1 / 24
Télécharger la présentation

By Chris Bennett

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Design of a Novel Ultra High Vacuum Surface Machine to Determine the Formation of Glycolaldehyde in the Interstellar Medium By Chris Bennett

  2. Synopsis • An introduction to Astrochemistry. • How glycolaldehyde may be formed in the interstellar medium. • Overview of the machine design.

  3. Why Study Astrochemistry? • To increase our understanding of molecular processes. • Origin of life on Earth. • Possibility of finding life in an extraterrestrial environment.

  4. The Discovery of Sugar in Space

  5. Details of the Discovery • Found in Hot Core Sagittarius B2(N-LMH). • Detected by NRAO 12m telescope in microwave region. • Glycolaldehyde is the simplest sugar. Glycolaldehyde

  6. The Origin of Life on Earth? • The origin of life on this planet took place in under 300 million years. • Miller-Urey experiment does not produce sugars. • Developments on Boutlerow’s formose reaction are also very unlikely. • However, sugar has been found in space and meteorites such as Murchison and Murray.

  7. How do they detect molecules in space? • For solid state, compare IR spectrum to that of black body radiation. • These IR absorptions correspond to stretching and vibration modes of a molecule. • Gas phase species can be identified from transitions in rotational modes in the microwave region.

  8. Problems with Current Models • Astrochemical kinetic models based on gas phase kinetics cannot explain the observed column densities for C2H4O2 species. Glycolaldehyde Acetic acid Methyl formate

  9. Interstellar Grains • The interstellar medium is full of icy grains. • It is possible that glycolaldehyde is formed within cold molecular clouds, on the surface of grains. • Models which account for surface-grain reactions don’t work either.

  10. Overcoming Energy Barriers at 10 K

  11. The Effects of Ultraviolet Radiation on Interstellar Ices • UV light is absorbed within the first few monolayers of the ice. • Each photon can only interact with a single molecule. • This can lead to homolytic bond cleavage, producing suprathermal radicals.

  12. Example

  13. The Effects of Cosmic Ray Bombardment of Interstellar Ices • Predominantly H+ and He2+ ions (1-10 MeV). • Reactions can take place by three mechanisms: i) Hydrogen abstraction ii) Insertion into a σ bond iii) Addition to a π or non-bonding orbital

  14. Examples

  15. Synthesis of Glycolaldehyde in the Interstellar Medium • A systematic retrosynthetic analysis of glycolaldehyde was produced. • A similar scheme was also produced for methyl formate and acetic acid. • This showed what experiments need to be carried out.

  16. Designing a Machine to Carry Out the Surface Experiments • This machine must mimic the conditions in the interstellar medium. • Pressure – Interstellar pressure ~ 10-12 mbar. • ii) Temperature – Cold molecular cloud ~10 K, hot molecular core ~300 K.

  17. iii) Icy grains – Will use binary mixtures of molecules identified in the solid state. iv) Radiation sources - UV light, electrons & cosmic rays all need to be simulated. The need for a differentially pumped region. •An interlock system must also be in place for safety.

  18. Identification of Products • Detection of newly formed molecules within the ices by AR-FTIR spectroscopy in situ. • Gas phase species will be identified by a quadrupole mass spectrometer.

  19. The Calculations for the Differential Chambers • Using a worst case scenario of the initial proposed set-up, calculations of the pressure in the main chamber during ion bombardment was carried out using the following equations:

  20. Results •A Vacuum of 10-11 mbar can be achieved.

  21. Overview of Final Design (Top View)

  22. Overview of Final Design (South View)

  23. Outlook • The retrosynthetic analysis revealed what experiments need to be done. • The machine has been designed and proven to be able to operate at the desired pressure. • On completion of the experiments, new kinetic data can be added to the astrochemical models which should account for the observed number densities.

  24. References General information • Final project report and references within. Picture of Sagittarius B2 taken from: • http://home.intekom.com/franlet/page377.htm Picture of IR identification adapted from: • d'Hendecourt, L., Dartois, E. 2001. Spectrochimica Acta Part A. Vol. 57, pp 669-684.

More Related