  The angular distribution and linear polarization of the fluorescence light
following the resonant photoexcitation is investigated within the framework of
the density matrix and second-order perturbation theory. Emphasis has been
placed on "signatures" for determining the level sequence and splitting of
intermediate (partially) overlapping resonances, if analyzed as a function of
the photon energy of the incident light. Detailed computations within the
multiconfiguration Dirac-Fock method have been performed especially for the
$1s^{2}2s^{2}2p^{6}3s\;\, J_{i}=1/2 \,+\, \gamma_{1} \:\rightarrow\:
(1s^{2}2s2p^{6}3s)_{1}3p_{3/2}\;\, J=1/2, \, 3/2
  \:\rightarrow\: 1s^{2}2s^{2}2p^{6}3s\;\, J_{f}=1/2 \,+\, \gamma_{2}$
photoexcitation and subsequent fluorescence emission of atomic sodium. A
remarkably strong dependence of the angular distribution and linear
polarization of the $\gamma_{2}$ fluorescence emission is found upon the level
sequence and splitting of the intermediate $(1s^{2}2s2p^{6}3s)_{1}3p_{3/2}\;\,
J=1/2, \, 3/2$ overlapping resonances owing to their finite lifetime
(linewidth). We therefore suggest that accurate measurements of the angular
distribution and linear polarization might help identify the sequence and small
splittings of closely-spaced energy levels, even if they can not be
spectroscopically resolved.
