The characterisation of chemical species in high temperature lamps

This thesis describes the application of matrix isolation infrared spectroscopy and transpiration techniques to study the chemistry of high temperature lamp systems. Methods used to investigate the chemistry of tungsten halogen and metal halide lamps are reviewed. Matrix isolation techniques and the apparatus developed for the in-situ study of high temperature species are described; the species are formed by passing a reactive gas mixture over a heated metal filament and then trapped for study by matrix isolation infrared spectroscopy. Some theoretical aspects of infrared spectroscopy are discussed, in particular the use of isotopic substitution to determine the shapes of matrix isolated species. The use of spectroscopic data and statistical thermodynamic methods to estimate the bulk thermodynamic properties of vapour phase molecules are also described. The reaction of W or Mo with O2/X2 (X = Cl, Br) or CO2/Cl2 gas mixtures gives MO2X2 as the primary reaction product. Smaller amounts of MOX4 are also formed, although MoOBr4 is not detected. Monomeric MO3 and O3, together with a number of other features believed to be due to polymeric metal oxide species, are observed following the reaction of W or Mo with O2/I2 mixtures. Matrix isolation infrared spectra of the products of the reaction of Cl2 with W can be interpreted in terms of the formation of WCl5 and WCl6. MoCl5 (C4v symmetry) is detected in corresponding Mo/Cl2 experiments and a further absorption band at 433cm-1 is attributed to MoCl4 (Td symmetry) on the basis of observed Mo and Cl isotope patterns. No metal bromides or iodides are detected when these halogen vapours are passed over heated W or Mo filaments. The principal products of the reaction of Cl2 or Br2 with Ta or Nb are the MX5 pentahalides and, for Nb, a smaller amount of the oxyhalides NbOX3. The oxyhalides ReO3X (C3v symmetry) are formed when Cl2 or Br2 is passed over heated Re filaments.