Vibrational spectroscopy of geochemical interfaces

Piontek, Stefan; Borguet, Eric

doi:10.1016/j.surfrep.2023.100606

Cited by 7 publications

(2 citation statements)

References 209 publications

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“…At the SiO 2 surface, the organization of acetonitrile has been found to resemble a supported bilayer even in the presence of H 2 O, ,, due to the hydrophobic interactions between the methyl groups. ,, The influence of surface charge on the organization of H 2 O–acetonitrile mixtures at silica surfaces has been investigated via the vSFG response of the CH stretching modes of acetonitrile . Rehl et al found that moving the solution from neutral to basic conditions reduced the number density of interfacial acetonitrile molecules disrupting an acetonitrile-rich layer near the interface, which was attributed to the magnitude of the external electric field generated from the deprotonation of surface SiOH sites at higher pH .…”

Section: Introductionmentioning

confidence: 99%

“…In this work, we hypothesize that the organization and the local electric field experienced by the solvent are influenced by the oxide surface charge, which is controlled by the acidic and basic properties of the surface as well as the surface site density . We tested this hypothesis by investigating H 2 O–acetonitrile mixtures at the α-Al 2 O 3 (0001) and SiO 2 interfaces as a function of pH with vSFG in the nitrile stretching region of acetonitrile.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Charged Site Density on Local Electric Fields and Polar Solvent Organization at Oxide Interfaces

Dadashi,

Parshotam,

Mandal

et al. 2024

J. Phys. Chem. C

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The characteristics of oxide surfaces such as their hydroxyl density, the associated acid−base chemistry, and the resulting surface charge play a crucial role in modulating the solvent organization and electrostatics at interfaces found in chemical and environmental processes. Here, the nitrile mode of acetonitrile, a neutral Stark-active molecule, is used to probe the local electric fields and solvent organization that result from surface charge at the α-Al 2 O 3 (0001)/aqueous and SiO 2 /aqueous interfaces using vibrational sum frequency generation (vSFG). The vSFG response in the C�N stretch region for H 2 O−acetonitrile mixtures displays an asymmetric line shape and unique pH-dependent behavior, which we attributed to interference with the H 2 O combination (bend + libration). Stark spectroscopy results at both interfaces reveal that the density of surface hydroxyl groups influences the magnitude of the local electric field experienced by acetonitrile. While the nitrile group of acetonitrile probes single-point charges at the SiO 2 surface at pH 6−11, the local electric field sampled by the nitrile group at the Al 2 O 3 interface is impacted by multiple charged hydroxyl sites at elevated pH. These findings highlight the influence of inhomogeneous surface-charging behavior on interfacial solvent structure and local electric fields.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Influence of Charged Site Density on Local Electric Fields and Polar Solvent Organization at Oxide Interfaces

Dadashi,

Parshotam,

Mandal

et al. 2024

J. Phys. Chem. C

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Sum frequency generation (SFG) spectroscopy at surfaces and interfaces: Adsorbate structure and molecular bond orientation

Li,

Rupprechter

2024

Surface Science Reports

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Detecting Centrosymmetric Molecular Ions at an Interface with Vibrational Sum Frequency Generation Spectroscopy

Mandal,

Dadashi,

Kumagai

et al. 2024

J. Phys. Chem. C

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Under the electric dipole approximation, second-order nonlinear optical phenomena, such as vibrational sum frequency generation (vSFG) and second harmonic generation (SHG), are forbidden in centrosymmetric environments, making them surfacespecific processes where the centrosymmetry is inherently broken and suitable for studying interfacial chemistry. Although the underlying theory of vSFG/SHG pertaining to centrosymmetry has been extensively studied, fundamental questions remain to be addressed. For example, what leads to the breaking of centrosymmetry in a centrosymmetric molecule at interfaces? Is the interface capable of perturbing the environment of a centrosymmetric molecule, rendering it vSFG active? At what point does the centrosymmetric molecule lose its centrosymmetry to become vSFG active? In this work, we address such basic questions by studying the vSFG response from the azido stretch of N 3 − , a centrosymmetric molecule, at the α-Al 2 O 3 (0001)/H 2 O interface. We observed the azido asymmetric stretch vSFG response at the aqueous alumina interface. There are several possible mechanisms that render this centrosymmetric molecule vSFG active, including dipole and quadrupole mechanisms. Therefore, we analyzed the possible vSFG mechanisms of the azide signal via electronic structure calculations and AIMD simulations. We show that a uniaxial electric field acting on centrosymmetric azide, whose modes are either IR or Raman active but never both, can make modes simultaneously IR and Raman active, but this turns out not to be enough to explain the sum frequency activity that we observe. The electronic structure calculations revealed that azide has sufficiently large quadrupolar susceptibility, which provides the dominant contribution in the azide vSFG response.

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Vibrational spectroscopy of geochemical interfaces

Cited by 7 publications

References 209 publications

Influence of Charged Site Density on Local Electric Fields and Polar Solvent Organization at Oxide Interfaces

Influence of Charged Site Density on Local Electric Fields and Polar Solvent Organization at Oxide Interfaces

Sum frequency generation (SFG) spectroscopy at surfaces and interfaces: Adsorbate structure and molecular bond orientation

Detecting Centrosymmetric Molecular Ions at an Interface with Vibrational Sum Frequency Generation Spectroscopy

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