Uwe Bergmann Linac Coherent Light Source SLAC National Accelerator Laboratory ħω e - ħω’ Advanced Photon-In Photon-Out Hard X-ray Spectroscopy [email protected] FLS 2010, ICFA Beam Dynamics Workshop, SLAC, Menlo Park, CA, March 2, 2010
Jan 17, 2016
Uwe Bergmann
Linac Coherent Light Source SLAC National Accelerator
Laboratory
ħω e-ħω’
Advanced Photon-In Photon-Out Hard X-ray Spectroscopy
FLS 2010, ICFA Beam Dynamics Workshop, SLAC, Menlo Park, CA, March 2, 2010
dispersive analyzer (e.g. von Hamos geometry)
PSD sample
monochromator
X-raybeam
monochromatic analyzer (Rowland geometry)
X-ray beam
sample
detector
monochromator
Photon-in Photon-out X-ray Spectroscopy
electron
nucleusorbit
inelastic scattering with electronic excitation
electron
nucleusorbit
inelastic scattering with collective excitation
the hydrogen bond is directional
probing of valence electrons
local structure of water configurations
Probing Valence Electrons
4a1
2b2
1b2 1b13a1
occupied
unoccupied
molecular orbitals of the water molecule
Ice spectra from Tse et al, Phys. Rev. Lett. 100: 095502 (2008)
Structure of Liquid Water0.5 eV reolution
Huang et al, PNAS, 106, 15214–15218 (2009)
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.
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 micelles1-3
• however, interfacial water may have weaker hydrogen bonding1
• 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, 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.
- 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
Increased Fraction of Weakened H-Bonds
~ 1000 molecules~ 300 molecules
Waluyo et al, J. Chem Phys. 131, 031103 (2009)
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
Where do plants split water?
Mn4OxCa cluster
Oxygenic Photosynthesis
B. Kok et al. Photochem. and Photobiology 11, 457 (1970)
Kok Cycle of Water Splitting
Calculated valence to core spectra for Fe(IV)-O and Fe(IV)-OH Compound II derivatives
Lee et al, submitted
O-Mn Crossover XES in PSII
Pushkar et al, Angew. Chem. Int. Ed. 48, 800-803 (2009)
ћω
S0
S3
S1
S2S4
e-
e-
e-e-
O2 30 μs 70 μs
190 μs
1.3
ms
ћω
ћω
ћω
transition times are from Haumann et al. Science 310, 1019 (2005)
B. Kok et al. Photochem. and Photobiology 11, 457 (1970)
Currently only S0 through S3 states can be trapped
What is the mechanism of photosynthetic oxygen evolution?
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?
Conclusions and Future
Thanks to:
Yachandra group LBNL, Berkeley
Nilsson group SLAC,
Stanford
THANK YOU
X-ray Emission Spectrometer