SURFACE ENHANCED RAMAN SPECTROSCOPY ON ELECTRODES: ENHANCEMENT MECHANISMS AND APPLICATION TO THE STUDIES OF FLAVIN MOLECULES.
Item
-
Title
-
SURFACE ENHANCED RAMAN SPECTROSCOPY ON ELECTRODES: ENHANCEMENT MECHANISMS AND APPLICATION TO THE STUDIES OF FLAVIN MOLECULES.
-
Identifier
-
AAI8708327
-
identifier
-
8708327
-
Creator
-
XU, JIA.
-
Contributor
-
Ronald L. Birke | John R. Lombardi
-
Date
-
1987
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Chemistry, Physical
-
Abstract
-
A comprehensive development of the charge-transfer theory of surface enhanced Raman scattering (SERS) is presented. It was done by incorporating the Herzberg-Teller mixing of zero-order Born-Oppenheimer electronic states by means of vibronic interaction terms in the Hamiltonian. The theory is comprehensive in that both molecule-to-metal and metal-to-molecule transfer is considered. Furthermore, both Frank-Condon and Herzberg-Teller contributions to the intensity are obtained. The former, however, contribute only to the intensity of totally symmetric vibrations, while the latter contribute to nontotally symmetric vibrations as well. The resulting formulas may be interpreted as a type of resonance Raman effect in which intensity for the charge transfer transitions is borrowed from an allowed molecular transition. Based on this theory and the electromagnetic enhancement factors obtained from the small sphere model, the determination of molecular orientation at metal surfaces is discussed and applied for pyridine molecules on a Ag electrode at different potentials.;The surface enhanced Raman scattering (SERS) spectroscopy of protein-free flavin in different redox states was investigated at a silver electrode. Good quality spectra for oxidized flavin with an excitation frequency within the absorption band (488 or 514.5 nm) and out of the absorption band (yellow-red region) are reported. Fluorescence interference from the flavin is nearly completely quenched by the surface interaction. The bonding sites of the flavin on a silver electrode appear to be at N(,5) and O(,4) positions of the isoalloxazine ring based upon the results of N(,3)-H deuterium substitution and from the SERS spectral analysis. Reduced flavin did not exhibit a well defined SERS spectrum, probably because of the break down of the surface complex. The SERS spectrum of the neutral semiquinone radical, as an intermediate of the two single electron reduction steps, was observed in acidic solution with yellow or red excitation. The utility of SERS as a technique for probing the existence of an unstable intermediate species at the electrode surface is demonstrated.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
-
Program
-
Chemistry
