Advanced Photon-In Photon-Out Hard X-ray Spectroscopy

Transcription

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

3 elastic scattering electron nucleus orbit

4 absorption electron nucleus orbit

5 emission from core level electron nucleus orbit

6 emission from valence level electron nucleus orbit

7 inelastic scattering with electronic excitation electron nucleus orbit

8 inelastic scattering with collective excitation electron nucleus orbit

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 1b 2 3a 1 1b 1 4a 1 2b 2

10 The Structure of Liquid Water X-ray Spectroscopy

11 Structure of Liquid Water 0.5 ev reolution Huang et al, PNAS, 106, (2009) Ice spectra from Tse et al, Phys. Rev. Lett. 100: (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 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? current view: slower dynamics in smaller reverse micelles 1-3 however, interfacial water may have weaker hydrogen bonding 1 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 [1] Dokter, A. M.; Woutersen, S.; Bakker, H. J. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, [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,

14 Increased Fraction of Weakened H-Bonds ~ 1000 molecules ~ 300 molecules - 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 Waluyo et al, J. Chem Phys. 131, (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', ~ year old beech, Altmühltal, Germany, leave area ~ 8500 m 2

16 Oxygenic Photosynthesis Where do plants split water? Mn 4 O x Ca 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, (2009)

20 What is the mechanism of photosynthetic oxygen evolution? B. Kok et al. Photochem. and Photobiology 11, 457 (1970) ћω e - ћω O 2 S 0 30 μs S 1 e - ћω S 4 S 2 e - S 3 e - ћω transition times are from Haumann et al. Science 310, 1019 (2005) Currently only S 0 through S 3 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 Nilsson group LBNL, Berkeley SLAC, Stanford

22 THANK YOU

23 X-ray Emission Spectrometer