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

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

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
1b2
3a1
1b1
4a1
2b2

10. The Structure of Liquid Water
X-ray Spectroscopy

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: (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?
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,
[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
- 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, (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 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, (2009)

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

22. THANK YOU

23. X-ray Emission Spectrometer