Mass spectrometric investigation of neutral and charged constituents in saturated vapor over PrI3

The Knudsen effusion mass spectrometric technique was used to study vapor species over praseodymium triiodide. The monomer, PrI3, and dimer, Pr2I6, molecules and the negative ions, PrI4− and Pr2I7−, were observed in saturated vapor in the temperature range from 856 K to 1048 K. The partial vapor pressures of neutral constituents were determined and the enthalpies of sublimation obtained using the second and the third laws of thermodynamics (ΔsH°(298.15 K) = 291 ± 4 kJ mol−1 for PrI3, and ΔsH°(298.15 K) = 400 ± 30 kJ mol−1 for Pr2I6). The equilibrium constants for various ion molecular reactions were measured and the enthalpies of reactions obtained. The enthalpies of formation, ΔfH°(298.15 K) kJ mol−1, of gaseous molecules and ions were calculated and are as follows: −374 ± 6 (PrI3), −929 ± 30 (Pr2I6), −867 ± 30 (PrI4−), −1432 ± 50 (Pr2I7−).