Introduction to X-ray

Spectroscopy

Pieter Glatzel

Books

J. J. Sakurai:

“Advanced Quantum Mechanics”

Addison Wesley, 1967

G. Bunker:

“Introduction to XAFS”

Cambridge Press, 2010

F.M.F. de Groot and A. Kotani:

“Core level spectroscopy of solids”

Taylor and Francis, 2008

W. Schülke:

“Electron Dynamics by Inelastic X-ray

Scattering”

Oxford University Press, 2007

Michel van Veenendaal:

“Theory of Inelastic Scattering and

Absorption of X-rays”

Cambridge University Press, 2015

Reminder: The photon

hchE

Energy

0 100 000 eV5 eV 100 eV 1000 eV1 eV

4

Linear momentum

2, kkp

Photon intrinsic angular momentum

5Wikipedia

Energy

0 100 000 eV

Infrared

VUV

Raman

Soft X-ray Hard X-rayUV-Vis

5 eV 100 eV 1000 eV1 eV

Vibration

Valence shell Core levels

The response of the system that is probed by photons

depends on the photon energy.

6

Spectroscopy

What may happen in the sample?

h

1s

3d

EF

A single electron energy diagram is simple and qualitative.

A simplified view: An electron is excited to an unoccupied orbital.

2p

Electronic and atomic structural information

Element specific

Bulk sensitive; compatible with

in-situ and extreme conditions

XAS XES

Why X-ray Spectroscopy

Soft X-Rays Hard X-Rays

Soft and hard X-rays to study electronic structure

Tender X-rays

Ideal for electronic structure studies Ideal for in situ studies

Improve in situ conditions Develop new techniques to study electronic structures

L- and K-edges in 3d transition metals

10 Gilbert et al., J. Phys. Chem. A, Vol. 107, No. 16, 2003

2p → 3d 1s → np

Soft X-rays Hard X-rays

Why X-ray spectroscopy?

11

Spectroscopy does not require long range order.

Ideal tool for e.g. catalysis, environmental sciences, biology, …

Identify Cr(V)…

J. Bagar et al., SSRL

Electromagnetic radiation

trkieAA

ˆ0

Interaction of X-rays with matter

Describe photon with vector field:

q

q: scattering angle

kin-kout=q (momentum transfer)

in-out (energy transfer)

q

In first order, a term in

A2 is retained.

In second order, a term in

A∙p is retained.

A

)ˆ,,( outoutout k

)ˆ,,( ininin k

Perturbation Theory

Perturbation Theory: Two scattering terms

2A

Ap

)ˆ,,( ininin k

)ˆ,,( outoutout k

n

The A2 term and the dynamic structure factor

Thomson scattering: in=out

Bragg scattering: in=out

Raman scattering: out<in

Compton Scattering: out<in

q

with

outin

i

rqikkqeO i

;ˆ

)ˆ,,( outoutout k

)ˆ,,( ininin k

Dynamic Structure Factor

f

outingfoutin

in

outoutin EEgOfF

2* ˆ),(

THE RESONANT SCATTERING TERM: XES, RXES, RIXS, RXRS, HERFD

Perturbation Theory: Two scattering terms

2A

Ap

)ˆ,,( ininin k

)ˆ,,( outoutout k

n

The A∙p term

(resonant) X-ray emission

(RXES, RIXS, fluorescence, XAS)

q

Kramers and Heisenberg

f

outingf

n ningnin

outoutin

KH EEiEE

gOnnOfF

2† ˆˆ

),(

)ˆ,,( outoutout k

)ˆ,,( ininin k

...))(ˆ(ˆ

ˆ

rkrr

epOj

rki

jj

1s13dn+1

3p53dn+1

1s13dnp

3p53dnp

Tota

l En

ergy Kb

EF

1s

2p

3p

3d3d

nKb rKb

One-electron diagram Many body diagram

Transition schemes

1s23dn

Energy scheme and spectroscopy

Total

Energy

FeIII [Ar 3d5]

1s13d5(p)1

2p53d5(p)1

1s13d6

3d6MOn-1

|g>

|<n|Ô|g>|2

in

2p53d6

3p53d5(p)1

3p53d6

M-edge

Ka

Kb

Valence-to-core

UV-Vis

L-edge

out

|n>

HEtotalˆ

Single crystal

monochromator

Ei, I0

Sample

Ei, I1

Ee, I21

0ln)(I

IEi

2)( IEi

Photon-in/photon out spectroscopy

Fluorescence

Single crystal

monochromator

Ei, I0

Sample

Ei, I1

Ee, I2

Analyzer crystal

1

0ln)(I

IEi

X-ray Emission

Photon-in/photon-out spectroscopy

Fluorescence

2)( IEi

ESRF ID26

)ˆ,,( outoutout k

)ˆ,,( ininin k

What can inner-shell spectroscopy do?

