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Vaporization of Compounds and Alloys at High Temperature. Part 1. Mass Spectrometric Determination of the Dissociation Energies of the Molecules AgAu, AgCu, and AuCu

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The vapors issuing from mullite and Grpahite 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 Cu2 43.2 or - 2.2 kcal AgAu 47.6 or - 2.2 kcal Ag2 35.7 or - 2.2 kcal AgCu 40.7 or - 2.2 kcal Au2 51.9 or - 2.2 kcal AuCu 54.3 or -2.2 kcal. These are based on H sup vap sub 298 81.1, 68.4 and 87.5 calmole for Cu, Ag and Au where dissociation energy of AgAu depends on the value for Cu, and dissociation energy of AgAu and AuCu on Au. The uncertainties quoted do not include the uncertainty in Delta H sup vap. These results are interpreted in terms of chemical bonding theories. The relation between bonding in the gas and in the pure condensed phases is again observed. Furthermore, a previously unobserved qualitative relation between the dissociation energy of the asymmetrical molecule and the heat of formation of the corresponding alloys is indicated.

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  • Physical Chemistry

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