Laboratory surface and solid state astrochemistry of biomolecular precursors on grain mimics

• Main Author: Abdulgalil, Ali Ghith Moussa
• Other Authors: McCoustra, Martin; McKendrick, Kenneth
• Published: Heriot-Watt University 2013
• Subjects: 523
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.643456

The existence of water (H2O) and acetonitrile (CH3CN) in various extraterrestrial environments attracts considerable attention as both molecules are crucial to understanding the genesis of life. This thesis involves investigations of the physical and chemical interactions of CH3CN and H2O ices condensed on an amorphous silica surface using ultrahigh vacuum-based surface science methods (reflection-absorption infrared spectroscopy, temperature programmed desorption, proton- and electron-irradiation experiments) in an effort to understand how such molecules will behave when they are processed by radiation and heat in space environments. The thermal behaviour of CH3CN on H2O and on the silica surface is governed by a balance of intermolecular forces and shows evidence for wetting of the silica surface (formation of a distinct first adsorption layer before multilayer growth) and of dewetting or island formation on the H2O surface (multilayer growth for all CH3CN exposures). This illustrates the importance of the substrate in determining the solid state growth morphology. Physical and chemical processes induced by 250 to 500 eV electrons have been investigated in the CH3CN and H2O systems. Such interactions promote only desorption from both CH3CN and H2O ice surfaces. 200 keV protons irradiation experiments of CH3CN ices, conducted by collaborators in Italy, in contrast showed evidence for chemical reactions in the solid CH3CN. Quantitative measurements of desorption and reaction cross-sections are used to reconcile this stark contrast. The impact of such processes in relation to H2O on astrophysics is investigated through simple numerical simulations using results derived from this work.