Inner-shell spectroscopy probes electronic transitions and thus the electron

density or electron configuration. This may tell you about:

• The chemical environment

o bond distances

o bond angles

o type and number of ligands

• The spin-orbit term of the ground state: The measured spectrum represents

excited states that are linked to the ground state via the transition matrix

element. The transition probability depends on the ground state symmetry,

e.g. the spin state, formal oxidation state

|g>

|n>

1S

1P2S+1L

DS=0

DL=0;±1

What is oxidation state: Atoms and electron density

When “measuring” oxidation state we often ask “what is the charge per atom?”

2r(r) and MO in a Ni complex

Is that the right question to ask?

The idea of an atom

Wikipedia:

“Noumenon: An object knowable by the mind or intellect, not by the senses;”

… a noumenon in the sense of Kant.

… an experimentalist has no doubt that he or

she is measuring the properties of a single

atom…

Orbital relaxation

All electrons will adjust after excitation with X-rays:

Always consider ALL electrons when describing the energy levels.

The potential experienced by all electrons changes after photoexcitation.

Two-electron excitation

Valence Orbital

Empty Orbital

The orbitals may adjust non-adiabatically, i.e. electrons are excited to higher orbitals

upon orbital relaxation (additionally to the electron that is photo-excited).

The inner-shell absorption proces

Energy

g

n

T lcaabs OSgOn r 2

2

0

2

Many-electron

wavefunction

One-electron

wavefunction

≈ 3d6

≈ 1s13d64p1

≈ 1s → 4p

h

Approximate multi-

electron effects by

scaling factor S02

Electronic structure calculations and inner-shell spectroscopy

Ligand field multiplet theory

Start with ion in spherical symmetry

Branch to real symmetry

Include covalency using

configuration interaction (CI)

Good treatment of core hole effect

and multi-electron excitation

Electron density calculations

Start with structure

Include core hole

Include multi-electron excitations

Good treatment of ligands/long

range order

1

N!

1(r

1 ) 1( r

2 ) 1(r

N )

2( r

1)

N ( r

1 ) N ( r

N )

empirical

approximative

(e.g. to Oh)

Multi-electron excitations

Multi-electron

excitation

Experiment: Ce L3 (2p3/2) edge

One-electron calculationSingle impurity Anderson model

~f0~f1

No multi-electron excitations

Correct crystal field splitting

Multi-electron excitations

Empirical crystal field splitting

EXPERIMENTAL ARTEFACTS

Secondary process detection

t

dA

XESA

eEKII

t

1

sin

)(0

sin

)(

sin

)( Fttt

EEA

lsdscsfsfJK

4

J jumping ratio – PE of shell of interest

fluorescence yield per shell

f fractional yield per subshell

fs fraction of line measured with spectrometer

cs crystal efficiency

ds detector efficiency

ls losses due to absorption (windows, beam path in air)

The goal is to determine (E) by recording the intensity of the scattered X-rays

Selective fluorescence detection in CoFe2O4

Total fluorescence

yield

Fe fluorescence

yieldt

dA

XESA

eEKII

t

1

sin

)(0

The total absorption appears in the denominator

TFY and HERFD on CoFe2O4

Total fluorescence

yield

Fe fluorescence

yield

Experiment

Calculation using tabulated values

after edge

before edge

J. Synchrotron Rad. (2012). 19, 911–919

Incident Beam Self Absorption

Incident Beam Self Absorption

compresses the intensity of a

spectrum

Incident beam self absorption (IBSA) arises from a similar mechanism as the

dip seen in the previous slides but for the same element.

36

RADIATION DAMAGE

If a leaf can do it, we can do it too!

Lubitz and Messinger, Energy and Environmental Science, 2008

Photosynthesis

The Sample

Spinacia oleracea

Photosystem IIMulti-protein complex Photosystem-II

Damage of the Mn cluster

41

6540 6550 6560 6570Incident Energy [eV]

Dealing with radiation sensitive samples on ID26

Page 42

Spectral change at fixed energy as function of time.

beam size: 700 x 100 m; ~2*1013 photons/second

Dealing with radiation sensitive samples

l Title of Presentation l Date of Presentation l AuthorPage 43

Each energy point measured in

different position of beam on

sample.

