V. B. Motalov

A Mass Spectrometric Study of the Molecular and Ionic Sublimation of Lanthanum Tribromide

The molecular and ionic composition of vapor over lanthanum tribromide was studied by high-temperature mass spectrometry under the conditions of sublimation from a Knudsen effusion cell and from an open single crystal surface. The partial pressures of LaBr3 and La2Br6 in saturated vapor and the ratio between their sublimation coefficients under free vaporization conditions were determined. The second and third laws of thermodynamics were used to calculate the enthalpies of sublimation of LaBr3 in the form of monomers and dimers.In ionic sublimation studies, the emission of the Br−, LaBr4−, and La2Br7t- negative ions was recorded in both regimes. Studies of the ionic sublimation of LnX3 single crystals were shown to give reliable data on the thermochemical properties of negative ions.

A Mass Spectrometric Study of the Sublimation of Lutetium Tribromide under Knudsen and Langmuir Conditions

AbstractThe molecular and ionic sublimation of lutetium tribromide under thermodynamic equilibrium (Knudsen effusion) conditions and from the open surface of a LuBr3 single crystal (Langmuir conditions) was studied by high-temperature mass spectrometry. Vapor contained the LuBr3, Lu2Br6, Lu3Br9, and Lu4Br12 molecules and the Br−, LuBr4−, Lu2Br7−, and Lu3Br10− negative ions. The partial pressures of the molecules in saturated vapor and the ratio between the sublimation coefficients of monomers and dimers under free vaporization conditions were determined. The degree of the electron impact-induced fragmentation of LuBr3 molecules under Knudsen and Langmuir sublimation conditions was analyzed. The second and third laws of thermodynamics were used to calculate the enthalpies of sublimation in the form of monomers and oligomers (Knudsen vaporization) and the corresponding activation energies of sublimation (Langmuir vaporization). Ion—molecular equilibria with the participation of negative ions were studied. The enthalpies of formation of molecules and ions in the gas phase were obtained.

The Thermodynamic Parameters of Monomer and Dimer Molecules of Cerium and Praseodymium Tribromides

AbstractThe method of high-temperature mass spectrometry is used for studying the composition of saturated vapor over cerium and praseodymium tribromides. Monomer and dimer molecules are found in the temperature ranges of 789–994 K and 804–957 K for cerium and praseodymium, respectively. The partial pressures of vapor components are determined, p(Pa), the temperature dependences of which are approximated by the equations

A jump change in the sublimation coefficient of the PrBr3 single crystal at the polymophic transition point

\begin{gathered} \log p(CeBr_3 ) = ( - 14.63 \pm 0.08) \times 10^3 /T + (14.54 \pm 0.09), T = 789 - 994 K; \hfill \\ \log p(Ce_2 Br_6 ) = ( - 19.72 \pm 0.61) \times 10^3 /T + (17.60 \pm 0.64), T = 918 - 980 K; \hfill \\ \log p(PrBr_3 ) = ( - 14.13 \pm 0.12) \times 10^3 /T + (14.09 \pm 0.14), T = 804 - 957 K; \hfill \\ \log p(Pr_2 Br_6 ) = ( - 18.90 \pm 0.50) \times 10^3 /T + (17.15 \pm 0.53), T = 903 - 955 K. \hfill \\ \end{gathered}

Thulium Trichloride: Thermochemistry of Molecular and Ionic Associates

The values of pressure of vapor components are used along with literature data for the calculation of enthalpies of sublimation in the form of monomer and dimer molecules by the procedures of the second and third laws of thermodynamics. Based on analysis of the results, thermodynamic parameters of monomer and dimer molecules (in kJ mol−1) are recommended,

The thermodynamic activities of the components of NaI-PrI3 system melts

\begin{gathered} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta _s H^0 (CeBr_3 , 298.15) = 305 \pm 5, \Delta _s H^0 (PrBr_3 , 298.15) = 293 \pm 5, \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta _s H^0 (Ce_2 Br_6 , 298.15) = 410 \pm 28, \Delta _s H^0 (Pr_2 Br_6 , 298.15) = 403 \pm 28, \hfill \\ \,\,\,\,\,\,\,\Delta _f H^0 (CeBr_3 , gas, 298.15) = - 587 \pm 6, \Delta _f H^0 (PrBr_3 , gas, 298.15) = - 597 \pm 7, \hfill \\ \Delta _f H^0 (Ce_2 Br_6 , gas, 298.15) = - 1372 \pm 28, \Delta _f H^0 (Pr_2 Br_6 , gas, 298.15) = - 1378 \pm 28. \hfill \\ \end{gathered}