Uwe BergmannLinac Coherent Light Source

SLAC National Accelerator Laboratory

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

bergmann@slac.stanford.edu

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

sampledetector

monochromator

Photon-in Photon-out X-ray Spectroscopy

electron

nucleusorbit

elastic scattering

electron

nucleusorbit

absorption

electron

nucleusorbit

emission from core level

electron

nucleusorbit

emission from valence level

electron

nucleusorbit

inelastic scattering with electronic excitation

electron

nucleusorbit

inelastic scattering with collective excitation

the hydrogen bond is directionalprobing of valence electrons

local structure of water configurations

Probing Valence Electrons

4a1

2b2

1b2 1b13a1

occupied

unoccupied

molecular orbitals of the water molecule

The Structure of Liquid Water

X-ray Spectroscopy

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