Relativistic and correlated all-electron calculations on the ground and excited states of AgH and AuH

We report relativistic all-electron multireference based perturbation calculations on the low-lying excited states of gold and silver hydrides. For AuH, we consider all molecular states dissociating to the $\mathrm{Au}{(}^2\mathrm{S)+}\mathrm{H}{(}^2\mathrm{S)}$ and $\mathrm{Au}{(}^2\mathrm{D)+}\mathrm{H}{(}^2\mathrm{S)}$ atomic limits, and for AgH, the states corresponding to the $\mathrm{Ag}{(}^2\mathrm{S)+}\mathrm{H}{(}^2\mathrm{S),}$ $\mathrm{Ag}{(}^2\mathrm{P)+}\mathrm{H}{(}^2\mathrm{S),}$ and $\mathrm{Ag}{(}^2\mathrm{D)+}\mathrm{H}{(}^2\mathrm{S)}$ dissociation channels. Spin-free relativistic effects and the correlation effects are treated on the same footing through the relativistic scheme of eliminating small components (RESC). Spin–orbit effects are included perturbatively. The calculated potential energy curves for AgH are the first reported in the literature. The computed spectroscopic properties agree well with experimental findings; however, the assignment of states does not correspond to our calculations. Therefore, we give a reinterpretation of the experimentally observed ${\mathrm{C }}^1\mathrm{\Pi ,}$ ${\mathrm{a }}^3\mathrm{\Pi ,}$ ${\mathrm{B }}^1{\Sigma }^{+},$ ${\mathrm{b(}}^3{\Delta }_1\text{)1,}$ ${\mathrm{D }}^1\mathrm{\Pi ,}$ $c_1^3{\Pi }_1,$ and $c_0{(}^3{\Pi }_0)$ states. A labeling suggested by us is $\text{a1,}$ ${\text{C0}}^{+},$ ${\text{b0}}^{-},$ $\text{c2,}$ $B^3{\Pi }_{0^{+}},$ $d^3{\Pi }_1,$ $\text{e1,}$ $\text{f1}$ and $\text{g1,}$ respectively. The spin–orbit states corresponding to $\mathrm{Ag}{(}^2\mathrm{D)+}\mathrm{H}{(}^2\mathrm{S)}$ have not well defined the $\Lambda$ and S quantum numbers, and therefore, they probably correspond to Hund’s coupling case c. For AuH, we present a comparison of the calculated potential energy curves and spectroscopic parameters with the previous configuration interaction study and the experiment.