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.