Take map of metal

fluorescence response.

Science 316, 1444-1448 (2007); Nature 406, 752-757 (2000)

Detect and Destroy at a free electron laser

Kern et al. Science 340 (2012) 491

PSII and the free electron Laser

XFEL provides correct Kb spectra

Kern et al. Science 340 (2012) 491

1s

2p

3p

VS

THE ENERGY LEVELS OF LOCALIZED ORBITALS

3d orbitals in a crystal field

48

10Dq

atomict2g

eg

Oh

Octahedral and tetrahedral coordination

49

ChemWiki @ UC Davis

3d orbitals in a crystal field

50

ChemWiki @ UC Davis

MULTIPLET THEORY

An open shell

Et = Erest + E3d

Et =Erest + ?

How can we treat open shells ? → MULTIPLET THEORY

3d orbitals

Treating electron-electron interactions

j>i

j>i

ij

ji|g|ijij|g|ij

|g|

"direct term" > 0 "exchange term" > 0

Matrix element for two-electron operator:

“Slater integrals or Racah parameters”

gijj1

i1

g( ri

i j

i 2

N

, rj

)two-electron operator:

An open shell: 3d2

40

221

2121

21

L

ll

llllL

llL

The Racah parameters determine the magnitude of the splitting.

Angular momentum coupling

(Total Angular Momentum)

(for d-electrons)

(S,P,D,F,G)

d2

3F

1D3P

1G

1S

Notation: 2S+1L

Crystal Field Splitting: Tanabe-Sugano diagram

Atom Oh coordination

Additional splitting due to orbital hybridization (ligand field theory)

→ The spectra become very very complex already for d2

d2

3d

t2g

eg

Inner-shell spectra are often very complex

56

Intra-valence shell electron-electron interactions

Core hole – valence electron interactions

Multi-electron excitations

3d5

2p5

RESONANT INELASTIC X-RAY SCATTERING: RIXS, HERFD

Hard X-ray Photon-in/Photon-out spectroscopy

Single crystal

monochromator

Ei, I0

Sample

Ei, I1

Ee, I2

I2~ (Ei)

1

0ln)(I

IEi

Incident Energy (Ei) [eV]

Ee

2p

3d

4f5d

Ei

2p

3d

4f5d

Second order process

Correctly treated with

Kramers-Heisenberg equation

CeO2

L3-edge

Hard X-ray Photon-in/Photon-out spectroscopy

Single crystal

monochromator

Ei, I0

Sample

Ei, I1

Ee, I2

Ee

2p

3d

4f5d

I2~ (Ei)

1

0ln)(I

IEi

Incident Energy (Ei) [eV]

Analyzer crystal

Energy Transfer (Ei-Ee) [eV]

XES

Ei

2p

3d

4f5d

XAS

Hard X-ray Photon-in/Photon-out spectroscopy

Single crystal

monochromator

Ei, I0

Sample

Ei, I1

Ee, I2

I2~ (Ei)

1

0ln)(I

IEi

Incident Energy (Ei) [eV]

Analyzer crystal

Energy Transfer (Ei-Ee) [eV]

XAS

CeO2 XAS

TFY

HERFD

Conventional TFY

High resolution XANES

CeO2 XAS

Conventional TFY

High resolution

(HERFD-XAS)

Fine structure of 5d band

4f

5d

Resolve fine structure in 5d band (crystal field splitting)

Resolve 4f orbitals

High resolution XANES

2p3d (La) RIXS plane in CeO2

2p3/2 hole

3d

ho

le

• The 3d and 2p core hole potentials are similar.

• Weak interaction of core hole with photoexcited

electron

Spectral features appear along diagonal streak.

Hämäläinen et al., Phys. Rev. Lett. 67 2850 (1991)

Carra et al. PRL 74 3700 (1995)

