Details

Autor(en) / Beteiligte

• Carpenter, William B.
• Yu, Qi
• Hack, John H.
• Dereka, Bogdan
• Bowman, Joel M.
• Tokmakoff, Andrei

Titel

Decoding the 2D IR spectrum of the aqueous proton with high-level VSCF/VCI calculations

Ist Teil von

• The Journal of chemical physics, 2020-09, Vol.153 (12), p.124506-124506

Ort / Verlag

Melville: American Institute of Physics

Erscheinungsjahr

2020

Quelle

AIP Journals (American Institute of Physics)

Beschreibungen/Notizen

• The aqueous proton is a common and long-studied species in chemistry, yet there is currently intense interest devoted to understanding its hydration structure and transport dynamics. Typically described in terms of two limiting structures observed in gas-phase clusters, the Zundel H5O2+ and Eigen H9O4+ ions, the aqueous structure is less clear due to the heterogeneity of hydrogen bonding environments and room-temperature structural fluctuations in water. The linear infrared (IR) spectrum, which reports on structural configurations, is challenging to interpret because it appears as a continuum of absorption, and the underlying vibrational modes are strongly anharmonically coupled to each other. Recent two-dimensional IR (2D IR) experiments presented strong evidence for asymmetric Zundel-like motifs in solution, but true structure–spectrum correlations are missing and complicated by the anharmonicity of the system. In this study, we employ high-level vibrational self-consistent field/virtual state configuration interaction calculations to demonstrate that the 2D IR spectrum reports on a broad distribution of geometric configurations of the aqueous proton. We find that the diagonal 2D IR spectrum around 1200 cm−1 is dominated by the proton stretch vibrations of Zundel-like and intermediate geometries, broadened by the heterogeneity of aqueous configurations. There is a wide distribution of multidimensional potential shapes for the proton stretching vibration with varying degrees of potential asymmetry and confinement. Finally, we find specific cross peak patterns due to aqueous Zundel-like species. These studies provide clarity on highly debated spectral assignments and stringent spectroscopic benchmarks for future simulations.