Knudsen effusion mass spectrometric determination of the complex vapor composition of samarium, europium, and ytterbium bromides

摘要

RATIONALE: The vaporization of Sm, Eu, and Yb tri- and dibromides is accompanied by decomposition and disproportionation reactions. These result in complex vapor compositions whose analysis is an intricate problem for experimentalists. Approaches have been developed to interpret mass spectra and accurately determine the vapor composition of thermally unstable compounds. METHODS: A sector type magnet instrument was used. A combined ion source allowed the study of both the molecular and ionic vapor compositions in the electron ionization (EI) and the thermionic emission (TE) modes. The methodological approaches were based on a joint analysis of the ionization efficiency functions, the temperature and time dependences of the ion currents, and special mathematical data evaluation. RESULTS: The vaporization of SmBr_3, YbBr_3, SmBr_2, EuBr_2, and YbBr_2 was studied in the temperature range of 850-1300 K. An initial stage of incongruent vaporization was observed in the case of the tribromides, SmBr_2, and YbBr_2. This eventually changed to a congruent vaporization stage. Various neutral (Ln, Br, Br_2, LnBr, LnBr_2, LnBr_3, Ln_2Br_4, Ln_2Br_5, and Ln_2Br_6) and charged (Br~-, LnBr_3~-, LnBr_4~-) species were detected at different vaporization stages. CONCLUSIONS: The quantitative vapor composition of Sm, Eu, and Yb tri- and dibromides was determined. It was found that only EuBr_2 was stable in the studied temperature range. The developed approaches can be useful in the case of other thermally unstable compounds.