Thermodynamics of the Evaporation of Yttrium Triiodide in the Form of YI3 and Y2I6 Molecules

In this paper, we select the values of the molecular constants and calculate the thermodynamic functions for YI 3 and Y 2 I 6 based on a critical analysis of experimental and theoretical data on the structure and vibration frequencies of the monomeric and dimeric forms of yttrium triiodide molecules. Using the literature data on the ratio of the partial pressures of dimeric and monomeric molecules and the third law of thermodynamics, we determine the enthalpy of YI 3 (cr., l) + YI 3 (g) = Y 2 I 6 (g) reaction and calculate the composition of the yttrium iodide vapor in the temperature range of 800–961 K, for which there are literature data on the total pressure. In the considered temperature range, P d / P m pressure ratio is found to increase from 0.003 to 0.014. The partial pressures determined are used to calculate the sublimation enthalpies of yttrium triiodide in the form of monomeric and dimeric molecules and the enthalpies of formation of these molecules. The obtained values have been entered into the database of the IVTANTERMO software package.