Simulation of IR and Raman spectra based on scaled DFT force fields: A case study of 2-(methylthio)benzonitrile, with emphasis on band assignment

V. Krishnakumar, Gábor Keresztury, Tom Sundius, R. Ramasamy

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171 Citations (Scopus)


The solid phase FT-IR and FT-Raman, solution phase linear dichroism IR (in nematic liquid crystal), and vapor phase GC/IR spectra of 2-(methylthio) benzonitrile have been recorded in the regions 4000-50, 3500-100, 4000-400, and 4000-650 cm-1, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimizations and force field calculations based on density functional theory (DFT) using standard B3LYP/6-31G* and B3LYP/6-311+G* method and basis set combinations. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors yielding fairly good agreement between observed and calculated frequencies. IR dichroism data revealed an error in band assignment associated with a νCS vibration, which could be eliminated only by introducing independent scaling factors for sulfur, whereas the overall frequency fit was further improved. Simulation of infrared and Raman spectra utilizing the results of these calculations led to excellent overall agreement with the observed spectral patterns, especially with the higher level basis set. The SQM approach applying selective scaling of the DFT force field was shown to be superior to the uniform scaling method in its ability to allow for making modifications in the band assignment, resulting in more accurate simulation of IR and Raman spectra including band polarizations and intensity patterns.

Original languageEnglish
Pages (from-to)9-21
Number of pages13
JournalJournal of Molecular Structure
Issue number1-3
Publication statusPublished - Sep 27 2004



  • DFT calculations
  • IR and Raman intensities
  • IR linear dichroism
  • SQM force field
  • Vibrational assignment
  • Vibrational spectra

ASJC Scopus subject areas

  • Analytical Chemistry
  • Spectroscopy
  • Organic Chemistry
  • Inorganic Chemistry

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