The ground-state potential energy surface of the ArI2 van der Waals complex is evaluated by means of improved diatomics-in-molecule perturbation theory which provides accurate description of the I2 molecular electronic wave functions taking into account intramolecular nonadiabatic and spin-orbit interactions. A comparison of various DIM models parametrized by different input data reveals an important effect of the nonadi-abatic interaction and a less pronounced effect of the spin-orbit coupling on the topology of the potential, in particular, on the relative depths of the minima in the T-shaped and linear configurations of the complex. The resulting potentials are used to calculate the rovibrational energy levels and estimate the partition functions of two isomers in order to analyze the source of inconsistency in the available experimental data.

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