Dipole-quadrupole Theory of Surface Enhanced Raman Scattering

by Polubotko, A. m.

• ISBN13: 9781606925799
• ISBN10: 1606925792
• Format: Paperback
• Copyright: 2009-04-01
• Publisher: Gardners Books

Summary

This book is devoted to explanation of SERS in terms of the strong dipole and especially quadruple light-molecule interactions arising in surface fields strongly varying in space in the region of strongly irregular surface roughness. The influence of the quadruple interaction is a matter of principle, since it provides explanation for the appearance of forbidden bands arising in a great number of experiments on SERS on symmetrical molecules. This essential detail in fact is absent in all other SERS theories, that does not permit to create a closed theory, which explains the majority of experimental facts accompanying SERS by a unitary approach. Moreover as it is demonstrated in the book the huge enhancement in the phenomenon of Single Molecule Detection by the SERS method can be explained exclusively by the strong quadruple light-molecule interaction. The first part of the book is devoted to a brief description of main SERS characteristics and critical analysis of theoretical approaches. Further the theory of electromagnetic field near some model kinds of rough surfaces and some other systems and the theory of the SER cross-section for arbitrary and symmetrical molecules are presented in detail. The obtained expressions helps to establish selection rules for contributions in the SER cross-section and analyse the SER spectra of symmetrical molecules. This analysis corroborates main specific features of the SER spectra of symmetrical molecules and some anomalies, which exist in these spectra for some specific conditions. The existence of electrodynamic forbiddance of the quadruple scattering mechanism for the methane molecule and molecules with cubic symmetry groups is established. The above theory permits to explain not only the huge enhancement in the phenomenon of Single -Molecule Detection but the blinking of the SERS signal too. The first layer effect, arising in the first layer of absorbed molecules also is considered in detail. It appears that the nature of this phenomenon is the electrodynamic enhancement, which is very large just in the first layer. The other phenomena, accompanying SERS are accounted for. It is demonstrated that the theory is in a good agreement with the SERS experiments and explains quite a number of characteristics related to the SERS phenomenon.

Table of Contents

Preface

Introduction

Main Specific Features of the SERS phenomenon

Some of the Existing Theories

Some Properties of the Electromagnetic Field Near a Rough Metal Surface

Expressions for the SER Cross-Sections of Arbitrary and Symmetrical Molecules

Selection Rules For Symmetrical Molecules

Classification of the Contributions by the Degree of Enhancement

Most Enhanced Bands in SERS

(dz-Qmain), (Qmain-dz) and (dz-dz) Contributions and Appearance of Forbidden Bands in the SER Spectra of Symmetrical Molecules

Contributions Caused by One Minor and One Main Moments

Disturbance of the Symmetry of Molecules Upon Adsorption and Two Possible Mechanisms of the Appearance of Forbidden Bands in the SER Spectra

Analysis of the SER Spectra

Analysis of the SER Spectra of Molecules With and Symmetry Groups

Anomalies in the SER Spectra of Benzene Adsorbed on Lithium and Hexafluorobenzene Adsorbed on Silver

Electrodynamic Forbiddance of the Quadrupole Enhancement Mechanism in Molecules with Cubic Symmetry Groups

Discussion of Experimental Results

About the Electrodynamic Forbiddance of the Quadrupole SERS Mechanism in Other Molecules

Anomalies of the SER Spectra of Symmetrical Molecules Adsorbed on Transition Metal Substrates

Possible Reason of the Competition of the Raman Bands (Influence of the Complex Dielectric Constant)

Single Molecule Detection by the SERS Method and Its Relation to the Quadrupole SERS Theory

Charge Transfer Enhancement Mechanism

Explanation of Experimental Phenomena Accompanying SERS

Conclusion

Wave functions of Arbitrary Molecules

The Tables of Irreducible Representations of Some Point Groups

References

Index

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