Vibrational Spectroscopy of Adsorbates

194 Pages·1980·4.715 MB·English

by  Roy F. Willis (auth.), Dr. Roy F. Willis (eds.)

15
Springer Series in Chemical Physics
Edited by R. Gomer
Springer Series in Chemical Physics
Editors: V. 1. Goldanskii R. Gomer F. P. Schafer 1. P. Toennies
Volume 1 Atomic Spectra and Radiative Transitions By I. I. Sobelman
Volume 2 Surface Crystallography by LEED Theory, Computation
and Structural Results By M. A. Van Hove, S. Y. Tong
Volume 3 Advances in Laser Chemistry Editor: A. H. Zewail
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Editors: C. V. Shank, E. P. Ippen, S. L. Shapiro
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By W Demtr6der
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Volume 7 Excitation of Atoms and Broadening of Spectral Lines
By I. I. Sobelman, L. A. Vainshtein, E. A. Yukov
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Chemistry and Biology
By Yu. N. Molin, K M. Salikhov, K I. Zamaraev
Volume 9 Secondary Ion Mass Spectrometry SIMS II
Editors: A. Benninghoven, C. A. Evans, Jr.,
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Volume 10 Lasers and Chemical Change
By A. Ben-Shaul, Y. Haas, K L. Kompa, R. D. Levine
Volume 11 Liquid Crystals of One-and Two-Dimensional Order
Editors: W Helfrich, G. Heppke
Volume 12 Gasdynamic Lasers By S. A. Losev
Volume 13 Atomic Many-Body Theory By I. Lindgren, 1. Morrison
Volume 14 Picosecond Phenomena II
Editors: R. Hochstrasser, W. Kaiser, C. V. Shank
Volume 15 Vibrational Spectroscopy of Adsorbates Editor: R. F. Willis
Vibrational Spectroscopy
of Adsorbates
Editor: R F. Willis
With Contributions by
B. K. Agrawal G. Allan 1. A. Creighton
B. Djafari-Rouhani L. Dobrzynski B. Feuerbacher
P. Hollins D. A. King D. M. Newns
1. Pritchard N. Sheppard D. G. Walmsley
R. F. Willis C. 1. Wright
With 97 Figures
Springer-Verlag Berlin Heidelberg New York 1980
Dr. Roy F. Willis
Cavendish Laboratory, University of Cambridge,
Cambridge CB3 OHE, England
Series Editors Professor Dr. Fritz Peter Schafer
Professor Vitalii I. Goldanskii Max-Planck-Institut fUr
Biophysikalische Chemie
Institute of Chemical Physics D-3400 Gottingen-Nikolausberg
Academy of Sciences Fed. Rep. of Germany
Vorobyevskoye Chaussee 2-b
Moscow V-334, USSR
Professor Robert Gomer Professor Dr. 1. Peter Toennies
The James Franck Institute Max-Planck-Institut fUr Stromungsforschung
The University of Chicago Bottingerstrafie 6-8
5640 Ellis Avenue D-3400 Gottingen
Chicago, IL 60637, USA Fed. Rep. of Germany
ISBN-13: 978-3-642-88646-1 e-ISBN-13: 978-3-642-88644-7
DOl: 10.1007/978-3-642-88644-7
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Preface
Over the past few years, there has been a growing awareness of the vibratio
nal properties of solid surfaces and adsorbates due to a steady growth in
the number of experimental techniques which have evolved with sufficient
resolution and surface sensitivity. An understanding of the surface vibratio
nal modes is of fundamental importance in many areas of the physics and
chemistry of surfaces, most notably in the field of heterogeneous catalysis
on metals and alloys.
The present volume derives from a one day meeting of invited lectures,
held under the auspices of the Thin Films and Surfaces Section of the Insti
tute of Physics in the Cavendish Laboratory, University of Cambridge,
13 December 1979. The object was to bring together specialists from various
diverse fields who would examine the wide variety of methods currently avail
able for studying surface adsorbate vibrations. Since these methods cover
several scientific disciplines, it was subsequently felt that it would be
useful to provide a permanent record of the talks as a source lor future
reference by workers in what is rapidly becoming an expanding field of',inter
est in an increasing number of laboratories. The contributions, however, are
not in any way meant to constitute exhaustive reviews. Rather the effort has
been directed more towards providing an introduction to the already extensive
literature which exists in each subject field, stressing more the fundamental
principles underscoring the various techniques, current problem areas, future
directions, etc., so as to reflect the seminar nature of the original proc
eedings.
