Structure and Thermodynamics of Uranium(VI) Complexes in the Gas Phase: A Comparison of Experimental and ab Initio Data

Ab initio methods were applied for the calculation of the total energy and the molar entropy and heat capacity of the compounds UO<INF>2</INF>F<INF>2</INF>, UO<INF>2</INF>(OH)<INF>2</INF>, UF<INF>6</INF>, and UO<INF>3</INF> in the gas phase with the purpose to obtain thermodynamic data for reactions that can be compared with experimental values. The total energy, geometry, and vibration frequencies were calculated at different levels of accuracy:  second-order perturbation theory (MP2), coupled cluster theory (CCSD(T)), and density functional theory (B3LYP). Our results agree well with experimental values and previous theoretical results. Additionally, the transition state of UO<INF>2</INF>F<INF>2</INF>(g) was studied and the value of the barrier for the inversion of the fluoride atoms was calculated.