The Structure of the Hydrogen Ion (Haq+) in Water

The hydrogen ion in water, H-aq(+), is a unique H13O6+ entity that defines the boundary of positive-charge delocalization. Its central unit is neither a C-3 nu H3O+ Eigen-type ion nor a typical H5O2+ Zundel-type ion. IR spectroscopy indicates that the H13O6+ ion has an unexpectedly long central O center dot center dot center dot O separation (>> 2.43 angstrom), showing that in comparison with the gas and solid phases, the environment of liquid water is uniquely proficient in delocalizing positive charge. These results will change the description of H-aq(+) in textbooks of chemistry, and a more extensive delocalization of positive charge may need to be incorporated into descriptions of mechanisms of aqueous proton transport.