The excess electron then begins to shrink, further polarizing the PFAS molecule, until the spin density slowly accumulates at the dissociation site. To compare these different PFAS decomposition mechanisms, we calculated C-F bond distances for our pre-created cavity simulations for the hydrated electron (Figure ). Four dissociation starts within 1.00 ps in solvated PFOA). Among the various CF 2 groups along the PFOA backbone, we observe defluorination at the α-position for trajectories 02 and 03. Previous studies have suggested two major reaction pathways for PFOA degradation with hydrated electrons, including H/F exchange and chain shortening. Among the different chemical functional groups present in PFOA, the -CF 2 -group at the α-position has a high reactivity due to the inductive effect of the head group, resulting in reactions at this preferred region. Indeed, DFT calculations have shown that the simple addition of an excess charge to the PFOA molecule results in spontaneous stretching of C-F bonds at the α-position, facilitating their cleavage. However, the same studies also proposed that C-F bonds in the middle of the carbon chain can also be cleaved. Therefore, although the α C-F bond is thermodynamically more reactive, all of the other C-F bonds also have a high probability (whose statistics are explored by our first-principles MD simulations) to dissociate.