The structure and energetics of the ArnO- clusters for n=1,...,13 have been modeled in the framework of Diffusion Monte Carlo (DMC), using two- and three-body ab initio determined potentials derived previously by Buchachenko [J. Chem. Phys. 112, 5852 (2000)], and Jakowski [preceding paper, J. Chem. Phys. 118, 2731 (2003)], respectively. The anion cluster structures are largely determined by the two-body potential since the dominant contribution to the stabilization energy is due to pair interactions. However, the three-body effects are important since their role grows with n, from a few percent for n=2 to ca. 30% for n=12. The three-body effects are well approximated by the induction component only. The exchange and dispersion three-body and the induction many-body effects were found to be much less important. The effect of the spin-orbit coupling on the stabilization energies is small and almost independent of the size of a cluster. Specifically, it amounts to about 5% for ArO-, and to 0.1% for Ar12O-. The ab initio cluster stabilization energies are compared with those derived from the experimental measurements of electron detachment energies. The agreement is qualitatively good, and the origins of quantitative discrepancies are discussed. (C) 2003 American Institute of Physics.