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Ionization: A key chemical pathway in ices under radiation environment?

Ionization: A key chemical pathway in ices under radiation environment?. Murthy S. Gudipati Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109. Contents. Radiation, Ice and Organic Impurities Ionization - A Quick Tour

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Ionization: A key chemical pathway in ices under radiation environment?

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  1. Ionization: A key chemical pathway in ices under radiation environment? Murthy S. Gudipati Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109

  2. Contents • Radiation, Ice and Organic Impurities • Ionization - A Quick Tour • Highlights of Our Laboratory Discoveries • Solar System Ices under Radiation Environment • Implications to Solar System Icy Surfaces • Implications to Present and Future Missions AcknowledgmentsCollaboration: Louis Allamandola (NASA Ames); John F. Cooper (NASA Goddard); Robert E. Johnson (U. Virginia)Funds: NASA PG&G; PA; DDA; CDAP; Astrobiology; JPL

  3. Radiation, Ice • and • Organic Impurities

  4. Interaction of Radiation and Ice(dissociation & ionization – storage of energy & highly reactive species) Quanta of Energy deposited in ices to heat, dissociate, and ionize molecules in these ices Photons (< 20 eV) : a few events Particles (MeV): 100 to 1000 events Photons - few micronsCosmic Rays ~ meter Energy Storage Charge Storage Chemistry

  5. Building Blocks of Life created / destroyed in Ice Amino Acids from VUV-Irradiated NASA Ames Group (H2O:CH3OH:NH3:HCN = 20:2:1:1)Leiden Group (H2O:CH3OH:NH3:CO:CO2 = 2:1:1:1:1) Micelles from VUV-Irradiated H2O:CH3OH:CO:NH3 Ice Residue (100:50:1:1) [NASA Ames Group] Laser Desorbed Mass Spectra Dworkin et al. Proc. Nat. Acad. Sci.98, 815 (2001); Bernstein et al. Nature416, 401 (2002); Muñoz-Caro et al. Nature416, 403 (2002)

  6. Can Life Evolve and Sustain in Solar System Ices?

  7. Ionization - A Quick Tour

  8. Ionization vs. Dissociation & Excitation High-Energy electron and ion bombardment also results in core-ionization, Auger process etc. (Positive Ion) (Electron) Ionization of Impurities in Ices has not been considered in Astrophysical Sciences until recently!

  9. Ionization vs. Ionic Salts • Ionization: • Forced removal of an electron from a molecule or solid (Workfunction) • Electrons are generated/trapped in ice • Ionic Salts: • Electron is strongly bound to the negative ion of the salt • Hole is similar in both the cases

  10. Ionization Energy in the Gas-Phase Organic Molecules Inorganic Atoms and Molecules are ionized at lower energies than organics

  11. Highlights of Our Laboratory Discoveries

  12. First Direct Evidence for Ionization of PAHs in Ices Polycyclic Aromatic Hydrocarbons (PAHs) - Abundant in Space Highlights • High ionization yields • Electron injection into the ice • Low ionization energy (2 eV less from gas-phase) • Stability of ions up to 120 K • Low-energy multiple ionizations • Electron mobility 4.0 eV Gudipati & Allamandola, ApJ Letters 615 (2004) L177

  13. Organic Chemistry in Ices after Ionization Multiple oxidation and hydrogenation reactions result in Ketones, Alcohols, Ethers, … Bernstein, Sandford, Allamandola, Seb Gillette, Clemett, Zare, Science 283, 1135 (1999)

  14. Solar System Ices under Radiation Environment

  15. Solar Radiation Reaching Ices on Earth and Mars Mars Surface & Upper Atmosphere Earth Surface & Upper Atmosphere IEICE = (IEgas - 2.0) eV Atoms & molecules with IEgas < 6 eV on Earth & IEgas < 8 eV on Marsare ionized when imbedded in ice surface < 6 eV < 4 eV

  16. Outer Solar System Ices • Jovian and Saturnian Icy Bodies: • keV to MeV electrons & ions • Hard UV Solar radiation penetration due to lack of atmosphere (except Titan)

  17. Example: Europa under Jovian Magnetospheric Radiation Jupiter’s magnetospheric electrons bombard exclusively trailing hemisphere of Europa, creating a possible charge gradient on Europa’s hemispheres.

  18. Ionization in IcesBiological & Environmental Importance In ices some of these atoms and molecules may be ionized with ~300 nm UV-B sunlight Chlorophyll

  19. Implications to Solar System Icy Surfaces

  20. Outer Solar System Ices containing Impurities Complex & neutral Molecules created and destroyed continuously Chart: W. M. Grundy, M. W. Buie, J. A. Stansberry, J. R. Spencer, and B. Schmitt, Icarus 142, 536–549 (1999) Increase in Chemical Reactivity Ions & Radicals stored in frozen Ices

  21. Organics in Martian and Polar Ices • Organics in Martian Ices: • Under ultraviolet (UV < 200 nm) radiation, hydrocarbons in Martian ice surfaces can be quickly oxidized. As a result alcohols and other oxygen-rich organics can be produced, which degrade into small molecules, or finally perhaps to CO2. • Organics in Polar Ices on Earth: • Anthropogenic PAHs are detected to be drifting to the polar regions and deposit onto the polar ices. UV (< 300 nm) radiation can ionize large PAHs in polar ice surfaces leading to the formation of oxidized PAhs. Indeed oxidation products of PAHs are seen in polar ices.(Grannas, A. M., et al., 2007. An overview of snow photochemistry: evidence, mechanisms and impacts. Atmospheric Chemistry and Physics. 7, 4329-4373).

  22. Implications to Present and Future Missions

  23. Missions

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