On the Raman Spectrum of Plutonium dioxide: vibrational and crystal electric field modes

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 Γ1 Γ5 and Γ1 Γ3 CF transitions within the 5 I4 manifold. These two modes, together with the only vibrational line foreseen by the group theory for the Fm-3m PuO2 symmetry – the T2g Pu-O stretching mode observed at 478 cm-1 – can thus be used as Raman fingerprint of fcc plutonium dioxide.