Advanced

Vibrational Spectroscopy of Surface Adsorbates on Metal Surfaces. Experiments and Calculations

Ásmundsson, Ragnar K LU (1999)
Abstract
This work deals with a detailed analysis of the vibrational spectra of methoxy (CH<sub>3</sub>O-) and ethoxy (CH<sub>3</sub>CH<sub>2</sub>O-) on W(110) and Cu(100) single crystal surfaces. By using theoretical <i>ab initio</i> quantum mechanical modeling, it is demonstrated that an unprecedented quantitative understanding of the vibrational frequencies of a surface adsorbate can be obtained. A qualitative understanding of the intensities is also obtained. This was achieved using a simple model in the calculations, where the metal surface was presented with one molybdenum metal atom only. The model was shown to be able to determine small isotopic shifts on both metal surfaces studied, dispite... (More)
This work deals with a detailed analysis of the vibrational spectra of methoxy (CH<sub>3</sub>O-) and ethoxy (CH<sub>3</sub>CH<sub>2</sub>O-) on W(110) and Cu(100) single crystal surfaces. By using theoretical <i>ab initio</i> quantum mechanical modeling, it is demonstrated that an unprecedented quantitative understanding of the vibrational frequencies of a surface adsorbate can be obtained. A qualitative understanding of the intensities is also obtained. This was achieved using a simple model in the calculations, where the metal surface was presented with one molybdenum metal atom only. The model was shown to be able to determine small isotopic shifts on both metal surfaces studied, dispite both material and structural differences in the metal substrates. The isotopic shifts were obtained through <sup>13</sup>C isotopic labeling in ethoxy, using <sup>13</sup>CH<sub>3</sub>CH<sub>2</sub>O-, CH<sub>3</sub><sup>13</sup>CH<sub>2</sub>O- and <sup>13</sup>CH<sub>3</sub><sup>13</sup>CH<sub>2</sub>O-. Once the accuracy of the calculated shifts had been established, it was possible to assign previously undetected vibrational modes in ethoxy-Cu(100) in the C-H stretch region, where the spectra are complicated due to bend overtone interactions with the stretch fundamentals. In addition, the interaction between fundamentals and overtone modes in methoxy, Fermi resonances, is treated using a phenomenological model. Fermi resonances occur when a near accidental degeneracy exists between a fundamental and overtones having the same symmetry, causing the modes to shift away from each other and share intensity. An effective Hamiltonian was used to calculate the Fermi resonance coupling constants through a least-square fitting procedure. This latter treatment reproduces qualitatively the observed intensity redistribution caused by the coupling.



