On the chain length dependence of CH3 vibrational mode relative intensities in sum frequency generation spectra of self assembled alkanethiols

Z. Guo, W. Zheng, Hicham Hamoudi, C. Dablemont, V. A. Esaulov, B. Bourguignon

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

A global modelling of Sum Frequency Generation (SFG) spectra of the self assembly of alkanethiols is presented. All CH modes are modelled together. CH2 modes are assumed local to allow easy calculation of the spectrum as a function of molecular conformation. Ab initio molecular hyperpolarizabilities are used. A phenomenological approach is used to include the Fermi resonance in the model: the calculated intensity of the CH3 symmetric stretch is redistributed according to intensity borrowing by the Fermi resonance. The model is applied to octadecanethiol (ODT) and pentadecanethiol (PDT). The even/odd intensity alternation of SFG CH3 vibrational bands as a function of chainlength is used to test the model. It is found that the relative magnitudes of the hyperpolarizability tensors of the CH3 asymmetric and symmetric modes need to be adjusted. The model provides tilt and twist angles of the alkyl chain in agreement with the literature. It shows that the all trans conformation does not imply the absence of CH2 bands in SFG spectra. In addition, new information is obtained. In particular, if two types of molecular conformations are assumed, the C planes of the two molecules must be perpendicular to each other.

Original languageEnglish
Pages (from-to)3551-3559
Number of pages9
JournalSurface Science
Volume602
Issue number23
DOIs
Publication statusPublished - 1 Dec 2008
Externally publishedYes

Fingerprint

Chain length
vibration mode
Conformations
alternations
Self assembly
Tensors
self assembly
tensors
methylidyne
Molecules
molecules

Keywords

  • Gold
  • Non linear optical methods Sum frequency generation
  • Organo-functionalization of surfaces
  • Self assembly
  • Semi-empirical models and model calculations
  • Thiols
  • Vibrational spectroscopies

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

Cite this

On the chain length dependence of CH3 vibrational mode relative intensities in sum frequency generation spectra of self assembled alkanethiols. / Guo, Z.; Zheng, W.; Hamoudi, Hicham; Dablemont, C.; Esaulov, V. A.; Bourguignon, B.

In: Surface Science, Vol. 602, No. 23, 01.12.2008, p. 3551-3559.

Research output: Contribution to journalArticle

Guo, Z. ; Zheng, W. ; Hamoudi, Hicham ; Dablemont, C. ; Esaulov, V. A. ; Bourguignon, B. / On the chain length dependence of CH3 vibrational mode relative intensities in sum frequency generation spectra of self assembled alkanethiols. In: Surface Science. 2008 ; Vol. 602, No. 23. pp. 3551-3559.
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