Figure shows the potential energy curves of the minimum energy path (𝑉 )*+ in solid curve) and the vibrationally adiabatic ground-state energy curves (𝑉 , -in dotted curve), which include the zero-point energies along the mass-scaled reaction coordinate (s) for two extreme cases i.e., 1H,H and 5CF3,CF3. First, from the plots, it can be seen that no stable intermediates were observed in the potential and adiabatic energy curves along the reaction coordinate, which indicates that the three hydrogens in the two-water bridged tautomerization were transferred concertedly. Second and most interestingly, the broadness (round top and flatten section) of the 𝑉 )*+ and 𝑉 , -curve around the TS region is evident for 5CF3,CF3 as compared to 1H,H, which exhibit a higher but narrow barrier shape ideal for swift tunneling. This observation thus indicates that a high barrier possesses a more sharply rising or narrow potential and adiabatic energy curves, resulting in an expected large kT.