The infrared band intensities and other properties of the homodimers of the methyl and silyl halides: An ab initio study

The properties of the homodimers of methyl and silyl fluoride, chloride and bromide have been determined by means of ab initio molecular orbital calculations. The interaction energies, molecular structures, vibrational spectra and molecular orbital properties have been investigated, and some common features within each family have been observed. A number of systematic differences in the properties of the dimers have also been noted and rationalized. Typically, discussion of the results of such calculations has focused on the vibrational wavenumber shifts occurring on complexation, and the accompanying changes in the infrared band intensities have received relatively little attention. This paper aims to reposition infrared intensities as valid and useful parameters with which to interpret the formation of the homodimers of polar molecules.

► The properties of the methyl and silyl halide dimers have been computed ab initio.
► The main focus has been on the infrared intensities of the vibrational modes.
► A number of systematic variations in these properties have been observed.
► The intensities of most of the modes show a regular dependence on the halogen atom.