Molecular and ionic sublimation poly- and single crystals of gadolinium tribromide
The molecular and ionic sublimation of poly- and single crystals of gadolinium tribromide was studied in the Knudsen and Langmuir regimes. In the temperature range of 894 - 1044 K the monomer and dimer molecules and GdBr<sub>4</sub><sup>-</sup> and Gd<sub>2</sub>Br<sub>7</sub><sup>-</sup> negative ions were observed. The partial vapor pressure of neutral species were determined and the sublimation enthalpies (Δ<sub>s</sub>H°(298 K), kJ mol<sup>-1</sup>) in the form of monomer (296 ± 5) and dimer (384 ± 28) were obtained. The equilibrium constants of ion molecular reactions including GdBr<sub>4</sub><sup>- </sup>and Gd<sub>2</sub>Br<sub>7</sub><sup>- </sup>ions were measured and the reaction enthalpies were calculated. The enthalpies of formation (Δ<sub>f</sub>H°(298 K) kJ mol<sup>-1</sup>) of molecules - 542 ± 6 (GdBr<sub>3</sub>), -1292 ± 28 (Gd<sub>2</sub>Br<sub>6</sub>) and ions - 1070 ± 27 (GdBr<sub>4</sub><sup>-</sup>) and - 1844 ± 50 (Gd<sub>2</sub>Br<sub>7</sub><sup>-</sup>) are recommended.