Combined far infrared RAIRS and XPS studies of TiCl4 adsorption and reaction on Mg films

In recent years there has been an increase in interest in the study of model Ziegler-Natta catalysts used for the polymerisation of ethene and propene. Particular attention has focused on catalysts consisting of TiCl4 on activated MgCl2 accompanied by a co-catalyst, usually triethylaluminium (AlEt3). As part of a wider project on the characterisation of model Ziegler-Natta catalysts we have investigated the interaction of TiCl4 with metallic Mg films grown on a Au surface using X-ray photoelectron spectroscopy (XPS) and far infrared reflection absorption infrared spectroscopy. Somewhat surprisingly, the infrared spectra show little variation as a function of exposure to TiCl4. A very broad asymmetric vibrational band grows in with maximum intensity at 382 cm−1. Three prominent low frequency shoulders are observed at approximately 360, 320, and 260 cm−1. For monolayer coverages of Mg the main band at 382 cm−1 is narrower, less asymmetric and accompanied by a prominent shoulder at 398 cm−1, which increases with increasing exposure to TiCl4. TiCl4 exposure in the presence of 5 × 10−8 Torr of ethyl benzoate results in a change in line shape with low frequency broadening and a small shift in the frequency of the band. These spectra are discussed in the light of the possible constituent species making up the surface layer.