Given the critical role of the aqueous excess proton in redox chemistry, determining its structure and the mechanism of its transport in water are intense areas of experimental and theoretical research. The ultrafast dynamics of the proton’s hydration structure has made it extremely challenging to study experimentally. Using ultrafast broadband two-dimensional infrared spectroscopy, we show that the vibrational spectrum of the aqueous proton is fully consistent with a protonated water complex broadly defined as a Zundel-like H₅O₂⁺ motif. Analysis of the inhomogeneously broadened proton stretch two-dimensional lineshape indicates an intrinsically asymmetric, low-barrier O–H⁺–O potential that exhibits surprisingly persistent distributions in both its asymmetry and O–O distance. This structural characterization has direct implications for the extent of delocalization exhibited by a proton’s excess charge and for the possible mechanisms of proton transport in water.

鉴于含水过量质子在氧化还原化学中的关键作用，确定其结构及其在水中的传输机理是实验和理论研究的重点领域。质子水化结构的超快动力学使进行实验研究变得极具挑战性。使用超快宽带二维红外光谱，我们显示了质子水溶液的振动光谱与质子化水复合物完全一致，质子化水复合物被广泛定义为Zundel样H ₅ O ₂ ⁺母题。对不均匀加宽的质子拉伸二维线形的分析表明，本征是不对称的，低势垒的O–H ⁺-O势在其不对称性和O-O距离上均表现出令人惊讶的持续分布。这种结构特征对质子过量电荷所表现出的离域化程度以及质子在水中的可能迁移机制具有直接的影响。