An improved line shape model for the matrix ENDOR response in disordered systems

An improved line shape model for the matrix ENDOR response near the free-nucleus precession frequency in disordered systems is developed and applied to a spin system with S=1/2 and I=1/2 using a density matrix formalism. The model includes the radiofrequency and microwave field intensities as well as different spin relaxation paths explicitly. Application of this model to trapped electrons in 2-methyltetrahydrofuran glass gives geometrical and magnetic data which are in excellent agreement with existing data from electron spin echo experiments. The effects of the various parameters in the theory of the matrix ENDOR line shape are discussed.