New high-level ab initio calculations for ArI and ArI₂ are reported and compared with experiments. For the directly calculated PES, the D₀ values for both linear (L) and T-shaped conformers of ArI₂ are found to be significantly larger (D₀(L) = 197 and D₀(T) = 181 cm^-1) than deduced from recent experimental data. A further DIM-based correction in term of empirical diatomic potentials is successfully tested for ArCl₂ and predicts for ArI₂ the intervals D₀(L) = 250±8 and D₀(T) = 242±11 cm^-1, matching earlier experimental results.