Glatzel et al., J. Electr. Spectr. Relat. Phenomena 188 (2013) 17-25

Kotani et al., J. Electr. Spectr. Relat. Phenomena 184 (2011) 210–215

z3d

Direct study of the valence shell

Ce 2p → 4f excitations

Kvashnina et al., JAAS 26 1265 (2011)

p

p

2

2

d

d

3

3

Ground State

Intermediate (absorption) State

Final State

Tota

l E

nerg

y

Energy

transfer

Incident Energy

XAS

Emitted Energy

XES

Lifetime broadening and continuum excitations

The RIXS planeTota

l E

nerg

y

Incident Energy

Energ

y T

ransfe

r

Energy

transfer

The RIXS/RXES plane

Incident Energy

Energ

y T

ransfe

r n

fEnerg

y T

ransfe

r

n

f

f

outingf

n ningnin

outoutin

KH EEiEE

gOnnOfF

2† ˆˆ

),(

Simplifying the Kramers-Heisenberg Formula

Ignore Interference and simplify:

f

outingf

n ningnin

outoutin

KH EEEE

gOnnOfF

22

22†

)(

ˆˆ

),(

|g>, Eg

|n>, En

|f>, Ef

in

Interference changes intensities but not energies.

out

Does the scattered photon forget?

f

outingf

n ningnin

outoutin

KH EEiEE

gOnnOfF

2† ˆˆ

),(

Simplifying the Kramers-Heisenberg Formula

Ignore Interference and simplify:

|g>, Eg

|n>, En

|f>, Ef

Interference changes intensities but not energies.

XASXES

f

outingf

n ningnin

outoutin

KH EEEE

gOnnOfF

22

22†

)(

ˆˆ

),(

Tota

l E

nerg

y

Tota

l E

nerg

y

Atomic multiplet model calculations for 4f0

2p54f1 2p54f1

3d94f13d94f1

No 3d – 4f interaction With 3d – 4f interaction

4f0 4f0

4f0

No 3d – 4f interaction With 3d – 4f interaction

Tota

l E

nerg

y

Tota

l E

nerg

y

2p54f2 2p54f2

3d94f23d94f2

4f1 4f1

Atomic multiplet model calculations for 4f1

4f1

Kvashnina et al., JAAS 26 1265 (2011)

No 3d – 4f interaction With 3d – 4f interaction

Tota

l E

nerg

y

Tota

l E

nerg

y

2p54f2 2p54f2

3d94f23d94f2

4f1 4f1

Atomic multiplet model calculations for 4f1

4f1

Kvashnina et al., JAAS 26 1265 (2011)

Interference No Interference

Comparison with Experiment

4f0 4f1

Interference No Interference

Experiment

Theory

Kvashnina et al., JAAS 261265 (2011)

A little history of Ceria

The Relevance of Ceria

The Spectroscopy on Ceria

The Theory applied to Ceria

The Confusion around Ceria

The Defects in Ceria

The Relevance of CeO2

Solid oxide fuel cell

PNAS 2006;103:3495-3496

CeO2 ↔ CeO2- + /2 O2

Labeling of cancerous cells

Have we understood bulk CeO2?

Atomic Structure of Ceria

CeO2

Formally: CeIV 4f0

Cubic

One Ce site

Bulk Ceria during the 80’s

Ce 4f and O 2p mix

4f levels are populated in ground state

n4f ~ 0.5

1983

Homogeneous mixed valence

4f0

Bulk Ceria during the 80’s

3d XPS

Fujimori, PRB 28 2281 (1983)

Homogeneous mixed

valence

Bianconi et al., PRB 35 806 (1987)

4f0

2p3/2 XAS

Bulk Ceria during the 80’s

Wuilloud et al. PRL 53 202

(1984)

« a mixed valence can be

definitely excluded »

Nakano et al. JPSJ 56 2201

(1987)

« The number of 4f electrons is

between 0.36 and 0.54 «

Homogeneous mixed

valence

4f0

4f0

Bulk Ceria in the 21st century

4f0

4f0

RIXS:

Sham et al. Phys Rev B 72, 035113 (2005):

“… CeO2 in the initial state is Ce4+ (4f0) ...”

Hybrid DFT:

Graciani et al. J. Chem. Theory and Comp. 7 56 (2011)

“All valence Ce states, including the 4f states, are empty”

Almost all publications presenting DFT calculations

Bond Valence Method:

Shoko et al. Phys Rev B 79, 134108 (2009):

“… we conclude that CeO2 is a mixed-valent

compound....”

RIXS:

Kvashnina, Kotani, Butorin, Glatzel

J. Electr. Spectr. Relat. Phenomena 184 (2011) 210–215

Sadly, very little new insight over the past 30 years.

Can we determine the charge per atom?