Following a brief introduction (Chapter 1), electron-energy-loss spectro
scopy, which has provided enormous impetus to this field, is introduced in
Chapters 2 and 3. The importance of dipole selection rules for scattering in
the specularly reflected electron beam direction is emphasized in Chapter 2,
with angle and impact-energy dependent studies discussed in Chapter 3. The
collective nature of adsorbate-induced surface (optical) phonon modes is de
scribed in Chapter 4. The methods of inelastic electron tunnelling spectro
scopy of adsorbate vibrations (Chapter 5), inelastic molecular beam scatter
ing (Chapter 6), and inelastic neutron scattering (Chapter 7) studies of
surfaces provide additional complimentary information. The optical techni
ques of infrared reflectance absorption spectroscopy and surface enhanced
Raman spectroscopy are described in Chapters 8 and 9, respectively. The
relationship between the vibrational modes of adsorbate species in metal
cluster compounds and complexes is compared with similar vibrations of ad
sorbates on metal surfaces (Chapter 10).Finally, a specific case illustrating
the importance of vibrational coupling between adsorbates viz. carbon
monoxide adsorbed on Pt(100) and Pt(lll) surfaces is described (Chapter 11).
The number of adsorbate systems described has been purposely limited,
examples being drawn from an extensive literature only in so far as to
illustrate the principles behind each method. In this way, it is hoped that
this collection of articles will serve its main purpose of introducing
readers to current methods of research into the vibrational properties of
adsorbates.
Cambridge, July 1980 Roy F. Willis
VI
Contents
1. Introduction
By Roy F. Willis ................................................ .
1.1 Vibrational Spectroscopy in Relation to Surface Science .... .
1.2 Techniques in Surface Vibrational Spectroscopy 2
1.3 Vibrational Coupling and Surface Phonon Modes 4
References 5
2. Theory of Dipole Electron Scattering from Adsorbates
By D.M. Newns (With 11 Figures) .................................. 7
References 22
3. Angle and Energy Dependent Electron Impact Vibrational Excitation
of Adsorbates
By Roy F. Will is (With 23 Figures) ............................... 23
3.1 Background .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2 Inelastic Electron Scattering from Oriented Molecules 24
3.3 Surface Dipole Scattering . ..... .... ...... ...... ......... .... 28
3.3.1 Modes Perpendicular to, the Surface ................... 30
3.3.2 Surface Trapping in Bound State Surface Resonances 32
3.3.3 Modes Parallel to the Surface ........................ 34
3.4 Dipole Theory of One-Phonon Excitation 35
3.5 Multiple Scattering Theory of One-Phonon Excitation ........ . 40
3.6 Hydrogen Modes on W(100) ................................... . 45
3.6.1 Ang 1e Dependence .................................... . 45
3.6.2 Phonon Sidebands Linewidth 48
3.6.3 Impact Energy Dependence .. ... ..... ....... ..... .... ... 49
3.7 Concluding Remarks 51
References 52
4. Adsorbate Induced Optical Phonons
By L. Dobrzynski, G. Allan, B. Djafari-Rouhani, and B.K. Agrawal
(With 4 Figures) ................................................. 55
4.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.2 A Short Review .............................................. 55
4.3 Some Physical Effects ....................................... 56
4.4 Hydrogen on (001) Surface of Tungsten ....................... 59
4.5 Oxygen on the (Ill) Surface of Nickel 62
4.6 Conclusion 64
References 65
5. Inelastic Electron Tunnelling Spectroscopy
By D.G. Walmsley (With 19 Figures) ............................... 67
5.1 Background . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . 67
5.2 lETS . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 69
5.2.1 Principle of lETS .................................... 69
5.2.2 Nature of Interaction ................................ 71
5.2.3 Linewidths 72
5.2.4 Sensitivity and Surface Coverage 75
5.3 Oxides 77
5.3.1 Clean Aluminium Oxide ............................... . 77
5.3.2 Formic Acid on Aluminium Oxide ...................... . 78
5.3.3 Clean Magnesium Oxide ................................ 80
5.3.4 Formic Acid on Magnesium Oxide . ............ ....... ... 82
