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

Abstract

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 LaBr 3 and La 2 Br 6 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 LaBr 3 in the form of monomers and dimers. In ionic sublimation studies, the emission of the Br -, , and negative ions was recorded in both regimes. Studies of the ionic sublimation of LnX 3 single crystals were shown to give reliable data on the thermochemical properties of negative ions.

Molecular and ionic sublimation of neodymium tribromide polycrystals and single crystals

“…This study of neodymium tribromide sublimation continues our systematic investigation of the molecular and ionic sublimation of lanthanide tribromide polycrystals under equilibrium conditions (Knudsen effusion) and lanthanide tribromide single crystals under conditions of free evaporation from an open surface (Langmuir evaporation) [1][2][3][4][5].…”

Composition of saturated vapor over Ytterbium bromides

“…4 The Knudsen method is a semidynamic technique in which even a small sampling of particular molecules can in certain cases play an important role during reactions in the condensed phase [28]. 5 In accordance with the well known regularities for molecules of lanthanide halogenides Ln 2 X 2n (n = 1-3) [17][18][19][20][21], the channel of dissociative ionization with the cleavage of one bromine atom and formation of ions is most likely upon the inter action of such associates with electrons. obtained in this work are in close agreement with the data [2] obtained at low temperatures of the studied range.…”

“…1, the mass spectra of vapor differ considerably at different stages, this distinction comprising not only the qualitative change in the ratios of ion currents but the complete vanishing of and Br + ions from the mass spectrum at stage II as well. We note that at both stages, the mass spectra differ from those of lanthanide tribromides [17][18][19][20][21]. The phenomena that stand out in particular are a very high fraction of YbBr + ion and a wide variety of ions con taining two ytterbium atoms.…”

“…The energy scale in Fig. 2 was calibrated with respect to the ion, since it forms only as a result of the ionization of YbBr 3 molecules (by analogy with other lanthanide tribromides [17][18][19][20][21]) and corre sponds to a so called "pure line" in the mass spectrum. The ion appearance energy AE( , YbBr 3 ) = 9.5 ± 0.5 eV, which is the same as the ionization energy I 0 of 2 According to the assumption in [22] on possibility of ignoring the dissociative ionization of Br 2 , the ratio between ion currents of Br + and corresponds to the equilibrium constant of reac tion Br 2 = 2Br.…”

Thermodynamic parameters of vaporization of EuBr2

“…Note that in work [5], where the lowest pressure p(EuBr 2 ) was obtained, no dimer molecules were registered in the vapor. Our more detailed analysis of the results is based on the detection of the temperature course of sublima tion enthalpies calculated according to the third law, and on our comparison of sublimation entropies experimentally determined using the second law with those theoretically calculated [20]. The results of this analysis are shown in Fig.…”