The temperature dependence of the molecular structure parameters in SF6

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Abstract
The importance of anharmonic vibrational effects in SF6 has been demonstrated by the dependence of the molecular structure on temperature. The apparent interatomic distances and mean vibrational amplitudes were measured in the temperature range between 200 and 500 K and compared with existing theories. Though the mean amplitudes were found to be well modeled by the usual normal coordinate analysis, the increase with temperature of the apparent interatomic distances was found to be significantly greater than predicted either by harmonic normal mode analysis or the Morse potential function. However, the combination of these approximations describes the experimental results quite well. Inclusion of stretching anharmonicity, nonbonded fluorine repulsions, and stretch–bend interactions in a modified Uray–Bradley potential also gives agreement for the bonded distance. However, the dependence on the temperature of the nonbonded distances is at present not adequately accounted for.