PNNL

Abstract

Multiple resonance methods are important tools in EPR for revealing the network of hyperfine levels of free radicals and paramagnetic centers. The variations of electron nuclear double resonance (ENDOR) or electron spin echo envelope modulation (ESEEM) techniques help to correlate nuclear frequencies with each other. These methods have limited utility when there is overlap or suspected overlap between different species or different orientations in the EPR spectrum. Overlap and second order shifts of lines in the ENDOR spectrum also leads to ambiguity in interpretation. A new electron nuclear mutiple resonance method is presented here, that is based on population transfer ENDOR. It is a quadruple resonance method that correlates ENDOR lines and reveals the network of hyperfine levels in unoriented samples and in samples with overlapping EPR or ENDOR lines.