Cococcioni et al. (PRB 71 035105 (2005)) :

“… there is no unique or rigorous way to define occupation of localized atomic levels

in a multiatom system…”

Ce d-DOS

Ce f-DOS

O p-DOS

Metal ionLigand

e-

+ + e-

photoexcitation

Metal ionLigand

Ground State Excited State

e

a

e

b

screened

Non-screened

The Single Impurity Anderson Model

4sin4cos 10 Lffg

b bb

Gunnarsson and Schönhammer, PRB 28 4315 (1983)

e-

Multi-electron excitations in CeO2

~f0

~f1L Total fluorescence yield

High resolution XAS

One-electron calculations

Surface reduction observed using TEM-EELS

Turner et al.,

Nanoscale 3 3385

(2011)

CeO2 on Pt (111) under vacuum

with L. Amidani, F. Pagliuca, F. Boscherini

In-situ study of CeO2 nanoparticle synthesis

10 mM

ACS Nano, 2013, 7 (12), pp 10726–10732

IN-SITU STUDY OF CEO2 NANOPARTICLE SYNTHESIS

5710 5720 5730 5740 5750 5760 5770 5780

5716 5718 5720 5722

Inte

nsity/a

.u

Energy /eV

Inte

nsity/a

.u

Energy /eV

Reaction time/hr

Ce(NO3)3.6H2O

CeO2

Pre-edge

2p → 4f

0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

Ce4+

Ce3+

We

ight

fra

nctio

nReaction time/h

Ce(NO3)3

CeO2 NP

60 seconds one scan

ACS Nano, 2013, 7 (12), pp 10726–10732

BLURRING OF 5D BAND STRUCTURE

5.72 5.73 5.74 5.75 5.76

NPs 25 nm

NPs belt

NPs 15 nm

NPs 10 nm

NPs 3.2 nm

No

rma

lize

d in

ten

sity (

a.u

.)

Incident energy (keV)

5d band

3 nm

Paun et al., J. Phys. Chem. C 2012,

116, 7312-7317

Ce ion Ligand

e-

SPIN MULTIPLICITY AND ORBITAL MOMENT

4sin4cos 10 Lffg

b bb

1S

Ce ion Ligand

e-

14 fg

b

2F2S+1L

CeO2 CeO2-

DIRECT STUDY OF THE VALENCE SHELL

1S

2F

Kvashnina et al., JAAS 26 1265 (2011)

THE CE 4F LEVEL IN NANOPARTICLES

5.718 5.720 5.722 5.724 5.726

No

rma

lize

d in

ten

sity (

a.u

.)

Ce(NO3)3

NPs 25 nm

NPs belt

NPs 15 nm

NPs 10 nm

NPs 3.2 nm

Incident energy (keV)

2F

1S

No Ce 2F in nanoparticles → Are they chemically active?

CHEMICAL ACTIVITY: ADDING H2O2

Celardo et al., Nanoscale 3 1411 (2011)

1

2

6 5

4

3

7

Balancing ROS levels

CHEMICAL ACTIVITY: ADDING H2O2

5710 5720 5730 5740 5750 5760

3nm CeO2

25nm CeO2

Inte

nsity/a

.u

Energy/eV

f1L f0

H2O2

0 5 10 15 20

0.48

0.52

0.56

0.60

f-o

ccu

pancy

Time/hrs

4f-

occupancy

3nm, 25 nm

Time/ hrs

“Reduction”0 5 10 15 20 25 30

3.0

3.5

4.0

4.5

5.0

5.5

CeO2NPs (3nm) + H

2O

2

CeO2NPs (3nm)

pH

Days

IS THERE ANY CE3+ 2F ?

Consistent with initial increase of electron density on Ce and subsequent “oxidation”

No observation of Ce3+ 2F

5716 5718 5720 5722

3nm CeO2

25nm CeO2

Inte

nsity/a

.u

Energy/eV

2p – 4f

0 5 10 15 20

0.48

0.52

0.56

0.60

f-occup

ancy

Time/hrs

4f-

occupancy

3nm, 25 nm

Time/ hrs

ACS Nano, 2013, 7 (12), pp 10726–10732

Electron Sponge

Core-to-core RIXS

Ground State

Intermediate (absorption) State

Final State

Tota

l E

nerg

y

Energy transfer

Incident Energy

XAS

Emitted Energy

XES

~900 eV

Core-to-valence RIXS

Ground State

Intermediate (absorption) State

Final State

Tota

l E

nerg

y

Incident Energy

XAS

Emitted Energy

XES

~1 eV

No core hole in the

final state !

