Probehead with interchangeable loop‐gap resonators and rf coils for multifrequency EPR/ENDOR

A probehead employing interchangeable loop‐gap resonators and rf coils for multifrequency EPR/ENDOR spectroscopy from 1 to 10 GHz is described. A precision coupling mechanism allows accurate magnetic coupling of the microwaves to the resonators. The Rexolite© support of the resonator acts as a spool for the ENDOR coil. rf fields of 1.0 mT are generated. The coil and resonator can be easily changed to cover the range of 1–10 GHz. Liquid‐phase ENDOR spectra of the stable free‐radical galvanoxyl and of the spin label TEMPONE (4‐oxo‐2,2,6,6‐tetramethyl‐l‐piperidine‐N‐oxyl) dissolved in n‐heptane are shown. The ENDOR enhancement for nitrogen from TEMPONE is 15 times larger at 2.3 than at 9.3 GHz due to the rf enhancement.