Vapor species over cerium and samarium trichlorides, enthalpies of formation of (LnCl3)n molecules and Cl−(LnCl3)n ions

A Knudsen effusion cell mass spectrometric technique was used to study vapor species over CeCl3 and SmCl3. Monomer, dimer, and trimer (Sm3Cl9) molecules, and LnCl4−, Ln2Cl7−, Ln3Cl10− (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 (ΔsH, 298 K, kJ·mol−1) to monomers and associated molecules obtained: 328 ± 6 (CeCl3), 306 ± 6 (SmCl3), 453 ± 16 (Ce2Cl6), 408 ± 12 (Sm2Cl6), and 468 ± 40 (Sm3Cl9). 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 (ΔfH, 298 K, kJ·mol−1) of molecules and ions have been calculated as follows: −730 ± 6 (CeCl3), −722 ± 6 (SmCl3), −1663 ± 16 (Ce2Cl6), −1649 ± 13 (Sm2Cl6), −2617 ± 40 (Sm3Cl9), −1250 ± 15 (CeCl4−), −1252 ± 15 (SmCl4−), −2184 ± 35 ­(Ce2Cl7−), −2172 ± 26 (Sm2Cl7−), −3183 ± 43 (Ce3Cl10−), and −3147 ± 43 (Sm3Cl10−). Copyright © 2001 John Wiley & Sons, Ltd.