Transformation between cartesian and spherical tensors

A standard unitary transformation is proposed for interconversion between cartesian tensors and spherical tensors, and between expressions including such tensors. Methods for manipulating the transformation coefficients are described, and the effects of symmetry with respect to permutation of cartesian tensor suffices are discussed. As an example, the method is used to derive the angle-dependence of the circular intensity differential for Rayleigh scattering from a dimer.