Mass Spectrometric Determination of the Dissociation Energies of the Molecules AgAu, AgCu, and AuCu

The vapors issuing from mullite and graphite Knudsen cells containing pure metals and alloys of the triad Cu–Ag–Au have been analyzed mass spectrometrically. From the experimental ratios of diatomic to monoatomic species and the vapor pressures of the elements, the following dissociation energies are obtained: D00(Cu2)=45.5±2.2 kcalD00(AgAu)=47.6±2.2 kcalD00(Ag2)=37.6±2.2 kcalD00(AgCu)=40.7±2.2 kcalD00(Au2)=51.5±2.2 kcalD00(AuCu)=54.5±2.2 kcalThese are based on ΔH298vap=81.1, 68.4, and 87.5 kcal/g-atom for Cu, Ag, and Au where D00 of AgCu depends on the value for Cu, and D00 of AgAu and AuCu on Au. The uncertainties quoted do not include the uncertainty in ΔHvap.