Elucidating Au-C Bonding via Laser Spectroscopy of Gold Monocarbide

Gold monocarbide (AuC) has been produced and characterized using laser spectroscopy, representing the first reported observation of AuC. We recorded the optical spectrum of gas-phase AuC between 400 nm and 700 nm, assigning excitations from the $\mathrm{X}\,^2\Pi_{1/2}( (2\sigma)^2 (2\pi)^1 )$ ground state to states arising from the $(2\sigma)^2 (3\sigma^\ast)^1 $ and $(2\sigma)^1 (2\pi)^2 $ configurations. Dispersed-fluorescence spectra are used to study the vibrational and spin-orbit structure of the ground state, branching ratios and radiative lifetimes of the excited states, and the Au--C bond dissociation energy. A molecular orbital diagram is used to rationalize the nature of AuC's low-lying electronic states. The data serve as valuable benchmarks of relativistic theory and are relevant to quantum science and precision measurements with cold molecules.