Characterization of Vibrational Resonances of Water-Vapor Interfaces by Phase-Sensitive Sum-Frequency Spectroscopy

Abstract

Phase-sensitive sum-frequency spectroscopy provides correct characterization of vibrational resonances of water-vapor interfaces and allows better identification of interfacial water species contributing to different parts of the spectra. Iodine ions emerging at an interface create a surface field that tends to reorient the more loosely bonded water molecules below the topmost layer.

Interfacial Structures of Acidic and Basic Aqueous Solutions

“…To facilitate the discussion, therefore, we need to briefly review the spectra and structure of the neat water/vapor interface deduced from our earlier PS-SFVS measurement. 22 We have found that while the We now compare the spectra of water/vapor interfaces of aqueous solutions with those of neat water. The spectral change then allows us to learn how ions emerging at the interfaces perturb the interfacial structure.…”

“…From previous SFVS studies of NaI solution, 22 it is known that I -ions prefer to come to the surface and create a negative surface field. The spectral change with respect to the neat water interface mainly comes from the surface field reorienting the interfacial DDAA water molecules.…”

“…The spectral change with respect to the neat water interface mainly comes from the surface field reorienting the interfacial DDAA water molecules. 22 On the other hand, in HCl solution, the surface field created by excess H + is positive and induces a spectral change opposite to that in NaI solution. Thus if we choose a proper linear combination of the two spectra for HCl and NaI solutions, we can expect cancellation of the surface field effect in the combined spectrum.…”

“…22 We can now use the neat water/vapor interface as a reference in our SFVS study of water/vapor interfaces of acid and base solutions. From the spectral changes resulting from dissolving acid or base into water, we can learn how various types of ions appearing at the interface can perturb the interfacial water structure.…”

Revealing structural properties of the marine nanolayer from vibrational sum frequency generation spectra

“…An alternative interpretation, which is subject to ongoing scientific discussion Shen, 2008, 2009], assigns the whole band to a Fermi resonance resulting from an intramolecular coupling of a stretch vibration with a bending mode overtone vibration of water [Sovago et al, 2008]. Very recently, stimulated by new experimental results of a phase-sensitive VSFG study [Ji et al, 2008], Fan et al [2009] presented yet another interpretation based on molecular dynamics calculations. According to their consistent two-layer model of interfacial water, the broad spectral feature is made up of four distinct types of hydrogen bond stretches peaking at 3117 cm −1 ("upward" pointing OH in layer II, ice like), 3222 cm −1 ("downward" pointing OH in layer I, ice like), 3448 cm −1 (downward pointing OH in layer II, liquid like), and 3696 cm −1 (upward pointing OH in layer I, dangling OH).…”