On the measurement of molecular anisotropies using laser techniques. I. Polarized laser fluorescence

The tensor density matrix formalism is used to derive expressions for the circular and linear polarization of laser-induced fluorescence from molecules which have an anisotropic distribution in the spatial orientation of their ground state angular momentum components. The generalized anisotropic distribution is expressed as a series of state multipolar moments and it is shown that the excited state multipolar moments created therefrom by the absorption of laser radiation may be quite complex even in the absence of perturbations which cause cross relaxation. Under these circumstances, polarized laser fluorescence does not give an unambiguous measure of the ground state multipolar moments and in succeeding papers we discuss methods which do yield these quantities without ambiguity.