Cheiron School, SPring-8, Japan
October 2, 2008

Studies on atoms and molecules
using synchrotron radiation
Kiyoshi Ueda
Institute of multidisciplinary research for advanced materials
Tohoku University, Sendai 980-8577, Japan

Introduction of myself

Prof. Kiyoshi Uedaat
Tohoku University （Sendai）
Institute of multidisciplinary research
for advanced materials
Leadinggroup for analysis of quantum
processes

Atomic and molecular science using
Synchrotron Radiation
Ueda, JPB 36, R1 (2003);
Ueda & Eland, JPB 38, S839 (2005);
Ueda, JPSJ 75, 032001 (2006);
Kabachnik et al. PR 451, 155 (2007).
Application of the SR-based
experimental techniques to laser
experiments(femtosecond laser and FEL)

Outline
1. Introduction to quantum world
2. Atomic resonant photoemission spectroscopy- Introduction to the quantum interference
3. Vibrationally-resolved core-level photoelectron spectroscopy- Franck-Condon analysis and shape resonance effects- Young’s double-slit experiments- Intermission 4. Multiple-ion momentum imaging- Snapshots of molecular deformation within a few fs
5. Electron-ion momentum imaging- Molecular frame photoelectron angular distributions- Interatomic Coulombic decay
6. Toward future- FEL experiment

Photoelectric effect
When matter is shined by the light, electron isemitted from the surface.
(i) Frequency of the light needs to be larger than ν0.
(ii) Kinetic energy of the electron is determined by thefrequency of the light.
(iii) Number of electron is proportional to the intensityof the light.

Einstein’s explanation
Light at frequency of ν is considered to be a group ofparticles (photons) and each photon has energy hν.
An electron gets the energy hν when it absorb one
photon.
The electron in the matter is bound. For the electron
to be emitted from the matter, the electron needs toreceive the energy more than the work function W.
Then the kinetic energy KE of the emitted electron canbe given as KE = hν – W.
Einstein’s miraculous year 1905, Nobel prize in 1912

Photoelectron spectroscopy (UPS, XPS)
Precision measurements for kinetic energies of photoelectrons
emitted via Einstein’s photoelectric effects

Kinetic
energyEK=hv-EB

Photoelectron
spectrum

Vacuum level
Intensity
Valence level

BindingenergyBalmer and Rydberg formulae

Balmer found beautiful regularity in the H spectrum!

ν

1 ⎞
⎛ 1
= = R⎜ 2 − 2 ⎟Rydberg formula：
c λ
n' ⎠
⎝n
1

c, speed of light; λ, wavelength; R, Rydberg constant (R =109737.309 cm-1)

Bohr’s atomic model
Electron orbits exist only when the classical orbits satisfy thefollowing condition of quantization:
2π∫ pϕ dϕ = nh
0ϕ, angle of rotation; pϕ= mer2dϕ/dt , angular momentum; r, radius; me, electron mass

The electron binding energies are discrete:
Ēn= -hcR/n2
Proposed in 1913, Nobel prize in 1922

Schrödinger equation (of H atom in atomic units)H Ψ = EΨ
H = T + U (r ) Hamiltonian22p
1 ∂ kinetic energy operator
T=
=−
2
2
2 ∂r
∂
momentum operator
p=i∂r

Proposed in 1926,
Nobel prize in 19331potential energy for H atom
U (r) = −r
1
En = − 2 eigen energy of the H atom
2n

In quantum world, wave function Ψ – which is in general acomplex number with a phase! – defines the system!

Atomic and molecular science now
Target: single atom or molecule; size: ~ 1 Å (= 0.1 nm = 10-10 m)

How to use synchrotron radiation to study atoms and molecules
We use monochromatic synchrotron radiation to excite atoms
and molecules and to study their electronic structures as wellas electron and nuclear dynamics in the excited states.
A single photon should be absorbed by a single atom ormolecule in the first step!

What photon energies to be used
Electron binding energies (eV)

Vacuum ultraviolet region

The experiments need
to be in the vacuum!
SR

Ion
detector

Mol. Beam

The easiest experiment:
ion yield spectroscopySPring-8 BL27SU
Figure-8 undulator
Linearly polarized light
Horizontal polarization (1st)Vertical polarization (0.5th)
T. Tanaka and H. Kitamura, J. Synchrotron Radiation 3, 47 (1996).

