Solvated electrons at the water–air interface: surface versus bulk signal in low kinetic energy photoelectron spectroscopy

Buchner, Franziska; Schultz, Thomas; Lübcke, A.

doi:10.1039/c2cp23305c

Cited by 65 publications

(112 citation statements)

References 44 publications

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“…This view is consistent with the fact that negative ζ-potentials of colloidal drops and bubbles in the static electric fields of electrophoretic experiments require the presence of negatively charged discrete entities that can migrate independently of their counterions, such as OH − , rather than of inward-pointing water dipoles or chargetransfer [H 2 O − ···H 2 O + ] moieties (55)(56)(57)(58). A potential role for hydrated electrons, H 2 O·e − , as discrete carriers can be discarded because their formation via 3 H 2 O = H 2 O·e − + H 3 O + + ·OH, is thermodynamically forbidden under ambient conditions (56,59,60).…”

Section: Quantum-mechanical Calculationsmentioning

confidence: 99%

Brønsted basicity of the air–water interface

Mishra

Enami

Nielsen

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

172

203

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Differences in the extent of protonation of functional groups lying on either side of water-hydrophobe interfaces are deemed essential to enzymatic catalysis, molecular recognition, bioenergetic transduction, and atmospheric aerosol-gas exchanges. The sign and range of such differences, however, remain conjectural. Herein we report experiments showing that gaseous carboxylic acids RCOOH(g) begin to deprotonate on the surface of water significantly more acidic than that supporting the dissociation of dissolved acids RCOOH(aq). Thermodynamic analysis indicates that > 6 H 2 O molecules must participate in the deprotonation of RCOOH(g) on water, but quantum mechanical calculations on a model air-water interface predict that such event is hindered by a significant kinetic barrier unless OH − ions are present therein. Thus, by detecting RCOO − we demonstrate the presence of OH − on the aerial side of on pH > 2 water exposed to RCOOH(g). Furthermore, because in similar experiments the base (Me) 3 N(g) is protonated only on pH < 4 water, we infer that the outer surface of water is Brønsted neutral at pH ∼3 (rather than at pH 7 as bulk water), a value that matches the isoelectric point of bubbles and oil droplets in independent electrophoretic experiments. The OH − densities sensed by RCOOH(g) on the aerial surface of water, however, are considerably smaller than those at the (>1 nm) deeper shear planes probed in electrophoresis, thereby implying the existence of OH − gradients in the interfacial region. This fact could account for the weak OH − signals detected by surface-specific spectroscopies.gas-liquid reactions | surface potential | water surface acidity | interfacial proton transfer A cid-base chemistry at aqueous interfaces lies at the heart of major processes in chemistry and biology. Changes in the degree of dissociation of the acidic/basic residues upon translocation between aqueous and hydrophobic microenvironments orchestrate enzyme catalysis (1), drive proton/electron transport across biomembranes (2, 3), and mediate molecular recognition and self-assembly phenomena (4-6). Despite its importance, the characterization of acid-base chemistry at aqueous interfaces remains fraught with uncertainties (7-11). Basic questions linger about the thickness of interfacial layers (12), how acidity changes through the interfacial region (13), and the mechanistic differences between proton transfer (PT) across interfacial (IF) versus in bulk (B) water (10,14). Because aqueous surfaces are usually charged relative to the bulk liquid (15), the thermodynamic requirement of uniform electrochemical activity throughout (including the interfacial regions) implies that the chemical activity of protons (pH) in IF could be different from that in the B liquid. Reduced hydration of ionic species at the interface could force acids and bases toward their undissociated forms (16).These fundamental issues have been extensively investigated via electrostatic (17) and electrokinetic experiments (11), surface tension studies and analysis (1...

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Section: Quantum-mechanical Calculationsmentioning

confidence: 99%

Brønsted basicity of the air–water interface

Mishra

Enami

Nielsen

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

172

203

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“…VDEs and the first three excitation energies for e − (H 2 O) 4 and e − (H 2 O) 6 clusters embedded in a polarizable continuum model of the solvent in geometries depicted in Fig. 1 6 , respectively, which is close to the experimentally determined VDEs from different photoelectron spectroscopy studies on liquid microjet ranging from 3.3 to 3.6 eV [14][15][16][17]. The optical spectrum of the hydrated electron is constituted by three s → p-like transitions lying around 1.7 eV and a slowly decaying blue tail [41].…”

Section: Embedded Cluster Models For E − Aqmentioning

confidence: 55%

“…Only in the last few years, photoelectron spectroscopy (PES) in aqueous microjets allowed to determine the vertical binding energy of an electron solvated in bulk liquid water, amounting to 3.3-3.6 eV [14][15][16][17]. Calculations showed, that the most strongly bound isomers in large cryogenic clusters bear some resemblance to the ambient bulk hydrated electron, while the more weakly bound cluster isomers do not have an analogue in the liquid [18,19].…”

Section: Introductionmentioning

confidence: 99%

Embedded Cluster Models for Reactivity of the Hydrated Electron

Uhlig

Jungwirth

2013

Zeitschrift Für Physikalische Chemie

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Hydrated Electron / Reactivity / Clusters / Hydronium / Nitrous OxideOur computational study presents embedded cluster models of the hydrated electron focusing on its reactivity with the hydrated proton and the nitrous oxide molecule leading to formation of a hydrogen atom in the former case and a nitrogen molecule plus hydroxyl radical and hydroxide anion in the latter case. We show using ab initio calculations combined with the nudged elastic band method for determining minimum energy paths that carefully chosen cluster models with no more than six water molecules embedded in a polarizable continuum are able to capture the essential features of the reactive processes of the hydrated electron.

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“…Importantly though, a significant fraction of the CTTS-state manifold, with energies fairly near the CTTS lowest state, is populated instantaneously by one-photon absorption. Relaxation of the CTTS states occurs within 100 -500 fs [13,15,12]. The observed spread in time constants is associated with aforementioned structure diversity.…”

Section: Introductionmentioning

confidence: 99%

“…In this case no solute intramolecular effects need to be accounted for. Although resonant excitation is indeed a crucial factor in previous experimental studies of the CTTS dynamics, the resonance condition is rather loosely defined since photon energies vary considerably in different experiments, typically between 5.1 and 6.2 eV [13,14,15,16]. Importantly though, a significant fraction of the CTTS-state manifold, with energies fairly near the CTTS lowest state, is populated instantaneously by one-photon absorption.…”

Section: Introductionmentioning

confidence: 99%