Raman Scattering from Decoupled Phonon and Electron States in NpO₂

High Resolution Image Download MS PowerPoint Slide The Raman features of neptunium dioxide (NpO 2 ) and uranium–neptunium mixed oxides were investigated. Raman spectra of 16 O and 17 O-NpO 2 enriched sample were measured with excitation energy range of E i = 1.91–2.54 eV. Raman spectra of both NpO 2 samples and the uranium–neptunium rich mixed oxides show an asymmetry at low energies of the Γ 25′ (T 2g ) mode. The asymmetry was evidenced to originate from an electronic band at 431 cm –1 which originates from crystal field splitting. This assignment is in good agreement with theoretical models for NpO 2 with the hypothesis that the electron–phonon bound state is decoupled at high temperatures. The asymmetry of the Γ 25′ mode can be considered as a fingerprint of the NpO 2 lattice.