2005/06/16 by Jeffrey M. Headrick, Eric G. Diken, R. Walters +7 · 2 citations
Physics and Astronomy · Chemistry · #Spectroscopy and Quantum Chemical Studies #Advanced Chemical Physics Studies #Molecular Spectroscopy and Structure
paper · doi:10.1126/science.1113094
openalex publication_date 2005/06/16 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
The ease with which the pH of water is measured obscures the fact that there is presently no clear molecular description for the hydrated proton. The mid-infrared spectrum of bulk aqueous acid, for example, is too diffuse to establish the roles of the putative Eigen (H3O+) and Zundel (H5O2+) ion cores. To expose the local environment of the excess charge, we report how the vibrational spectrum of protonated water clusters evolves in the size range from 2 to 11 water molecules. Signature bands indicating embedded Eigen or Zundel limiting forms are observed in all of the spectra with the exception of the three- and five-membered clusters. These unique species display bands appearing at intermediate energies, reflecting asymmetric solvation of the core ion. Taken together, the data reveal the pronounced spectral impact of subtle changes in the hydration environment.