Molecular and ionic sublimation of neodymium, dysprosium, holmium, and erbium triiodides and thermochemistry of molecules and ions

Abstract

The molecular and ionic sublimation of neodymium, dysprosium, holmium, and erbium triiodides was studied by Knudsen effusion mass spectrometry. The monomer LnI3, dimer Ln2I6, and trimer Ln3I9 molecules and the ions LnI4– and Ln2I7– were found to be constituents of the saturated vapors in each case. The partial pressures of the vapor species and the equilibrium constants of the ion-molecular reactions were calculated. On the basis of a joint analysis of all literature data, the sublimation enthalpies ΔsHo(298.15 K)/(kJ mol−1) are recommended as 293 ± 3 (NdI3), 387 ± 30 (Nd2I6), 281 ± 3 (DyI3), 353 ± 12 (Dy2I6), 281 ± 3 (HoI3), 352 ± 6 (Ho2I6), 278 ± 4 (ErI3), and 350 ± 30 (Er2I6). The standard formation enthalpies ΔfHo(298.15 K)/(kJ mol−1) of the molecules and ions were determined to be −346 ± 5 (NdI3), −891 ± 30 (Nd2I6), −815 ± 23 (NdI4–), −1379 ± 46 (Nd2I7–), −336 ± 4 (DyI3), −880 ± 12 (Dy2I6), −811 ± 23 (DyI4–), −1360 ± 46 (Dy2I7–), −342 ± 4 (HoI3), −894 ± 7 (Ho2I6), −814 ± 23 (HoI4–), −1372 ± 46 (Ho2I7–), −341 ± 5 (ErI3), −888 ± 30 (Er2I6), −819 ± 23 (ErI4–), and −1377 ± 46 (Er2I7–).