Finally, we computed TD-DFT absorption spectra along the MP2 geometry relaxation pathways that were discussed above, in order to observe how gradual spinlocalization affects the UV spectrum; see Fig. . As in the dimer and pentamer models, the most intense transition remains the 1b 2 (H 2 O) → 2p( OH) charge-transfer transition, even for O * • • • O distances large enough to engender complete spin localization. (Representative attachment and detachment densities for this chargetransfer transition are shown in Fig. .) Although the intensity of this feature is reduced as the spin localizes onto the OH moiety, spectra computed at nonhemibonded configurations do not exhibit any comparable transition in the region where the experimental λ max for OH(aq) appears; see Fig. .