The potential curves and spectroscopic constants of the excited states of alkali–argon diatomics MRg (M=Li, Na and K, Rg=Ar) are calculated using usual semilocal single valence electron pseudopotentials on alkali atoms $[{\mathrm{M}}^{+}]$ -core pseudopotentials), semilocal pseudopotentials replac(ing all the electrons of argon ([Ar]-core pseudopotentials), and core polarization pseudopotentials on both centers. All states dissociating into $\mathrm{Li}\text{(2s,}$ $\text{2p,}$ $\text{3s,}$ $\text{3p,}$ $\text{3d,}$ $\text{4s,}$ and $\text{4p),}$ $\mathrm{Na}\text{(3s,}$ $\text{3p,}$ $\text{3d,}$ $\text{4s,}$ $\text{4p,}$ $\text{4d,}$ $\text{5p)}$ and $\mathrm{K(4}\mathrm{s}\mathrm{,}$ $\text{4p,}$ $\text{5s,}$ $\text{3d,}$ $\text{5p,}$ $\text{4d,}$ $\text{6s,}$ $\text{4f,}$ $\text{6p,}$ $\text{5d,}$ $\text{7s,}$ $\text{5f)}$ are considered. The core–core interactions for ${\mathrm{Li}}^{+}\mathrm{Ar}$ and ${\mathrm{Na}}^{+}\mathrm{Ar}$ are included using the accurate ab initio potentials of Ahmadi et al. [G. R. Ahmadi, J. Almlöf, and I. Roeggen, Chem. Phys. 199, 33 (1995); G. R. Ahmadi and I. Roeggen, J. Phys. B 27, 5603 (1994)] while the ${\mathrm{K}}^{+}\mathrm{Ar}$ ion data are determined by MP2 all-electron calculations.

Accurate positions and nonradiative lifetimes of states belonging to the adiabatic A state of LiH are estimated. The results coming from a Golden Rule treatment in the adiabatic scheme present excellent agreement with those obtained through a diabatic close coupling calculation. That confirms the accuracy reached in both approaches and also in the treatment of the diabatic–adiabatic transformation. It involves, in particular, an effective phase control that is needed to properly estimate nonadiabatic couplings. Also, a powerful numerical procedure to obtain energy profiles in the diabatic close coupling frame is described and applied in this work.