Variation of the transition dipole moment across the OH stretching band of water

Loparo, Joseph J.; Roberts, Sean T.; Nicodemus, Rebecca A.; Tokmakoff, Andrei

doi:10.1016/j.chemphys.2007.06.056

Cited by 70 publications

(67 citation statements)

References 44 publications

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“…5A shows the calculated 2D IR spectral components as a function of 2 , emphasizing the spectral region probed in our experiments. The component representing HOD/D 2 O appears similar to that which has been calculated from classical simulation models (32,35,37). The spectra of HOD molecules undergoing PT are quite broad, with positive intensity peaked at 3,300 cm Ϫ1 but covering the majority of the OH frequency region.…”

Section: Modeling Based On Empirical Valence Bond MD Simulationssupporting

confidence: 51%

Observation of a Zundel-like transition state during proton transfer in aqueous hydroxide solutions

Roberts

Petersen

Ramasesha

et al. 2009

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

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113

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It is generally accepted that the anomalous diffusion of the aqueous hydroxide ion results from its ability to accept a proton from a neighboring water molecule; yet, many questions exist concerning the mechanism for this process. What is the solvation structure of the hydroxide ion? In what way do water hydrogen bond dynamics influence the transfer of a proton to the ion? We present the results of femtosecond pump-probe and 2D infrared experiments that probe the O-H stretching vibration of a solution of dilute HOD dissolved in NaOD/D2O. Upon the addition of NaOD, measured pump-probe transients and 2D IR spectra show a new feature that decays with a 110-fs time scale. The calculation of 2D IR spectra from an empirical valence bond molecular dynamics simulation of a single NaOH molecule in a bath of H2O indicates that this fast feature is due to an overtone transition of Zundel-like H3O 2 ؊ states, wherein a proton is significantly shared between a water molecule and the hydroxide ion. Given the frequency of vibration of shared protons, the observations indicate the shared proton state persists for 2-3 vibrational periods before the proton localizes on a hydroxide. Calculations based on the EVB-MD model argue that the collective electric field in the proton transfer direction is the appropriate coordinate to describe the creation and relaxation of these Zundel-like transition states.Grotthuss mechanism ͉ 2D infrared spectroscopy P roton transfer in water is the process at the heart of biological redox chemistry and energy conversion processes such as photosynthesis and cellular respiration (1). Although its extraordinary speed and efficiency has generally been attributed to the rearrangement of O-H bonds that effectively move the charge rather than a specific proton, the water structure around the charge defect and the mechanism of translocation remain challenging to study experimentally. Researchers commonly discuss the solvated excess proton in terms of 2 limiting structures, the Eigen cation (2), a triply solvated hydronium ion (H 3 O ϩ ⅐3H 2 O), and the Zundel ion (3), a proton equally shared between 2 water molecules (H 5 O 2 ϩ or H 2 O⅐H⅐OH 2 ϩ ). However, the difference in energy between these 2 configurations is small, on the order of the energy of a hydrogen bond (2-3 kcal/mol) (4), which allows these structures to interconvert on femtosecond to picosecond time scales (5, 6). Thus, to meaningfully address the structure of the excess proton, one must also consider its dynamics. Similar questions related to this view of aqueous proton transfer (PT) exist for the hydroxide ion, whereby proton transfer occurs from water to OH Ϫ . What are the ion's limiting structures, and in what manner do changes in the water structure influence the ion's structural diffusion?Initial proposals for transport of the hydroxide ion described the process as the mirror image of that observed in acids (7) and postulated the existence of a stable H 3 O 2 Ϫ state (8). Ab initio simulations (9-11) suggest a different scenario in whi...

