The Excess Proton at the Air-Water Interface: The Role of Instantaneous Liquid Interfaces

Abstract

The magnitude of the pH of the surface of water continues to be a contentious topic in the physical chemistry of aqueous interfaces. Recent theoretical studies have shown little or no preference for the proton to be at the surface compared to the bulk\cite{baer2014toward}. Using ab-initio molecular dynamics simulations, we revisit the propensity of the excess proton for the air-water interface with a particular focus on the role of instantaneous liquid interfaces. We find a much a stronger propensity of the proton for the surface of water. The enhanced water structuring around the proton results in the presence of proton wires that run parallel to the surface as well as a hydrophobic environment made up of under-coordinated topological defect water molecules, both of which create favorable conditions for proton confinement at the surface. The Grotthuss mechanism within the structured water layer involves a mixture of both concerted and closely spaced stepwise proton hops. The proton makes excursions within the first solvation layer either in proximity to or along the instantaneous interface.

References in corpus (6)

• Canonical sampling through velocity-rescaling
• Perspective: How good is DFT for water?
• A molecular perspective of water at metal interfaces
• Structure and Dynamics of the Instantaneous Water/Vapor Interface Revisited by Path-Integral and Ab-Initio Molecular Dynamics Simulations
• Probing defects and correlations in the hydrogen-bond network of ab initio water
• Surface Tension of Ab Initio Liquid Water at the Water-Air Interface

Cited by in corpus (7)

• Why does hydronium diffuse faster than hydroxide in liquid water?
• Charge Transfer as a Ubiquitous Mechanism in Determining the Negative Charge at Hydrophobic Interfaces
• Correlated Dynamics in Aqueous Proton Diffusion
• First-passage Fingerprints of Water Diffusion near Glutamine Surfaces
• Hierarchical Lattice Models of Hydrogen Bond Networks in Water
• Revisiting the Thickness of the Air-Water Interface from Two Extremes of Interface Hydrogen Bond Dynamics
• Automated detection of many-particle solvation states for accurate characterizations of diffusion kinetics