We study the hydration of protons in liquid water using terahertz time-domain spectroscopy and polarization-resolved femtosecond midinfrared pump-probe spectroscopy. We observe that the addition of protons leads to a very strong decrease of the dielectric response of liquid water that corresponds to 19±2 water molecules per dissolved proton. This depolarization results from water molecules (∼4) that are irrotationally bound to the proton and from the motion of water (corresponding to the response of ∼15 water molecules) involved in the transfer of the proton charge.

Phys. Rev. Lett.
Ultrafast Spectroscopy

Tielrooij, K. J., Timmer, R., Bakker, H., & Bonn, M. (2009). Structure dynamics of the proton in liquid water probed with terahertz time-domain spectroscopy. Phys.Rev.Lett., 102(Article number: 198303), 1–4. doi:10.1103/physrevlett.102.198303