Direct calculation of the orientational distribution function of partially ordered ensembles from the EPR line shape

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Abstract
We have developed a method for the determination of the orientational distribution function of partially ordered systems from the EPR line shape that is an alternative to the usual one of expansion in the elements of the Wigner rotation matrices. The method can be applied to distribution functions whose expansion in the rotation matrix elements are slowly convergent or where the EPR intensity cannot be computed analytically. It can also be used to extract geometrical information relating the principal magnetic axis system to the preferred direction of orientation. An application to a partially ordered ensemble of triplets observed in the photosynthetic bacterium Rps. viridis is given, and it is suggested that our technique may prove particularly valuable in analysis of biological systems.