Au-S Bonding Revealed from the Characterization of Diatomic Gold Sulfide, AuS.

Gold monosulfide, AuS, has been detected and characterized in the gas phase using optical spectroscopy. The symmetries of the ground and low-lying electronic excited states have been determined by application of a synergy of hot and cold laser excitation techniques. The electronic spectra are assigned to progressions in four band systems associated with excitations from the X(2)Πi ((2σ)(2)(2π)(3)) ground state to the A(2)Σ(+) state arising from the (2σ)(1)(2π)(4) configuration and to the a(4)Σ(-), B(2)Σ(-), and C(2)Δi states arising from the (2σ)(2)(2π)(2)(3σ*)(1) configuration. The bond length and dissociation energy of the ground X(2)Πi state are determined to be 2.156(2) Å and 298 ± 2 kJ/mol, respectively. A molecular orbital correlation diagram is used to rationalize the energy ordering of the excited states and the associated harmonic frequencies.