The ArH emission at 7670 Å first observed by Johns in 1970, is produced by X-ray irradiation of Ar gas mixtures with H2, H2O, CH4 or CH3OH. To assign this transition, potential curves for the Rydberg states of ArH+ converging to the ground state of ArH+ are calculated by a fast method, whereby Hartree-Fock electron affinities of ArH+. are added to the ArH+ potential. Results with and without semi-empirical correlation corrections are presented. The 7670 /rA transition is shown to be G 2Π → A 2Σ with the lower state predissociated by vibronic interaction with the continuum of the ArH around state.