Vapor species over cerium and samarium trichlorides, enthalpies of formation of (LnCl 3 ) n molecules and Cl − (LnCl 3 ) n ions

A Knudsen effusion cell mass spectrometric technique was used to study vapor species over CeCl 3 and SmCl 3 . Monomer, dimer, and trimer (Sm 3 Cl 9 ) molecules, and LnCl 4 − , Ln 2 Cl 7 − , Ln 3 Cl 10 − (Ln = Ce, Sm) negative ions, were observed in saturated vapor in the temperature range 958–1227 K. Partial vapor pressures of neutral constituents were determined and the enthalpies of sublimation (Δ s H , 298 K, kJ·mol −1 ) to monomers and associated molecules obtained: 328 ± 6 (CeCl 3 ), 306 ± 6 (SmCl 3 ), 453 ± 16 (Ce 2 Cl 6 ), 408 ± 12 (Sm 2 Cl 6 ), and 468 ± 40 (Sm 3 Cl 9 ). Equilibrium constants for various chemical reactions were measured and the enthalpies of reactions obtained using the second and third laws of thermodynamics. The enthalpies of formation (Δ f H , 298 K, kJ·mol −1 ) of molecules and ions have been calculated as follows: −730 ± 6 (CeCl 3 ), −722 ± 6 (SmCl 3 ), −1663 ± 16 (Ce 2 Cl 6 ), −1649 ± 13 (Sm 2 Cl 6 ), −2617 ± 40 (Sm 3 Cl 9 ), −1250 ± 15 (CeCl 4 − ), −1252 ± 15 (SmCl 4 − ), −2184 ± 35 (Ce 2 Cl 7 − ), −2172 ± 26 (Sm 2 Cl 7 − ), −3183 ± 43 (Ce 3 Cl 10 − ), and −3147 ± 43 (Sm 3 Cl 10 − ). Copyright © 2001 John Wiley & Sons, Ltd.