A statistical theory for powder EPR in distributed systems

Abstract

A statistical interpretation is presented for "g strain," the dominant broadening in the EPR spectra of metallo-proteins. The direct cause of g strain is described by a three-dimensional tensor p, whose principal elements are random variables. The p and g tensors are not necessarily colinear. The observed EPR linewidth results from a distribution in the effective g value as a function of (a) the joint distribution function of the elements of the p tensor and (b) the spatial relationship between the two principal axis systems involved. The theory is reformulated in terms of matrices that facilitate a direct comparison with earlier work. Two previous theories of g strain represent different subsets of the general theory, namely, the case of zero rotation between axis systems and the case with nonzero rotation and full correlation between elements of the p tensor.