Thermodynamics of the evaporation of yttrium tribromide in the form of $\rm Y\rm Br_3$ and $\rm Y_2\rm Br_6$ molecules

Based on the results of a critical analysis of theoretical data on the structure and vibration frequencies of monomer and dimer molecules of yttrium tribromide, the molecular constants are chosen and the thermodynamic functions are calculated for $\rm Y\rm Br_3$ and $\rm Y_2\rm Br_6$. The data in the literature on the ratio of the partial pressures of dimer and monomer molecules are used to determine (according to the third law of thermodynamics) the enthalpy of the $\rm Y\rm Br_3$(cr, l) $\rm Y\rm Br_3$(g) $= \rm Y_2\rm Br_6$(g) reaction and to calculate the composition of yttrium bromide vapor in the temperature range of $1218$–$1492$ K, for which the data on the total pressure are known. It is established that the $P_{\mathrm{d}}/P_{\mathrm{m}}$ ratio increases from $0.06$ to $0.15$ in this temperature range. The values of the sublimation enthalpy of yttrium tribromide in the form of monomer and dimer molecules and the formation enthalpy of $\rm Y\rm Br_3$(g) and $\rm Y_2\rm Br_6$(g) are calculated based on the found partial pressures. The obtained values are added to the IVTANTERMO database.