The thermodynamic characteristics of vaporization of praseodymium triiodide

The vaporization of praseodymium triiodide was studied by high-temperature mass spectrometry. Monomeric (PrI₃) and dimeric (Pr₂I₆) molecules and the PrI ₄ ^? and Pr₂I ₇ ^? negative ions were recorded in saturated vapor over the temperature range 842–1048 K. The partial pressures of neutral vapor components were determined. The enthalpies of sublimation Δ_s H ^o(298.15 K) in the form of monomers (291 ± 10 kJ/mol) and dimers (400 ± 30 kJ/mol) were calculated by the second and third laws of thermodynamics. The equilibrium constants of ion-molecular reactions were measured and the enthalpies of the reactions determined. The enthalpies of formation Δ_f H ^o(298.15 K) of molecules and ions in the gas phase were calculated (?373 ± 11, ?929 ± 31, ?865 ± 25, and ?1433 ± 48 kJ/mol for PrI₃, Pr₂I₆, PrI ₄ ^? , and Pr₂I ₇ ^? , respectively).