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Title: The molecular structures of BrF5 and IF5 ; and vibrational potentials for some spherical top molecules
Author: Heenan, Richard K.
Awarding Body: University of Reading
Current Institution: University of Reading
Date of Award: 1979
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This thesis deals firstly with the calculation of molecular structures for BrFS and IFS' and secondly with anharmonic force field calculations for the spherical top molecules CF4, SiF4, GeF4, SF6 and UF6• In the first part existing gas electron diffraction data for BrFS and 1FS were analysed jointly with microwave rotational constants taken from the literature. Correction terms needed to perform the analyses in terms of the zero point average structure were calculated from harmonic force fields, found by fitting the available spectroscopic data. This part of the work has already been published: R.K. Heenan and A.G. Robiette, J. Mol. Struct. 54 (1979) 135 and 55 (1979) 191. In the second part anharmonic force field refinements were made for spherical top molecules MF4 and MF6 by fitting directly to vibrational wavenumbers and vibration-rotation interaction parameters. Vibrational energies were calculated up to the H40 terms in the Hamiltonian as detailed by Hecht [J.Mol.Spectrosc. 5 (1960) 355]. The calculation of the vibrational matrix elements is discussed using basis functions chosen to transform as irreducible representations of the S4 sub-group of the Td or Dh point groups. Eigenvectors are tabulated for the transformation to a tetrahedral basis as originally given by Hecht. We show that for the molecules chosen here the observed vibrational energies are adequately reproduced by a quadratic force field in curvilinear symmetry force constants together with a Morse potential to describe bond stretching anharmonicity. However for CF4 and SF6 some additional cubic potential constants have been determined. Force fields are reported using data from the literature, including isotopic shifts wherever possible, for gas phase CF4, SiF4, GeF4, SF6 and UF6• Additionally for CF4 and SF6 different effective force fields were determined using liquid 02 or Ar solution data. Fermi resonances were treated by matrix diagonalisation for the interactions (w3-2w4) in CF4 and (ωt -2ω4) in SiF4, This is believed to be the first occasion on which such systems have been treated for triply degenerate vibrations, including overtone and combination bands. Predictions are given for many transitions, including the nV3 manifolds of SF6 and UF6' in order to encourage further experimental work, and to show that vibrational anharmonic splitting energies may be much larger than previously assumed
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available