@article{TEXTUAL,
      recid = {13499},
      author = {Calio, Paul B. and Li, Chenghan and Voth, Gregory A.},
      title = {Resolving the Structural Debate for the Hydrated Excess  Proton in Water},
      journal = {Journal of the American Chemical Society},
      address = {2021-11-01},
      number = {TEXTUAL},
      abstract = {It has long been proposed that the hydrated excess proton  in water (aka the solvated "hydronium" cation) likely has  two limiting forms, that of the Eigen cation  (H<sub>9</sub>O4<sup>+</sup>) and that of the Zundel cation  (H<sub>5</sub>O<sub>2</sub><sup>+</sup>). There has been  debate over which of these two is the more dominant species  and/or whether intermediate (or "distorted") structures  between these two limits are the more realistic  representation. Spectroscopy experiments have recently  provided further results regarding the excess proton. These  experiments show that the hydrated proton has an anisotropy  reorientation time scale on the order of 1-2 ps. This time  scale has been suggested to possibly contradict the picture  of the more rapid "special pair dance" phenomenon for the  hydrated excess proton, which is a signature of a distorted  Eigen cation. The special pair dance was predicted from  prior computational studies in which the hydrated central  core hydronium structure continually switches (O–H···O)*  special pair hydrogen-bond partners with the closest three  water molecules, yielding on average a distorted Eigen  cation with three equivalent and dynamically exchanging  distortions. Through state-of-art simulations it is shown  here that anisotropy reorientation time scales of the same  magnitude are obtained that also include structural  reorientations associated with the special pair dance,  leading to a reinterpretation of the experimental results.  These results and additional analyses point to a distorted  and dynamic Eigen cation as the most prevalent hydrated  proton species in aqueous acid solutions of dilute to  moderate concentration, as opposed to a stabilized or a  distorted (but not "dancing") Zundel cation.},
      url = {http://knowledge.uchicago.edu/record/13499},
}