The technique used to record the vibrational spectra was Fourier transform reflection-absorption infrared spectroscopy in the mid-infrared spectral region. This technique does not disturb the surface chemistry and gives the resolution required to be able to resolve the small isotopic vibrational shifts induced by the <sup>13</sup>C labeling. All experiments were performed in a stainless steel ultra high vacuum chamber with a base pressure below 7*10<sup>-11</sup> Torr. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof Friend, Cynthia M., Harvard University
organization
publishing date
type
Thesis
publication status
published
subject
keywords
ab initio electronic structure calculations, Fermi resonance, vibrational spectroscopy, Reflection absorption infrared spectroscopy, Fourier transform infrared spectroscopy, Cu(100) and W(110) single crystal surfaces, Physics, Fysik
pages
45 pages
publisher
Ragnar K. Ásmundsson, Chemical Physics, Lund University
defense location
Getingevägen 60, hall D
defense date
1999-09-10 10:15:00
external identifiers
  • other:ISRN: LUNKDL/NKKF--99/1008--SE
language
English
LU publication?
yes
additional info
Article: I. P. Uvdal, R. Ásmundsson and A.D. MacKerell, Jr. Vibrational Shifts Induced by 13C Isotopic Substitutions in a Surface Adsorbate Determined by Infrared Spectroscopy and Ab Initio Calculations Phys. Rev. Lett. 82 (1999) 125II. R. Ásmundsson and P. Uvdal. Substrate Modification in Vibrational Shifts Induced by 13C Isotopic Substitutions in Adsorbed Ethoxy Determined by Infrared Spectroscopy and Ab Initio Calculations Accepted (1999) in Surf. Sci. Lett.III. R. Ásmundsson and P. Uvdal. Fermi Resonance Coupling in a Surface Adsorbate: The C-H Stretch in Methoxy Adsorbed on Cu(100), Calculations and Experiments Submitted (1999) to J. Chem. Phys.IV. R. Ásmundsson, P.Uvdal and A.D. MacKerell, Jr. Overtone and Combination Modes in the C-H Stretch Region in Ethoxy Adsorbed on Cu(100): Experimental and Calculated Vibrational Spectra In manuscript. The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Chemical Physics (S) (011001060)
id
efdd3b44-1b12-48d4-a591-58f7a8dcffab (old id 39827)
date added to LUP
2016-04-04 10:55:07
date last changed
2018-11-21 21:01:33
@phdthesis{efdd3b44-1b12-48d4-a591-58f7a8dcffab,
  abstract     = {This work deals with a detailed analysis of the vibrational spectra of methoxy (CH&lt;sub&gt;3&lt;/sub&gt;O-) and ethoxy (CH&lt;sub&gt;3&lt;/sub&gt;CH&lt;sub&gt;2&lt;/sub&gt;O-) on W(110) and Cu(100) single crystal surfaces. By using theoretical &lt;i&gt;ab initio&lt;/i&gt; quantum mechanical modeling, it is demonstrated that an unprecedented quantitative understanding of the vibrational frequencies of a surface adsorbate can be obtained. A qualitative understanding of the intensities is also obtained. This was achieved using a simple model in the calculations, where the metal surface was presented with one molybdenum metal atom only. The model was shown to be able to determine small isotopic shifts on both metal surfaces studied, dispite both material and structural differences in the metal substrates. The isotopic shifts were obtained through &lt;sup&gt;13&lt;/sup&gt;C isotopic labeling in ethoxy, using &lt;sup&gt;13&lt;/sup&gt;CH&lt;sub&gt;3&lt;/sub&gt;CH&lt;sub&gt;2&lt;/sub&gt;O-, CH&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;13&lt;/sup&gt;CH&lt;sub&gt;2&lt;/sub&gt;O- and &lt;sup&gt;13&lt;/sup&gt;CH&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;13&lt;/sup&gt;CH&lt;sub&gt;2&lt;/sub&gt;O-. Once the accuracy of the calculated shifts had been established, it was possible to assign previously undetected vibrational modes in ethoxy-Cu(100) in the C-H stretch region, where the spectra are complicated due to bend overtone interactions with the stretch fundamentals. In addition, the interaction between fundamentals and overtone modes in methoxy, Fermi resonances, is treated using a phenomenological model. Fermi resonances occur when a near accidental degeneracy exists between a fundamental and overtones having the same symmetry, causing the modes to shift away from each other and share intensity. An effective Hamiltonian was used to calculate the Fermi resonance coupling constants through a least-square fitting procedure. This latter treatment reproduces qualitatively the observed intensity redistribution caused by the coupling.<br/><br>
<br/><br>
The technique used to record the vibrational spectra was Fourier transform reflection-absorption infrared spectroscopy in the mid-infrared spectral region. This technique does not disturb the surface chemistry and gives the resolution required to be able to resolve the small isotopic vibrational shifts induced by the &lt;sup&gt;13&lt;/sup&gt;C labeling. All experiments were performed in a stainless steel ultra high vacuum chamber with a base pressure below 7*10&lt;sup&gt;-11&lt;/sup&gt; Torr.},
  author       = {Ásmundsson, Ragnar K},
  language     = {eng},
  publisher    = {Ragnar K. Ásmundsson, Chemical Physics, Lund University},
  school       = {Lund University},
  title        = {Vibrational Spectroscopy of Surface Adsorbates on Metal Surfaces. Experiments and Calculations},
  year         = {1999},
}