AQUEOUS SAMPLE HOLDERS FOR HIGH-FREQUENCY ELECTRON-SPIN-RESONANCE

A quasioptical approach is utilized to design a resonator and sample h older for aqueous samples for high-frequency (250 GHz) electron spin r esonance (ESR) spectroscopy. A disk shaped sample geometry was chosen to match the field contours of the fundamental mode in a Fabry-Perot r esonator. A transmission-line analysis is used to determine the optimu m sample geometry while taking into account diffractive effects of the sample and the sample holder on the far infrared (FIR) radiation fiel d. FIR-ESR spectra of several aqueous solutions of nitroxide spin labe ls, including membrane vesicles and a labeled protein, are shown to de monstrate the success of the technique. (C) 1997 American Institute of Physics.