Joint local- and normal-mode studies of the overtone spectra of the methyl halides: CH3F, CH3Cl, CH3Br, CD3Br, and CH3I

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Abstract

The infrared spectra of CH3F, CH3Cl, CH3Br, and CH3I have been investigated in the range 2500-16 500 cm(-1) and that of CD3Br in the range 2000-7000 cm(-1). New experimental data are reported for CH3F and CD3Br and these data together with existing literature data for CH3Cl, CH3Br, and CH3I have been analyzed in terms of a hybrid local-mode/normal-mode model. Local-mode basis functions have been used for the C-H(D) stretching vibrations and normal-mode basis functions to describe the C-H(D) bending vibrations. This joint approach, which also takes account of Fermi resonances, enabled the determination of stretch/bend anharmonicity and Fermi-resonance parameter sets which reproduce the observed data over wide energy ranges and compare much more favorably with literature ab initio results than previous parameter sets. The analyses have lead to a new vibrational assignment in CH3Cl and two corrected band centers in CH3Br and CH3I and predictions of unassigned bands raise several challenges to experiment. (C) 1999 American Institute of Physics. [S0021-9606(99)01046-6].

Original languageEnglish
Pages (from-to)10021-10033
Number of pages13
JournalThe Journal of Chemical Physics
Volume111
Publication statusPublished - 1999

Keywords

  • ANHARMONIC-FORCE FIELDS
  • VIBRATIONAL ANHARMONICITY
  • STRETCHING VIBRATIONS
  • HIGH-RESOLUTION
  • INFRARED BANDS
  • BROMIDE
  • FERMI
  • (CH3F)-C-12
  • INTENSITIES
  • DERIVATIVES

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