Exploring Optical and Vibrational Properties of the Uranium Carbonate Andersonite with Spectroscopy and First-Principles Calculations

Original periodic first-principles calculations based on the generalized gradient approximation combined with several analyses in microspectroscopy are presented for a hydrated uranium carbonate crystal, andersonite, possessing a specific channel structure. Infrared and ultraviolet visible absorption, Raman scattering, and steady-state and time resolved photoluminescence spectroscopy are used to address the atomic vibrations of water, uranyl, and carbonate ions, to determine the fluorescence decay time (around 220 mu s) and to estimate the amplitude of the optical gap (close to 3 eV). The role of structural water for andersonite stability is discussed by also performing calculations on a dehydrated model structure. Experiments and calculations address both the intrachannel and extra channel possibilities for the water molecules. The current research is a detailed study of a water-containing channel uranium system using a combined infrared/Raman treatment coupled with density functional theory calculation, providing new physical insight into the spectroscopic understanding of these channels.