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Surface Vibrational and Electron Spectroscopy - Experiments and first-principle calculations

Andersson, Martin LU (2004)
Abstract (Swedish)
Popular Abstract in Swedish

75% av alla kemiska reaktioner sker på en yta av något slag. En av anledningarna till detta är att många ytor har en katalytisk effekt. Inom kemins värld är en katalysator något som påskyndar en kemisk reaktion utan att själv förbrukas, och ett tydligt exempel på en katalytiskt aktiv yta är en bilkatalysator, vilken i princip består av en varm metallyta. På denna yta omvandlas gaser från motorförbränningen som är giftiga och förstör ozonlagret till ofarliga gaser som sen släpps ut från avgasröret. Vår forskning syftar till att öka förståelsen för den grundläggande växelverkan mellan små organiska molekyler och metallytor. Egenskaper såsom hur en molekyl sitter på metallytan, hur starkt den... (More)
Popular Abstract in Swedish

75% av alla kemiska reaktioner sker på en yta av något slag. En av anledningarna till detta är att många ytor har en katalytisk effekt. Inom kemins värld är en katalysator något som påskyndar en kemisk reaktion utan att själv förbrukas, och ett tydligt exempel på en katalytiskt aktiv yta är en bilkatalysator, vilken i princip består av en varm metallyta. På denna yta omvandlas gaser från motorförbränningen som är giftiga och förstör ozonlagret till ofarliga gaser som sen släpps ut från avgasröret. Vår forskning syftar till att öka förståelsen för den grundläggande växelverkan mellan små organiska molekyler och metallytor. Egenskaper såsom hur en molekyl sitter på metallytan, hur starkt den binder, hur den lutar, e.t.c. styr i sin tur vilka kemiska reaktioner som kan ske på ytan. Genom att kombinera experiment och modellberäkningar kan vi undersöka och dra slutsater om dessa egenskaper och därmed öka förståelsen för bl.a. heterogen katalys. (Less)
Abstract
This work deals with interpretation of experimental surface spectroscopic data with the aid of first-principle calculations. Surface infrared reflection-absorption spectra as well as spectra from the electron spectroscopic methods photoemission and X-ray absorption are considered. In all cases the surface is modeled by a metal cluster with the same (frozen) geometry as part of the surface.



The work on surface vibrational spectra has aimed at including anharmonic effects using first-principles calculations. Anharmonicity influences surface adsorbate vibrations in two ways. First, the frequencies are lowered as compared to the harmonic frequencies. Second, anharmonic resonances mix C-H stretch fundamentals and binary C-H... (More)
This work deals with interpretation of experimental surface spectroscopic data with the aid of first-principle calculations. Surface infrared reflection-absorption spectra as well as spectra from the electron spectroscopic methods photoemission and X-ray absorption are considered. In all cases the surface is modeled by a metal cluster with the same (frozen) geometry as part of the surface.



The work on surface vibrational spectra has aimed at including anharmonic effects using first-principles calculations. Anharmonicity influences surface adsorbate vibrations in two ways. First, the frequencies are lowered as compared to the harmonic frequencies. Second, anharmonic resonances mix C-H stretch fundamentals and binary C-H deformation overtones and combinations and therefore redistribute the harmonic intensity only found in the C-H stretch fundamental. We show that by using a sophisticated model for anharmonicity based on density-functional electronic structure calculations and 2nd order perturbation theory both these effects can be included without scaling the harmonic frequencies. In order to save computational time anharmonic effects are calculated for a corresponding free molecule and excellent agreement between experiments and calculations is demonstrated for a few adsorbates adsorbed on Cu(100). Frequencies, relative intensities and the number of observed modes are all reproduced.



Photoemission and x-ray absorption data have been modeled using electronic structure calculations for the density-functional method B3LYP on metal clusters including only a single metal atom. For the system studied this simple model reproduces virtually all experimental results, such as binding energy shifts, valence photoemission spectra and x-ray absorption spectra and thus allows for easy and detailed spectral interpretation. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Tobin, Roger G., Dep. of Physics and Astronomy, Tufts University, USA
organization
publishing date
type
Thesis
publication status
published
subject
keywords
gränsskikt, anharmonicity, Ytkemi, Surface and boundary layery chemistry, adsorbates, metal surface, density functional theory, first-principle calculations, electron spectroscopy, reflection-absorption infrared spectroscopy, vibrational spectroscpy
pages
224 pages
publisher
Martin Andersson, Östervång 30, 247 32 Södra Sandby, Sweden,
defense location
Lund University, Chemical Center, Lecture hall A
defense date
2004-01-30 13:00
ISBN
91-7422-041-1
language
English
LU publication?
yes
id
d254e622-cd4b-41e3-ab0e-36a9bc2ea64c (old id 466599)
date added to LUP
2007-09-25 20:00:55
date last changed
2016-09-19 08:45:03
@misc{d254e622-cd4b-41e3-ab0e-36a9bc2ea64c,
  abstract     = {This work deals with interpretation of experimental surface spectroscopic data with the aid of first-principle calculations. Surface infrared reflection-absorption spectra as well as spectra from the electron spectroscopic methods photoemission and X-ray absorption are considered. In all cases the surface is modeled by a metal cluster with the same (frozen) geometry as part of the surface.<br/><br>
<br/><br>
The work on surface vibrational spectra has aimed at including anharmonic effects using first-principles calculations. Anharmonicity influences surface adsorbate vibrations in two ways. First, the frequencies are lowered as compared to the harmonic frequencies. Second, anharmonic resonances mix C-H stretch fundamentals and binary C-H deformation overtones and combinations and therefore redistribute the harmonic intensity only found in the C-H stretch fundamental. We show that by using a sophisticated model for anharmonicity based on density-functional electronic structure calculations and 2nd order perturbation theory both these effects can be included without scaling the harmonic frequencies. In order to save computational time anharmonic effects are calculated for a corresponding free molecule and excellent agreement between experiments and calculations is demonstrated for a few adsorbates adsorbed on Cu(100). Frequencies, relative intensities and the number of observed modes are all reproduced.<br/><br>
<br/><br>
Photoemission and x-ray absorption data have been modeled using electronic structure calculations for the density-functional method B3LYP on metal clusters including only a single metal atom. For the system studied this simple model reproduces virtually all experimental results, such as binding energy shifts, valence photoemission spectra and x-ray absorption spectra and thus allows for easy and detailed spectral interpretation.},
  author       = {Andersson, Martin},
  isbn         = {91-7422-041-1},
  keyword      = {gränsskikt,anharmonicity,Ytkemi,Surface and boundary layery chemistry,adsorbates,metal surface,density functional theory,first-principle calculations,electron spectroscopy,reflection-absorption infrared spectroscopy,vibrational spectroscpy},
  language     = {eng},
  pages        = {224},
  publisher    = {ARRAY(0x59e2940)},
  title        = {Surface Vibrational and Electron Spectroscopy - Experiments and first-principle calculations},
  year         = {2004},
}