Continuous Wave Electron-Nuclear DOuble Resonance Spectroscopy
CW ENDOR involves the continuous exposure of the sample to both microwaves and rf.
In CW ENDOR, the magnetic field is set to be in resonance with a specific EPR transition. The microwave power is adjusted to a power in which the signal is being saturated. This is due to an equalization of the α and β populations. The frequency of the rf is then swept and the return of the EPR transition intensity is monitored. When the rf is in resonance with a nuclear transition, spins are transferred from one of the electronic states, thus yielding inequivalent populations again. As with CW EPR, the signal is modulated. However, instead of modulating the magnetic field, the frequency or amplitude of the rf is modulated, giving rise to derivative line shapes similar to those observed in typical CW EPR.