For solvated PFOS, we observe different C-F bond dissociation timescales ranging from femtoseconds to a few picoseconds. These observations indicate that the dissociation dynamics of each trajectory is unique and differs significantly from the solvated PFOA system. In solvated PFOS, the cavity of the hydrated electron is more compact and is strongly bound by water molecules (see g(r) and number integrals in Figure ), making it less reactive towards the PFOS molecule. For these cases, the hydrated electron preferentially attacks either the C3 (trajectories 02 and 03) or C4 (trajectories 01 and 05) sites in the center of the molecule. Recent static DFT calculations have shown that the sulfonic functional group in PFOS causes the C3 and C4 centers to have the lowest bond dissociation energy among all the C-F bonds, resulting in a markedly different degradation process compared to PFOA. We also compared C-F bond dissociation dynamics between our hydrated vs. excess electron simulations. In the Supporting Information, Figure depicts the dissociation dynamics as a function of time for an excess electron in solvated PFOA (Figure ) and PFOS (Figure ). For solvated PFOA with an excess electron, 12 out of 13 trajectories show C-F bond dissociation timescales less than 100 fs. In contrast, only one trajectory shows a C-F bond dissociation on a longer timescale (around 500 fs). For solvated PFOS, 8 out of 12 trajectories dissociate within a few femtoseconds, whereas four trajectories dissociate on a picosecond timescale. As such, our AIMD simulations suggest that the reaction dynamics of PFASs with hydrated electrons significantly differs from that of an excess electron. The faster C-F bond dissociation in the latter occurs because the spin density is artificially delocalized over the PFAS molecule at the beginning of the simulation. In contrast, for the hydrated electron, the spin density first polarizes the surrounding water molecules.