MASS SPECTROMETRIC STUDIES AT HIGH TEMPERATURES .25. VAPOR COMPOSITION OVER LACL3 EUCL3 AND LUCL3 AND STABILITIES OF TRICHLORIDE DIMERS

Mass spectrometric studies of the vapors over LaCl3(s), EuC13(S), EuCl2(l) and the mixture EuCl3 + LuCl3 indicate the existence of dimers in small amount (1%) at pressures of less than 0.1 mm. However, the data predict dimers to be a more dominant species at temperatures approaching the boiling point. Ion current vs. temperature data yield heats of vaporization or sublimation that are in good agreement with previous results as well as values for the heats of dimerization. With absolute pressure data, one calculates the entropy for the reaction 2LaCl3(g) = La2Cl6(g) to be ΔS °1000 °K = -30.0 ± 3.0 e.u./mole of dimer. The proportion of dimer to monomer, as indicated by the heats of dimerization, varies considerably with the nature of the metal. No dimerization or significant disproportionation of EuCl2(g) was found. © 1968.