1. School of Chemistry, University of Nottingham 1 Meteorite Nanoparticles as Models for Interstellar Grains: Synthesis and Preliminary Characterisation M. N. Mautner, V. Abdelsayed and M. S. El-Shall Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284, USA J. D. Thrower, S. D. Green, M. P. Collings and M. R. S. McCoustra School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK

2. School of Chemistry, University of Nottingham 2 The Nature of Interstellar Dust  Observational evidence for two grain chemistries –Carbonaceous Materials 217 nm “bump” in interstellar extinction IR observations of aromatic C-H stretching modes around 2.8 to 3.7  m and ring modes at longer wavelength –Silicate Materials IR observations of Si-O stretching modes around 10  m Far-IR bands of silicates Most laboratory studies of gas-grain interactions have focussed on the carbonaceous materials as we have a good surface science model in HOPG, our purpose is to develop a chemically and morphological realistic model for the silicate materials.

3. School of Chemistry, University of Nottingham 3 The Silicate Dust Model  Laser Vaporisation/ Controlled Condensation (LVCC) using powder from meteorites (Murchison and Allende) to mimic chemical composition  Relatively high density gas phase results in rapid vapour plume cooling and condensation of nanoparticles

4. School of Chemistry, University of Nottingham 4 The Silicate Dust Model  Morphology of nanoparticles akin to that of interplanetary dust particles, currently our best model for interstellar grains  Await the results of the Stardust mission with interest.

5. School of Chemistry, University of Nottingham 5 The Silicate Dust Model  Infrared spectroscopy of the materials is consistent with observations of dusty regions such as W33A. W33A LVCC on Murchison Material LVCC on Allende Material

6. School of Chemistry, University of Nottingham 6 The Silicate Dust Model  Preliminary studies of the interaction of CO with thin nanoparticle films yields –Growth of broad RAIR feature at 2140 cm -1 until normal solid CO LO-TO split absorption is observed at multilayer coverages –Linewidth reflects surface heterogeneity and so studies on nanoparticles with simpler composition are warranted –No evidence for any other bands

7. School of Chemistry, University of Nottingham 7 The Silicate Dust Model  Preliminary studies of the interaction of CO with thin nanoparticle films yields –TPD shows a sub-monolayer feature that grows in without moving to lower maximum temperature –Nanoporosity, cf. ballastically deposited pASW, is short range –CO Binding energy estimated to be 13.5±3 kJ mol -1 cf. 9.8± 0.2 kJ mol -1 on water ice and ca. 6 kJ mol -1 on CO ice

8. School of Chemistry, University of Nottingham 8 Acknowledgements Professor Samy El-Shall and Dr. Michael Mautner (VCU) Dr. Mark Collings Simon Green and John Thrower ££ NASA PPARC and EPSRC Leverhulme Trust University of Nottingham ££