Frequency dependence of EPR signal intensity, 250 MHz to 9.1 GHz

Experimental EPR signal intensities at 250 MHz, 1.5 GHz, and 9.1 GHz agree within experimental error with predictions from first principles. When both the resonator size and the sample size are scaled with the inverse of RF/microwave frequency, omega, the EPR signal at constant B-1 scales as omega(-1/4). Comparisons were made for three different samples in two pairs of loop gap resonators. Each pair was geometrically scaled by a factor of 6. One pair of resonators was scaled from 250 MHz to 1.5 GHz, and the other pair was scaled from 1.5 GHz to 9 GHz. All terms in the comparison were measured directly, and their uncertainties estimated. The theory predicts that the signal at the lower frequency will be larger than the signal at the higher frequency by the ratio 1.57. For 250 MHz to 1.5 GHz, the experimental ratio was 1.52 and for the 1.5-GHz to 9-GHz comparison the ratio was 1.14. (C) 2002 Elsevier Science (USA).