Atomization energies and heats of formation of gaseous Au2, Tb2, TbAu, HoAu, TbAu2, and HoAu2

Abstract

By means of Knudsen effusion mass spectrometric studies the atomization energies, D°0(kcal mol−1), and standard heats of formation, ΔH°f,298(kcal mol−1), respectively, were obtained for the following: Au2(52.9±0.5, 122.0±1.0), Tb2(30.5±6.0, 155.2±7.0), TbAu(69.2±8.0, 110.5±10), HoAu(63.0±8.0, 96.0±8.7), TbAu2(139.1±10, 128.0±11) and HoAu2(127.3±10, 100.6±10). These data were deduced from a critical assessment of the enthalpy changes of the reactions M2(g)=2M(g) and M(s,1)+M(g)=M2(g) for gold and terbium, and of the reactions LnAu(g)=Ln(g) + Au(g), LnAu(g)+Au(g)=Ln(g)+Au2(g), LnAu2(g)=Ln(g)+2Au(g) and LnAu2(g)+2Au(g)=Ln(g)+2Au2(g) for terbium and holmium. The cited standard heats of formation incorporate appropriate literature data as well as the measured reaction enthalpies. The Pauling model of a polar bond has been used for the interpretation of the measured atomization energies of the Ln–Au molecules and for predicting the dissociation energies of selected intermetallic compounds of terbium.