Nonempirical Studies of the Molecular Properties and Thermodynamic Functions of Urea in the Ideal Gas State

摘要

Quantum-chemical calculations were performed for the equilibrium structure of isolated urea mol-ecules using the 6-311++G** basis set and second-order Moller–Plesset perturbation theory, density functionaltheory, and the coupled cluster method with the local inclusion of electron correlation. The results were used toperform statistical calculations of the standard thermodynamic functions of urea in the ideal gas state taking intoaccount anharmonicity of normal vibrations. The contributions of dimerization and isomerization of urea mol-ecules in the vapor phase were determined. The recommended values were compared with the availableexperimental data and the results of preceding calculations.