Electron Nuclear Double Resonance (ENDOR) is a spectroscopic technique used to investigate the interactions between unpaired electrons and nuclear spins in a molecule or material. It is a combination of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopy.
ENDOR is primarily employed to study the electron-nuclear spin interactions in systems containing paramagnetic species, such as free radicals or transition metal ions. It utilizes the principle of resonance, where the electron spin is excited by microwave radiation, leading to changes in the nuclear spin state. This resonance induces transitions between the energy levels of both the electron and nuclear spins, allowing for the detection and analysis of these interactions.
In ENDOR experiments, a narrow-bandwidth microwave source is used to excite the electron spin system, while the nuclear spin system is probed using radiofrequency (RF) pulses from an NMR spectrometer. By varying the frequency and power of these radiation sources, the resonant frequencies of both electron and nuclear spins can be determined, providing detailed insight into the coupling between them.
ENDOR spectroscopy finds wide application in various scientific fields, including physics, chemistry, and biology. It provides valuable information about the geometric and electronic structure of paramagnetic centers, their interactions with nearby nuclei, and their dynamics in diverse systems. ENDOR techniques have contributed to the understanding of fundamental phenomena, such as electron transfer reactions, spin-spin interactions, and the behavior of radicals in organic and inorganic compounds.
