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Uwe Bergmann Linac Coherent Light Source SLAC National Accelerator Laboratory PowerPoint Presentation
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Uwe Bergmann Linac Coherent Light Source SLAC National Accelerator Laboratory

Uwe Bergmann Linac Coherent Light Source SLAC National Accelerator Laboratory

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Uwe Bergmann Linac Coherent Light Source SLAC National Accelerator Laboratory

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  1. FLS 2010, ICFA Beam Dynamics Workshop, SLAC, Menlo Park, CA, March 2, 2010 ħω ħω’ e- Advanced Photon-In Photon-Out Hard X-ray Spectroscopy Uwe Bergmann Linac Coherent Light Source SLAC National Accelerator Laboratory bergmann@slac.stanford.edu

  2. monochromatic analyzer (Rowland geometry) monochromator X-ray beam detector sample dispersive analyzer (e.g. von Hamos geometry) monochromator X-ray beam PSD sample Photon-in Photon-out X-ray Spectroscopy

  3. elastic scattering electron orbit nucleus

  4. absorption electron orbit nucleus

  5. emission from core level electron orbit nucleus

  6. emission from valence level electron orbit nucleus

  7. inelastic scattering with electronic excitation electron orbit nucleus

  8. inelastic scattering with collective excitation electron orbit nucleus

  9. Probing Valence Electrons the hydrogen bond is directional probing of valence electrons local structure of water configurations molecular orbitals of the water molecule occupied unoccupied 1b1 1b2 3a1 4a1 2b2

  10. X-ray Spectroscopy The Structure of Liquid Water

  11. Structure of Liquid Water 0.5 eV reolution Huang et al, PNAS, 106, 15214–15218 (2009) Ice spectra from Tse et al, Phys. Rev. Lett. 100: 095502 (2008)

  12. Suggested Model of Water based on Combination of SAXS, XES and XRS Disordered ‘soup’ Ice like patches ~10-15 Å • - On the time-scale of the scattering and spectroscopic processes two local structural species coexist with tetrahedral-like patches of dimension of order 10-15 Å in dynamic equilibrium with H-bond distorted and thermally excited structures. • - Both the characteristic dimension based on SAXS and the local structure of the tetrahedral-like component based on XES/XRS are relatively insensitive to temperature whereas that of the H-bond distorted component continuously changes as it becomes thermally excited and expands, leading to loss of contrast in SAXS. • The tetrahedral-like patches form as low energy-low entropy structures of lower density. The higher density, thermally excited H-bond distorted structure is a high entropy structure. • - The detailed structure of the two types of species and the time-scale on which these fluctuations exist are not yet determined.

  13. Water in Reverse Micelles • model system for confined water • how does confinement change the hydrogen bonding network of water? • different types of water in reverse micelles • surface water molecules are immobilized by hydrophilic head group (“interfacial water”) • water molecules in the core behave like bulk water (“core water”) • most existing studies are based on vibrational spectroscopy • current view: slower dynamics in smaller reverse micelles1-3 • however, interfacial water may have weaker hydrogen bonding1 [1] Dokter, A. M.; Woutersen, S.; Bakker, H. J. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 15355-8. [2] Tan, H.; Piletic, I. R.; Riter, R. E.; Levinger, N. E.; Fayer, M. D. Phys. Rev. Lett. 2005, 94, 1-4. [3] Piletic, I. R.; Tan, H. S.; Fayer, M. D. J Phys Chem B 2005, 109, 21273-21284.

  14. Increased Fraction of Weakened H-Bonds - Increase in pre-edge - Slight decrease in post-edge • Spectral changes are consistent with the increase of weakened H-bond species (similar as increasing the temperature) • More broken hydrogen bonds (consistent with Dokter et.al.) • More structured water as suggested by some from slower dynamics (vibrational study) can be excluded ~ 1000 molecules ~ 300 molecules Waluyo et al,J. Chem Phys. 131, 031103 (2009)

  15. Oxygenic Photosynthesis photosynthesis:- only fundamental source of food on earth - has created our atmosphere and ozone layer - has created fossil energy sources (crude oil, coal, gas)- shows alternative ways to obtain energy in the future! ‘Bavaria Buche', ~ 500-800 year old beech, Altmühltal, Germany, leave area ~ 8500 m2

  16. Oxygenic Photosynthesis Where do plants split water? Mn4OxCa cluster

  17. Kok Cycle of Water Splitting B. Kok et al. Photochem. and Photobiology 11, 457 (1970)

  18. Calculated valence to core spectra for Fe(IV)-O and Fe(IV)-OH Compound II derivatives Lee et al, submitted

  19. O-Mn Crossover XES in PSII Pushkar et al, Angew. Chem. Int. Ed. 48, 800-803 (2009)

  20. ћω e- ћω S1 S0 O2 30 μs e- 70 μs ћω 1.3 ms S2 S4 190 μs e- e- S3 ћω What is the mechanism of photosynthetic oxygen evolution? B. Kok et al. Photochem. and Photobiology 11, 457 (1970) transition times are from Haumann et al. Science 310, 1019 (2005) Currently only S0through S3 states can be trapped

  21. Conclusions and Future Photon-in photon-out hard x-ray spectroscopy requires very intense sources , we just scratching the surface New sources and instruments needed to use the full potential of these powerful techniques New sources will help to answer: What is the structure of water? How do plants split water? Thanks to: Yachandra group LBNL, Berkeley Nilsson groupSLAC, Stanford

  22. THANK YOU

  23. X-ray Emission Spectrometer