Gaseous Metal Borides. III. The Dissociation Energy and Heat of Formation of Gold Monoboride

Abstract

The AuB molecule has been identified in the vapor phase over an Au–BN–C mixture and an Au–Ce–CeS–BN–C mixture, using a combination of Knudsen effusion and mass spectrometric techniques. Its appearance potential was measured as 8.7 ± 0.5 eV. The enthalpies for the reactions AuB(g)+Au(g)=Au2(g)+B(g), AuB(g)+Ce(g)=CeAu(g)+B(g), and AuB(g)=Au(g)+B(g) were determined by the second and third law method. Combined with published ancillary data these reaction enthalpies yielded the following thermodynamic properties for gaseous AuB: AuB(g)=Au(g)+B(g), D0° = 87.0 ± 2.5 kcal mol−1 or 364 ± 11 kJ mol−1; Au(s)+B(c)=AuB(g), ΔHf,298° = 135.3 ± 3.0 kcal mol−1or 566 ± 13 kJ mol−1.