidine-1-oxyl) in glycerol-water solution. Upon application of an intense microwave field (0.508 G), a pronounced nonzero component was observed at the modulation phase where the peak-to-peak amplitude is expected to be zero. This component is the saturation transfer spectrum which is latent at the phases giving intense V₂ signals. A single intergration of these obtained spectra yields a significant integrated value which varies in a sinusoidal manner. The phase discrepancy was found to be 70 degrees between the variations of the peak-to-peak amplitude and the integrated value.