The anharmonic potential energy surface of methyl fluoride

I. A. Atkinson, Mark McGregor Law

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

A large experimental spectroscopic data set sensitive to the cubic anharmonic potential energy surface (PES) of methyl fluoride has been compiled from the literature for six symmetric and asymmetric top isotopomers of methyl fluoride: (CH3F)-C-12, (CH3F)-C-13, (CD3F)-C-12, (CD3F)-C-13, (CHD2F)-C-12 and (CH2DF)-C-12. This empirical data set has been used to critically assess the best available literature ab initio cubic force field and various 'improved' theoretical force fields. A perturbation-resonance approach to the calculation of the observables from the force constants has been utilized and existing PESs were found to reproduce the data poorly. The careful treatment required for the correct theoretical reproduction of empirical spectroscopic constants arising from highly correlated least-squares fits to the original data is discussed. A new fit to the data has been performed (optimising 19 of the 38 cubic force constants) resulting in a much improved PES, The latter has been used to predict currently unknown spectroscopic constants for the least well-characterised isotopomer (CH2DF)-C-12. The prospects for a future empirical determination of the complete cubic force field of methyl fluoride are discussed and new data most likely to yield new information on the PES identified. (C) 2002 Elsevier Science B.V. All rights reserved.

Original languageEnglish
Pages (from-to)873-885
Number of pages12
JournalSpectrochimica Acta Part A
Volume58
DOIs
Publication statusPublished - 2002

Keywords

  • potential energy surface
  • polyatomic molecules
  • isotopomers
  • anharmonic
  • methyl fluoride
  • spectroscopic data
  • BORN-OPPENHEIMER APPROXIMATION
  • 2ND-ORDER CORIOLIS RESONANCE
  • VIBRATION-ROTATION LEVELS
  • FORCE-FIELD
  • SPECTROSCOPIC ACCURACY
  • MICROWAVE SPECTROSCOPY
  • ROVIBRATIONAL ANALYSIS
  • INFRARED-SPECTRA
  • OVERTONE SPECTRA
  • LEAST-SQUARES

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