This work activation energy. The extent to which tunneling occurs in a chemical reaction can be approximated as 𝑃~𝑒 !" # ∆% ‡ &/ℏ (where 𝑃 represents the probability of tunneling, w the barrier width, ∆E ‡ is the activation energy, m the reduced mass, and ℏ the reduced Planck constant). Tautomerization plays a vital role in chemistry and biology and proton tunneling has been well-established in such processes. Water as a catalyst in tautomerization reactions, and the influence of tunneling in them, have been documented.