The application of SERS to the determination of relative adsorption strengths of nitrogen heterocycles on silver electrodes

Persistent Link:
http://hdl.handle.net/10150/290662
Title:
The application of SERS to the determination of relative adsorption strengths of nitrogen heterocycles on silver electrodes
Author:
Carter, David Allen, 1958-
Issue Date:
1996
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Research was undertaken to explore the application of surface enhanced Raman scattering (SERS) to the understanding of electrosorption phenomena. In particular, the relative strength of interactions between the functional groups of imidazole (N₁, N₂ and the π orbitals) on Ag electrodes was examined. This information is useful in understanding how the presence of these functional groups contributes to the relative adsorption strength of nitrogen heterocycles. A Raman spectrometer equipped with a charge-coupled device (CCD) detector was required to obtain reproducible SERS spectra in this research. It was also necessary to obtain accurate Raman shifts so that small (ca. 1-2 cm⁻¹ vibrational frequency changes between adsorbed and solution species could be detected. Therefore, significant effort was expended to develop calibration and spectral acquisition procedures which would provide acceptable accuracy and efficiency. Instrumental factors affecting Raman spectral calibration were studied. Available Raman shift calibration standards are reviewed and improved Raman shift data for these standards are reported. Several methods for the conversion of CCD position (pixel number) data to wavelength and Raman shifts are appraised using both experimental and simulated Raman data. SERS spectra for imidazole, 1-methylimidazole, and 2-methylimidazole support the conclusion that these molecules are adsorbed to the Ag electrode through the "pyridine nitrogen" (N₃). This evidence includes vibrational frequency shifts and orientations of these molecules deduced from the consideration of SERS surface selection rules. These data also suggest that the π orbital of the C=N bond interacts with the electrode at potentials near -0.25 V (versus SCE reference electrode) producing a tilt of the ring relative to the surface at these potentials. At potentials near the potential of zero charge (ca. -0.80 V), this interaction is minimized and these molecules assume a more vertical position. At the most negative potentials examined, the methylimidazoles interact with the surface predominantly through the methyl group. Preliminary work on the application of SERS to obtain surface coverage information was performed. An increase in SERS intensity with increasing solution concentration suggests adsorption isotherm-like behavior.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Chemistry, Analytical.; Chemistry, Physical.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Pemberton, Jeanne E.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleThe application of SERS to the determination of relative adsorption strengths of nitrogen heterocycles on silver electrodesen_US
dc.creatorCarter, David Allen, 1958-en_US
dc.contributor.authorCarter, David Allen, 1958-en_US
dc.date.issued1996en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractResearch was undertaken to explore the application of surface enhanced Raman scattering (SERS) to the understanding of electrosorption phenomena. In particular, the relative strength of interactions between the functional groups of imidazole (N₁, N₂ and the π orbitals) on Ag electrodes was examined. This information is useful in understanding how the presence of these functional groups contributes to the relative adsorption strength of nitrogen heterocycles. A Raman spectrometer equipped with a charge-coupled device (CCD) detector was required to obtain reproducible SERS spectra in this research. It was also necessary to obtain accurate Raman shifts so that small (ca. 1-2 cm⁻¹ vibrational frequency changes between adsorbed and solution species could be detected. Therefore, significant effort was expended to develop calibration and spectral acquisition procedures which would provide acceptable accuracy and efficiency. Instrumental factors affecting Raman spectral calibration were studied. Available Raman shift calibration standards are reviewed and improved Raman shift data for these standards are reported. Several methods for the conversion of CCD position (pixel number) data to wavelength and Raman shifts are appraised using both experimental and simulated Raman data. SERS spectra for imidazole, 1-methylimidazole, and 2-methylimidazole support the conclusion that these molecules are adsorbed to the Ag electrode through the "pyridine nitrogen" (N₃). This evidence includes vibrational frequency shifts and orientations of these molecules deduced from the consideration of SERS surface selection rules. These data also suggest that the π orbital of the C=N bond interacts with the electrode at potentials near -0.25 V (versus SCE reference electrode) producing a tilt of the ring relative to the surface at these potentials. At potentials near the potential of zero charge (ca. -0.80 V), this interaction is minimized and these molecules assume a more vertical position. At the most negative potentials examined, the methylimidazoles interact with the surface predominantly through the methyl group. Preliminary work on the application of SERS to obtain surface coverage information was performed. An increase in SERS intensity with increasing solution concentration suggests adsorption isotherm-like behavior.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectChemistry, Analytical.en_US
dc.subjectChemistry, Physical.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorPemberton, Jeanne E.en_US
dc.identifier.proquest9720599en_US
dc.identifier.bibrecord.b34528350en_US
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