Characterisation of Silica and Silicate Nanoparticulate Films using Surface Science Methodologies

Silicate nanoparticles with stoichiometries derived from materials with olivine (Mg_2-xFe_xSiO₄) and pyroxene (Mg_2-xFe_xSi₂O₆) compositions are believed to play a highly significant role in the chemical evolution of the Universe; catalysing the formation of small hydrogen rich molecules and providing a substrate for icy film growth in which complex organic species are ultimately synthesised in the cold, dense environments where stars begin to form. Understanding the surface physics and chemistry of such systems is therefore crucial if we are to understand the chemistry of space.

We will report on preliminary studies of model silica nanoparticulate films produced on a copper substrate by electron beam evaporation in ultrahigh vacuum using a combination of temperature programmed desorption (TPD) and
reflection-absorption infrared spectroscopy (RAIRS) at temperatures down to 18 K. We will describe TPD studies of the distribution of binding energies for CO on these particles and how this can be used to explain inhomogeneous line broadening of the CO RAIR spectra and provide a new window on to the relaxation dynamics of vibrationally excited CO on such nanoparticle surfaces. We will also describe RAIR studies of H₂O diffusion on these particle surfaces and outline our future plans to utilise these small molecules and others (C₂H₂ and C₆H₆) to probe silicate nanoparticles produced by pulsed laser deposition in collaboration with colleagues from the Department of Physics and Astronomy
at the University of Jena.