Molecular and ionic sublimation of neodymium tribromide polycrystals and single crystals

Abstract

The molecular and ionic sublimation of polycrystals and single crystals under Knudsen effusion and Langmuir evaporation conditions is reported. In both sublimation regimes, the sublimation product at 780-1050 K contains neodymium tribromide monomer and dimer molecules, as well as the negative ions , and Br -

Mass-spectrometric study of molecular and ionic sublimation of gadolinium and terbium tribromides in Knudsen and Langmuir modes

“…3, where temperature dependences of relative partial ionization cross sections Ф (ratio of the current of ions of a specified type to a total current of all ions formed from a given molecule) for single-charged ions are presented. We have noted an analogous effect also for others tribromides [1][2][3][4][5][6]. In our opinion its nature is connected with essential polarization of adsorbed molecules in the field of the surface charge of the ionic crystal resulted in an excess "superthermal" vibrationrotation excitation of molecules sublimated from a crystal open surface [2].…”

“…Knudsen mode. In the mass spectra of vapor above gadolinium and terbium tribromides (Table 1) in the temperature ranges 878-1044 and 860-1067 K, respectively, similarly to other tribromides [1][2][3][4][5][6]9], the following ions were identified: Ln + , LnBr + , LnBr . Except for the enumerated ions, two-charge ions Ln ++ , LnBr ++ , and LnBr 2 ++ making a ~3% contribution to the total ionic current were recorded.…”

“…On the basis of relative intensities of ionic currents measured in two sublimation modes, we have estimated the ratio of partial sublimation coefficients α s (LnBr 3 )/α s (Ln 2 Br 6 ) for the studied tribromides at factors 15.7 (GdBr 3 ) and 2.2 (TbBr 3 ). We note that of all studied tribromides [1][2][3][4][5][6] the greatest decrease in the fraction of dimers is observed for GdBr 3 on passing from Knudsen mode to Langmuir mode.…”

“…The systematic study of thermodynamics and kinetics of the molecular and ionic sublimation of tribromide of certain lanthanides was started in [1][2][3][4][5][6].…”