Is the reliable evaluation of thermal functions for f-elements and their compounds in the gaseous state possible today

To evaluate accurate values of thermal functions for gases, both an adequate method of calculation and sufficiently complete information on electronic-vibrational-rotational energy levels of molecules (atoms) are required. At moderate temperatures the principal difficulties for f-elements and their compounds are due to scarcity or even absence of the data on energy levels and molecular constants. The problems which are caused by poor knowledge of molecular structure and electronic states are considered for mono-, di- and polyatomic gases. The inaccuracies of calculated thermal functions are discussed. (orig.)