Localized 4f states and dynamic Jahn-Teller effect in PrO2

Neutron spectroscopic measurements of the magnetic excitations in PrO2 reve al (1) sharp peaks characteristic of transitions between levels of the 4f(1 ) configuration of Pr4+ split by the cubic crystal field, and (2) broad ban ds of scattering centered near 30 and 160 meV. We present a simple model ba sed on a vibronic Hamiltonian that accounts for these contrasting features of the data. The analysis shows that 90% +/- 10% of the Pr ions have a loca lized 4f(1) configuration and provides strong evidence for a dynamic Jahn-T eller effect in the Gamma (8) e lectronic ground state.