The uncertain bond energy of the NaAu molecule: experimental redetermination and coupled cluster calculations

The dissociation energy of the intermetallic molecule NaAu, for which two largely at variance experimental values are available in the literature, has been redetermined by the Knudsen effusion mass spectrometry method. The molecule has been produced in the vapor phase by a specially designed experimental setting inspired by the double oven technique. The equilibrium of dissociation to atoms as well as the exchange equilibrium with the gold dimer were monitored mass-spectrometrically over about a 600 K temperature range. The third-law analysis of the equilibrium data provides the dissociation energy D0° (NaAu, g) = 245.3 ± 6.8 kJ/mol, corresponding to a formation enthalpy at 298 K of 228.3 ± 7.5 kJ/mol. The NaAu species was also studied computationally at the CCSD(T) level with basis sets of increasing zeta quality thus allowing to evaluate the molecular parameters and the dissociation energy at the complete basis set limit.