Surface enhanced Raman spectroscopy studies of lumazine, piperidine and 2-mercaptopyridine on a silver electrode.
Item
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Title
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Surface enhanced Raman spectroscopy studies of lumazine, piperidine and 2-mercaptopyridine on a silver electrode.
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Identifier
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AAI3024771
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identifier
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3024771
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Creator
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Chen, Xingxing.
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Contributor
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Advisers: Ronald L. Birke | John R. Lombardi
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Date
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2001
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Analytical
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Abstract
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Surface-enhanced Raman spectroscopy (SERS) at a silver electrode was used to obtain the Raman spectrum of lumazine free of interference from fluorescence. The study was carried out varying the experimental conditions of voltage and pH. Ab initio calculations at the Hartree-Fock/6-31G(d) level were made of the vibrational spectra of lumazine [2,4(3H,8H)-pterdinedione, LUM] and dimethyllumazine [6,7-dimethyl,2,4(3H,8 H)-pterdinedione, DML], and these were compared with the experimental results. Band assignments were made for LUM and DML. In addition, to determining the structure of the molecules on the metal surface as well as to examining the effects of the surface on the observed spectrum, we compared the results with the FTIR spectrum of a known metal complex of LUM. We also analyzed band shifts and the intensity ratio of in-plane and out-of-plane modes as a function of potential. This analysis indicates that the LUM molecules are tilted at an angle of ca. 45 degree (0.0 to -0.3 V) to the surface interacting as dimers with silver (Ag) sites through the lone pairs on the 1N or 5N atoms of the LUM ring. The tilt angle moves to ca. 50 degree as the potential is made more negative (-0.6 to -0.7 V).;The enhancement factor of the surfaced enhanced Raman scattering spectra of a molecule on metal electrode is well known to be potential and incident wavelength dependent. A quantitative potential-dependence study of SERS of piperidine and 2-mercaptopyridine on the Ag electrode is presented. The result shows that the surface concentration of piperidine adsorbed on the Ag electrode is a constant over the potential range from 0.0V to -0.9V vs. SCE. Two structural isomers exist on the surface. The concentration of each species is a function of applied potential. 2-mercaptopyridine is adsorbed on Ag surface via Ag-S bond. The orientation of the molecule changes with the applied potential. Experimentally, the SERS of 2-mercaptopyridine is much stronger than the SERS of 2-piperidine, which implies that the strength of chemical bond between adsorbate and metal is related to the chemical enhancement factor.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
