Deciphering the infrared spectrum of the hydrated proton using full-dimensional quantum dynamics

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• The aqueous proton's structure is traditionally described by Zundel and Eigen cation models.
• Experimental IR spectra reveal dynamic characteristics and intensity modulations in the proton's absorption band.
• Ultrafast spectroscopy indicates solvation-induced distortions significantly influence the IR response of H2O⋯H+⋯OH2 motifs.

Purpose of the Study:

• To investigate the role of asymmetry in solvation shells on the aqueous proton's structure and dynamics.
• To establish a link between solvation environment asymmetry and spectral features.
• To provide a structural and dynamical basis for understanding proton mobility in water.

Main Methods:

• Full-dimensional quantum dynamics simulations were performed on the extended Zundel complex H+(H2O)6.
• Systematic removal of water molecules from the second solvation shell was employed to induce asymmetry.
• Analysis focused on the structural response and spectral features of the aqueous proton.

Main Results:

• Simulations show that deviations from a symmetric Zundel-like complex lead to Eigen-like spectral features.
• A direct correlation was mapped between asymmetric solvation and the structural response of the first and second solvation shells.
• The study highlights how solvation asymmetry governs the dynamic behavior of the aqueous proton.

Conclusions:

• The aqueous proton exhibits a dynamic character influenced by solvation shell asymmetry.
• Quantum dynamics simulations provide insights into the structural basis of spectral variations.
• Understanding solvation asymmetry is crucial for explaining proton mobility in aqueous systems.