Comment on "Orientational Distribution of Free O-H Groups of Interfacial Water is Exponential"

TL;DR

This paper critically examines a recent study claiming an exponential orientational distribution of free O-H groups at the water interface, arguing that its data interpretation is flawed and contradicts established literature.

Contribution

It provides a critical analysis challenging the original interpretation of SFG-VS data regarding interfacial water orientation.

Findings

Original conclusions are based on questionable data interpretation.

Contradicts established literature on water interfacial structure.

Highlights the need for careful data analysis in SFG-VS studies.

Abstract

In a recent letter (PRL,121,246101,2018), Sun et al. reported that combined MD simulation and sum frequency generation vibrational spectroscopy (SFG-VS) measurements led to conclusions of a broad and exponentially decaying orientational distribution, and the presence of the free O-H group pointing down to the bulk at the air/water interface. In this comment, we show that their main conclusions are based on questionable interpretation of the SFG-VS data presented in the letter [1], and are also contrary to the established data analysis and interpretations in the literature [2-5].