  The Raman spectrum of plutonium dioxide is studied both experimentally and
theoretically. Particular attention has been devoted to the identification of
high-energy modes at $2120$ cm$^{-1}$ and $2625$ cm$^{-1}$, the attribution of
which has so far been controversial. The temperature dependence of both modes
suggests an electronic origin. Crystal Field (CF) calculations reported in this
work shows that these two modes can be respectively assigned to the
${\Gamma}_{1}$ $\rightarrow$ ${\Gamma}_{5}$ and ${\Gamma}_{1}$ $\rightarrow $
${\Gamma}_{3}$ CF transitions within the $^{5}I_{4}$ manifold. These two modes,
together with the only vibrational line foreseen by the group theory for the
Fm${-3}$m PuO$_{2}$ symmetry the T$_{2g}$ PuO stretching mode observed at $478$
cm$^{-1}$ can thus be used as Raman fingerprint of fcc plutonium dioxide.
