High-Pressure Studies of Cesium Uranyl Chloride

The pressure behavior of crystalline Cs₂UO₂Cl₄ has been explored using a diamond anvil cell. The uranyl fluorescence intensity decreases dramatically with increasing pressure. Using the O-U-O symmetric stretching frequency, an apparent linear decrease in bond length with increasing pressure was observed. A linear decrease in fluorescence intensity with increasing pressure was attributed to a large growth in the nonradiative relaxation, likely attributed to increased relaxation through phonon modes. Quantum theory of atoms in molecules calculations and ab initio wave function methods (CASSCF) support the U≡O bond in UO₂²⁺ being highly sensitive to the bond distance, but negligibly affected by the U-Cl bond length.