Photon-in/photon-out spectroscopic techniques

1s

2p

3p

L, (3d)

3dEF

vtcKb rvtcrKb

Non-resonant Resonant

TS-1

Titanium in Silicalite – TS-1

NH3

DFT calculations

NH3

Exp. Theory

1 2

ChemPhysChem 14, 79-83 (2013)

DFT and vtc XES

E. Gallo and P. Glatzel, Advanced Materials (2014)

VBs MOrMO

1

Ti silicalite

Use Kohn-Sham orbitals:

Application of RIXS: Combine with magnetic circular dichroism

3d TM X-ray Magnetic Circular Dichroism

L-edge MCD is a great success because of sum rules to determine spin and

orbital angular moments.

In situ experiments at the L-edge very challenging or impossible.

Hard X-rays at the K-edge probe the p-DOS → very weak MCD effect

K-edge MCD difficult to interpret (no spin-orbit split edge)

Compatible with in situ experiments

Magnetic circular dichroism

Energy

g

n

B

B

1Dm 1Dm

XMCD arises from removing the

degeneracy with respect to the magnetic

quantum number m by more than kT and

macroscopically orienting the moments.

Different final states are reached

following the selection rules.

Derive sum rules using ligand field

multiplet theory.

The RIXS-MCD Energy Scheme

Magnetite (Fe3+)tetra (Fe3+)octa (Fe2+)octa O4

RIXS-MCD Experimental Setup

The first RIXS-MCD plane

Experiment Theory

M. Sikora, A. Juhin, et al. PRL 105, 037202 (2010)

Constant emission energy scans

CEE

Sharpening of spectral features

(decreased lifetime broadening)

XMCD enhanced by factor of ~10-20

Direct evidence for the existence of an intermediate interdiffusedlayer

APPLICATION OF RIXS-MCD

A. Juhin, A. Lopez Ortega, M. Sikora, …, J. Nogues, under review

Mn MCD signal!

Kb X-RAY EMISSION SPECTROSCOPY (XES)

x 8

x 500

Kb

The K fluorescence lines in 3d transition metals

1s

2p

3p

VS

The exchange interaction

3p

VS

Acts only between

electrons with parallel

spins and lowers the

total Energy

Etotal

Fluorescence

Exchange energy lowers total

energy

For 3d transition metals the strong chemical sensitivity of core levels does

NOT arise from screening!

Mn4+

Mn3+

Chemically sensitive !!

Chemical sensitivity of Kb Emission

Kb1,3

Kb’

MnF2: S=5/2

MnF3: S=2

MnF4: S=3/2

Wang et al. Phys. Rev. B 56, 4553 (1997)

Screening effect very small (unlike Sulfur!!).

(3p,3d) interactions are dominating.

Model systems and multiplet theory

LS

HS

Crystal field

multiplet model

Experiment

Fe2O3 S=5/2

K3Fe(CN)6 S=1/2

K4Fe(CN)6 S=0

Mn-Mg pairs in GaN

Th. Devillers, M. Rovezzi, et al. Scientific Reports 2 722 (2012)

Kb

Th. Devillers, M. Rovezzi, et al. Scientific Reports 2 722 (2012)

Mn-Mg pairs in GaN

(Mn3+)

(Mn4+)

XAS and XES in a layered Mn perovskite

x XANES

The La1-xSr1+xMnO4 series: doping dependence in powders

Kb

Emission Energy [eV]Absorption Energy [eV]

Replace La3+ by Sr2+ Formally: Mn3+ → Mn3.5+

Linear Dichroism in XES

Single crystal

monochromator

Ei, I0

SampleEi, I1

Ee, I2

e

Single crystal

monochromator

Ei, I0

SampleEi, I1

Ee, I2

e

VALENCE-TO-CORE X-RAY EMISSION SPECTROSCOPY (VTC XES)

x 8

Valence-to-Core X-Ray Emission in 3d Transition Metals

x 500

1s

2p

3p

VS

XES and XAS: Complementary Techniques

Occupied

states

Unoccupied

states

Fermi Energy

XES

XAS

Mn(V)N

1s

2p

3p

VSEF

Fine structure of valence-to-core emission lines

M

M

Transitions from:

Ligand 2p

Ligand 2s

ungerade symmetry with

respect to metal centerBergmann et al., Chem. Phys. Lett. 302 119 (1999)

Safonov et al., J. Phys. Chem. B 110 23192 (2006)

Mainly sensitive to orbitals that are centered on ligands.

Degree of ligand protonation

Lassalle-Kaiser et al., Inorg. Chem. 2013, 52, 12915−12922

ID26