Dissociation Energies of Cu2, Ag2, and Au2

Abstract

A combination of a Knudsen cell and mass spectrometric analysis of the effusing vapor has been used to study the gaseous species in equilibrium with Cu(l), Ag(l), and Au(l). From the observed ratios of monomer to dimer the following dissociation energies have been calculated $$\begin{array}{c}{D}_0^0({\mathrm{Cu}}_2\text{)=2.21±0.11\hspace{0.17em}}\mathrm{ev},\\ D_0^0({\mathrm{Ag}}_2\text{)=1.78±0.10\hspace{0.17em}}\mathrm{ev},\\ D_0^0({\mathrm{Au}}_2\text{)=2.30±0.12\hspace{0.17em}}\mathrm{ev}.\end{array}$$ Upper limits for the abundances of the trimers and tetramers are given. Combining the vapor pressure ratios with accepted values for the heats of sublimation of the monomers, the following heats of sublimation for the dimers at 0°K are obtained. $$\begin{array}{c}\mathrm{L(}{\mathrm{Cu}}_2\text{)=110±4\hspace{0.17em}}\mathrm{kcal},\\ \mathrm{L(}{\mathrm{Ag}}_2\text{)=\hspace{0.17em}95±4\hspace{0.17em}}\mathrm{kcal},\\ \mathrm{L(}{\mathrm{Au}}_2\text{)=118±5\hspace{0.17em}}\mathrm{kcal}.\end{array}$$