Dissociation energies of the intermetallic molecules CuIn, AgIn, and AuIn

The gaseous diatomic intermetallic molecules of the IA-IIIB groups, elements CuIn, AgIn, and AuIn, were investigated in a Knudsen cell-mass spectrometric study of the vapors over the respective alloys. From a number of all-gas equilibria their dissociation energies have been derived: Do0(CuIn) =183.7±7.9, Do0(AgIn) =162.8±4.9, Do0(AuIn) =282.3±5.7 kJ/mol. These values were compared to the values calculated from empirical models of bond. Of particular interest is the strikingly high dissociation energy of AuIn which was interpreted in terms of relativistic effects rather than due to multiple bond. The implications in the indium electronegativity value and the mode of formation of AuIn(g) are also discussed.