Study of the Vapour of the Cr ‐ Ge, Cr ‐ Sn, and Cr ‐ Pb Systems: Vapour Composition and Dissociation Energy of the Intermetallic Molecules CrGe, CrGe2, CrSn, and CrPb

Abstract

AbstractThe equilibrium vapour of the systems Cr ‐ Ge, Cr ‐ Sn, and Cr ‐ Pb was investigated by using Knudsen effusion mass spectrometry in the temperature ranges of 1609 ‐ 1808 K, 1409 ‐ 1641 K, and 1526 ‐ 1745 K, respectively. The gaseous heteronuclear diatomic species CrM (M = Ge, Sn, Pb) were observed in each case in addition to the species Cr, Cr2, Gen, (n = 1 – 9), Sn, (i = 1–5), and Pb, (j = 1 – 4). CrGe2 was the only heteronuclear species detected as being larger than the dimer. The appearance potentials of the ions CrGe+ and CrSn+ were determined by ionization efficiency measurements as 6.71 ± 0.02 and 6.31 ± 0.02 V, respectively. The enthalpy changes of the following dissociation and pressure‐independent isomolecular exchange reactions were evaluated according to the second‐ and third‐law methods: equation image The enthalpy of dissociation of the dimer M2 obtained in this work agrees excellently with the values from the literature thereby demonstrating the accuracy of the measurements. The following enthalpies of dissociation and bond energies result for the diatomic heteronuclear species and for CrGe2 in kJ mol−1: equation image The different values are discussed.