Sublimation enthalpies of terbium and lutetium triiodides and formation enthalpies of their monomer and dimer molecules

Abstract

The sublimation of terbium and lutetium triiodides was studied by Knudsen effusion mass spectrometry. The temperature dependencies of partial vapor pressures [atm] of the monomer and dimer molecules were determined as: lnp(TbI3) = – (31.74 ± 0.24)× 103/T + (21.43 ± 0.29) for 743–906 K; lnp(Tb2I6) = – (38.66 ± 0.38)× 103/T + (25.63 ± 0.46) for 786–906 K; lnp(LuI3) = – (31.48 ± 0.25)× 103/T + (22.28 ± 0.30) for 721–951 K; and lnp(Lu2I6) = – (36.95 ± 0.37)× 103/T + (25.21 ± 0.43) for 796–950 K. On the basis of a joint analysis of all literature data, the sublimation enthalpies [kJ mol–1] at 298.15 K are recommended as 281 ± 3 (TbI3), 346 ± 30 (Tb2I6), 279 ± 12 (LuI3), and 340 ± 30 (Lu2I6). The standard formation enthalpies [kJ mol–1] of the gaseous species at 298.15 K are –343 ± 4 (TbI3), –902 ± 30 (Tb2I6),–326 ± 12 (LuI3), and –870 ± 30 (Lu2I6).