Ab initio many-electron study for the low-lying states of the alkali hydride cations in the adiabatic representation Theoretical calculation of the excited states of the KCs molecule including the spin-orbit interactionThe potential curves and spectroscopic constants of the excited states of alkali-argon diatomics MRg ͑MϭLi, Na and K, RgϭAr͒ are calculated using usual semilocal single valence electron pseudopotentials on alkali atoms ͓͑M ϩ ͔-core pseudopotentials͒, semilocal pseudopotentials replacing all the electrons of argon ͓͑Ar͔-core pseudopotentials͒, and core polarization pseudopotentials on both centers. All states dissociating into Li͑2s, 2p, 3s, 3p, 3d, 4s, and 4p͒, Na͑3s, 3p, 3d, 4s, 4p, 4d, 5p͒ and K͑4s, 4p, 5s, 3d, 5p, 4d, 6s, 4f , 6p, 5d, 7s, 5f ͒ are considered. The core-core interactions for Li ϩ Ar and Na ϩ 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 ͑1995͒; G. R. Ahmadi and I. Roeggen, J. Phys. B 27, 5603 ͑1994͔͒ while the K ϩ Ar ion data are determined by MP2 all-electron calculations.