5.4 Comparison .................................................. 83
5.4.1 Comparison with Electron Energy Loss Spectroscopy(EELS) 83
5.4.2 Comparison with Surface Infrared and Raman Spectro-
scopies ........................................ , ..... 85
5.5 Adsorbate Orientation ....................................... 85
5.6 Conclusion .................................................. 88
References 88
6. Inelastic Molecular Beam Scattering from Surfaces
By B. Feuerbacher (With 15 Figures) .............................. 91
6.1 Bac kground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.2 Atom Scattering from Surfaces 92
6.3 Experimental Considerations '95
6.3.1 Beam Sources 96
VIII
6.3.2 Detectors 97
6.3.3 Systems 98
6.4 Data Interpretation ........................................ . 99
6.4.1 Selection of Scattering Conditions .................. . 99
6.4.2 Selection Rules ..................................... . 100
6.4.3 Scattering Kinematics ................................ 101
6.5 Experimental Results .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.5.1 Inelastic Studies Without Energy Resolution .......... 103
6.5.2 Velocity Resolved Studies ............................ 104
6.5.3 Dispersion Relations 106
6.6 Conclusions and Outlook 109
References 110
7. Neutron Scattering Studies
By C.J. Wright (With 6 Figures) .................................. 111
7.1 Theoretical Background ...................................... 112
Experimental Considerations ................................. 115
7.2 Appl ications ................................................ 117
7.2.1 Sulphide Catalysts ................................... 118
7.2.2 Butane Adsorption Upon Graphite ....................... 120
7.2.3 C6H6 Adsorbed on Raney-Nickel ........................ 121
7.2.4 Collective Excitations ............................... 121
7.3 Future Considerations 122
References 123
8. Reflection Absorption Infrared Spectroscopy: Application to Carbon
Monoxide on Copper
By P. Hollins and J. Pritchard (With 10 Figures) ..... '" ......... 125
8.1 Background .................................................. 125
8.2 Physical Factors in Infrared Reflection at Metal Surfaces 126
8.3 Experimental Aspects ........................................ 129
8.4 Some Applications of RAIRS .................................. 130
8.5 Spectra of CO on Copper ..................................... 130
8.6 Coupling Effects in Vibrational Spectra 132
8.7 Modified Dipole Coupling Theories .......................... . 135
8.8 Di po 1e Cou p1 i ng in Is 1a nd s ................................. . 138
References 141
IX
9. Raman Spectroscopy of Adsorbates at Metal Surfaces
By J.A. Creighton (With 12 Figures) ............................. 145
9.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
9.2 Experimental Features 146
9.3 Enhanced Raman Spectra of Adsorbates on Silver Surfaces 148
9.4 Enhanced Raman Spectra of Adsorbates at Metal Other Than
Silver ...................................................... 153
9.5 The SERS Selection Rule 154
9.6 Some Observations on the Mechanism of the Surface Raman
Enhancement ....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
References 162
10. Vibrations of Monatomic and Diatomic Ligands in Metal Clusters and
Complexes - Analogies with Vibrations of Adsorbed Species on Metals
By N. Sheppard .................................................. . 165
10.1 Background ................................................ . 165
10.2 Hydrogen as Adsorbed Species or as a Ligand on Metals 166
10.3 Carbon Monoxide as Adsorbed Species and Ligands ........... . 169
10.4 Nitrogen as Adsorbed Species and as Ligands ............... . 170
10.5 Oxygen as Adsorbed Species and as Ligands ................. . 172
10.6 Nitric Oxide, NO, as Adsorbed Species and as Ligands 173
10.7 General Conclusions 174
References 176
11. Coupling Induced Vibrational Frequency Shifts and Island Size
Determination: CO on Pt{OOl} and Pt{lll}
By D.A. King (With 3 Figures) ..................................... 179
11.1 Background ................................................. 179
11.2 CO on Pt{OOl}: Island Growth ............................... 179
11.3 CO on Pt{lll}: "Gaseous" and Island Species 182
11.4 Conclusion 183
References 183
x