Atomization Enthalpies of the Molecules Cu₃, Ag₃, and Au₃

The gaseous species in equilibrium with Cu(l), Ag(l), and Au(l) were investigated by vaporization studies according to the method of high temperature mass spectrometry with a Knudsen cell. From the observed ion intensity ratios of dimer to monomer and of trimer to monomer the dissociation enthalpies of Cu 2 , Ag 2 , and Au 2 were redetermined. The following atomization and sublimation enthalpies for the trimer in kJ mol −1 could be additionally determined by assuming a linear structure for these molecules: D 0 0 (Cu 3 ) = 294 ± 13, D 0 0 (Ag 3 ) = 253 ± 13, D 0 0 (Au 3 ) = 367 ± 13, δ sub H 0 0 (Cu 3 ) = 714 ± 13, δ sub H 0 0 (Ag 3 ) = 598 ± 12, and δ sub H 0 0 (Au 3 ) = 737 ± 13. At the mean temperature of the measurements of 1849 K (Cu), 1500 K (Ag), and 1883 K (Au) the vapour pressures of the trimers are by a factor of 2.4 · 10 7 (Cu 3 ), 2.9 · 10 7 (Ag 3 ), and 1.7 · 10 7 (Au 3 ) smaller than those of the corresponding monomers.