A possible explanation for the apparently anomalous behavior of ClO - 3 can be found by examining radial distribution functions (RDFs), g(r), obtained from the MD simulations. (These can be found in the Supporting Information for Ref. 7 but the salient details are described here.) Amongst the chlorine oxyanions, a unique feature of ClO - 3 is the appearance of two distinct peaks in the RDF for Cl• • • O w (where O w denotes water oxygen), one at r ≈ 3.5 Å and another at r ≈ 4.1 Å. For each of the other ClO - n species, the RDF consists of a single well-resolved feature at r ≈ 3.5-3.7 Å. The shorter-r feature for ClO - 3 does not appear to be present in simulations based on a hybrid quantum mechanics/molecular mechanics (QM/MM) formalism, which were used to interpret x-ray scattering results . If the small-r feature for ClO - 3 is an indication of an extraneous water molecule present at short range, then this could explain the anomalously repulsive values of E elst+exch that we then compute at snapshots extracted from the MD simulations. The presence of such a water molecule in those simulations, however, suggests that something in AMOEBA's ion-water interaction is compensating for the short-range repulsion, or perhaps that the latter is simply not repulsive enough. Although polyvalent anions are not considered in the present work (because they are excluded from the air/water interface), it is notable that a short-r peak in the S• • • O w RDF is also observed in the simulations of SO 2- 3 (aq) that were reported in Ref. 7. These feature also appears to be absent from QM/MM simulations and x-ray scattering experiments . In view of this, AMOEBA parameterizations for both of these ions ought to be revisited. This is beyond the scope of the present work, though it is interesting to note the way that SAPT analysis of ion-water clusters was able to detect an anomaly. Notably, vertical ionization energies computed for ClO - 3 (aq) and SO 2- 3 (aq) in Ref. 7 are no less accurate, as compared to experimental values , than what we obtain for other inorganic anions including other ClO - n ions . The typical accuracy reported in Ref. 7 is ∼ 0.2 eV, considerably smaller than the widths of the corresponding photoelectron spectra.