A new approach to the theory of linear dichroism in partially ordered systems. Application to reaction centers and whole cells of photosynthetic bacteria.

We have developed a new approach to the theory of linear dichroism in partially ordered systems. The description of the partially ordered ensemble uses a density of states function, D(theta, phi, approximately delta), which gives the probability that the direction of polarization for incident polarized light has spherical angles theta and phi in an axis system fixed with respect to the molecule; approximately delta = (delta 1, delta 2...delta n) is a set of parameters that describes the partial ordering. We derive new formulas for linear dichroism using the density of states function and then apply these formulas to the analysis of linear dichroism in reaction centers and whole cells of photosynthetic bacteria. One advantage of our approach is that the order parameter, approximately delta, provides a more complete description of the distribution function than the traditional order parameters used by other authors. Knowledge of approximately delta gives a good physical description of the partial ordering and allows one to calculate accurate limits for the range of possible orientations of the transition moments.