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Section: Modeling Based On Empirical Valence Bond MD Simulationssupporting

confidence: 51%

Observation of a Zundel-like transition state during proton transfer in aqueous hydroxide solutions

Roberts

Petersen

Ramasesha

et al. 2009

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

Self Cite

113

150

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“…15 From the simulations, we extract instantaneous frequencies ω OH (t) and the projection of the OH bond orientation onto the i = x, y and z coordinates. 33 The trajectories are used to calculate rephasing (−) and non-rephasing (+) third order response functions 34,35 according to the semiclassical approximation. obtain 2D IR spectra, and used to calculate 2D anisotropy surfaces.…”

Section: Iib Simulations and Modelingmentioning

confidence: 99%

Ultrafast 2D IR anisotropy of water reveals reorientation during hydrogen-bond switching

Ramasesha

Roberts

Nicodemus

et al. 2011

The Journal of Chemical Physics

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Rearrangements of the hydrogen bond network of liquid water are believed to involve rapid and concerted hydrogen bond switching events, during which a hydrogen bond donor molecule undergoes large angle molecular reorientation as it exchanges hydrogen-bonding partners. To test this picture of hydrogen bond dynamics, we have performed ultrafast 2D IR spectral anisotropy measurements on the OH stretching vibration of HOD in D 2 O to directly track the reorientation of water molecules as they change hydrogen bonding environments. Interpretation of the experimental data is assisted by modeling drawn from molecular dynamics simulations, and we quantify the degree of molecular rotation on changing local hydrogen bonding environment using restricted rotation models. From the inertial 2D anisotropy decay, we find that water molecules initiating from a strained configuration and relaxing to a stable configuration are characterized by a distribution of angles, with an average reorientation half-angle of 10°, implying an average reorientation for a full switch of ≥20°. These results provide evidence that water hydrogen bond network connectivity switches through concerted motions involving large angle molecular reorientation.2

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“…Dies stellt eine Alternative zur direkten Beobachtung der relativen Positionen von Wassermolekülen dar.Die zentrale Frequenz und Signalform der O-H-Streckschwingung (in H 2 O) ist bekannt dafür, empfindlich von der Stärke und der Topologie der Wasserstoffbrücken abhängig zu sein. [23] Eine O-H···O-Brücke,deren Stärke vom intermolekularen H···O-Abstand und dem Winkel der Orientierung des Akzeptors [24] [25][26][27] Diese Te chniken sind jedoch nicht oberflächenspezifisch. Um Informationen über die Struktur und das H-Brückennetzwerk von Wassermolekülen an Grenzflächen zu erhalten, muss die Schwingungsfrequenz einzig der Moleküle an der Grenzflä-che gemessen werden.…”

Section: Methode:grenzflächenspezifische Sfg-spektroskopieunclassified

Untersuchung der Struktur und Dynamik von Wasser an der Wasser‐Luft‐Grenzfläche mittels oberflächenspezifischer Schwingungsspektroskopie

2015

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Die Grenzfläche von Wasser zu Luft bietet eine Plattform für viele wichtige biologische, chemische und physikalische Prozesse. Die Wasser‐Luft‐Grenzfläche ist die verbreitetste und einfachste Grenzfläche und dient als Modellsystem für Wasser an hydrophoben Oberflächen. Die Aufklärung der mikroskopischen (<1 nm) Struktur und Dynamik von Wasser an der Wasser‐Luft‐Grenzfläche ist zum Verständnis der an der Wasseroberfläche auftretenden Prozesse unerlässlich. Das Netzwerk sehr starker intermolekularer Wechselwirkungen, der Wasserstoffbrücken (H‐Brücken), ist an der Wassergrenzfläche unterbrochen. Ebenso ist dort die Dichte von Wasser verringert. Eine zentrale Frage bezüglich Wasser an Grenzflächen ist, inwieweit Struktur und Dynamik der Wassermoleküle von Unterbrechungen des H‐Brückennetzwerks beeinflusst werden und sich dadurch von Wasser im Volumen unterscheiden. In diesem Aufsatz werden jüngste Fortschritte in der Untersuchung von Wasser an der Wasser‐Luft‐Grenzfläche mittels Laser‐basierter oberflächenspezifischer Schwingungsspektroskopie diskutiert.

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Variation of the transition dipole moment across the OH stretching band of water

Cited by 70 publications

References 44 publications

Observation of a Zundel-like transition state during proton transfer in aqueous hydroxide solutions

Observation of a Zundel-like transition state during proton transfer in aqueous hydroxide solutions

Ultrafast 2D IR anisotropy of water reveals reorientation during hydrogen-bond switching

Untersuchung der Struktur und Dynamik von Wasser an der Wasser‐Luft‐Grenzfläche mittels oberflächenspezifischer Schwingungsspektroskopie

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