Soft X-ray monochromator
Hettrick type: varied line spacing plane grating
Energy range

0.15 ~ 2.5 keV

Photon Flux

> 1011 photon/s

Energy resolution

10000 - 20000

H. Ohashi, Y. Tamenori, E. Ishiguro et al. Nucl. Instr. Methods A 467, 533 (2001).

Ne 1s total ion yield spectrum
np Rydberg series- Ēn = IP – En = R/(n-μ)2

μ: quantum defect, R =13.6 eV

IP

Σ

σn
σ = σdir++ σ1s ε = (hν-En)/(Γn/2)21+εnn
σn ∝ 1 /(n − µ )3
Γn= const!

Auger decay and Auger electron spectroscopy
Photoelectron or
Rydberg electronCore hole lifetime
defines the line width!

Auger electron

SES2002 analyzer•

Electrostatic hemisphericalanalyzer– Mean radius 200 mm– ∆E/PE=1/1600(66 meV at pass 100 eV)– MCP+CCD cameraor MCP+Delay line anode– Gas cell system
or Doppler-free molecular beamsourceUeda et al. PRL . 90, 153005(2003)
or effusive beam + momentum
resolved ion spectrometer
Prümper et al. PRA 71, 052704,(2005).

Angle-resolved resonant Auger spectra of Ne at
1s -> 3p excitation

2p-2(1D2)3p

P2 (cos θ ) = [3 cos2 θ − 1] / 2
β: asymmetry parameter
Measured angular distributions tell us how theangular momenta are coupled in the atom ,allowing us the spectroscopic assignment !
Shimizu et al. J. Phys. B 33, L685 (2000).

Resonant Auger spectra of Ne “between”
1s -> 3p and 1s -> 4p excitations⎛ β⎞
I (0) ∝ σ (1 + β ) I (90) ∝ σ ⎜1 − ⎟⎝ 2⎠σ ∝ I (0) + 2 × I (90)2p-2(1D2)3p

Interference effects among difference paths
DnαΑα = d α +i+εnnσα = |Αα |2Σεn = (hν-En)/(Γn/2)
dα = <g|r|α>Dnα = <g|r|in><in|α>
|i>

|α>

Dnα
dα
|g>

De Fanis et al. Phys. Rev. Lett. 89, 023006 (2002).

Sendai City

Statue of Load Date

Jozenji Street

Introduction of molecular worldHΨ( R, r ) = EΨ( R, r )∂2hTR = − ∑2 k Mk ∂Rk2

KE of nucleus

H = TR + Tr + V (r, R)h∂2
Tr = −∑
2m j ∂rj2

KE of electrons

H 0 = Tr + V (r , R)

H = H 0 + TR

[ H 0 − ε n ( R )]ϕ ( R, r ) = 0
ε n (R ) : adiabatic potential energyΨ ( R, r ) = ∑ Φ n ( R)ϕ n ( R, r )n∫ ϕ ( R, r)( H − E )Ψ( R, r)dr = 0*

0[TR + ε m ( R)]Φ 0mv ( R) = Emv
Φ 0mv ( R)

Nuclear motion is within the adiabatic potential energy surface!

Born-Oppenheimer approximation

Franck-Condon approximation for photoionization

σ iv+' (E) ~| ∫ X iv* ' (R)DE (R) X 0 (R)dR |2

Xiv* ' ( R), X 0 ( R) : Vibrational wavefunctions of ionic iv’ and ground 0 states

D E ( R ) = ∫ ϕ E* ( r , R ) r ϕ core ( r , R ) d r

ϕ E ( r , R ), ϕ core ( r , R ) : Electronic wavefunctions of the continuum E and core orbitals
Assume that the dipole moment DE(R) does not depend on R

σ iv+' ( E) ~| DE (Re ) |2 F (v'0)
F ( v '0 ) = | ∫ X iv* ' ( R ) X 0 ( R ) d R |2 Franck-Condon factor
Vibrational intensity distribution in the photoelectron
spectrum is determined by the Franck-Condon factors

Franck-Condon analysis based on harmonic approximation- Linear coupling model Intensityν‘ = 2

F (1,0) =Ionic stateν‘ = 1α ( ∆R ) 2
2⎛ α ( ∆R ) 2 ⎞⎟⎟exp⎜⎜ −2 ⎠⎝α = µω hν‘ = 0∆R

Photoelectron
spectrumν=0Electronic
ground state

R0

R'0

⎛ α ( ∆R ) 2 ⎞⎟⎟F (0,0) = exp⎜⎜ −2 ⎠⎝F(1,0) α(∆R)=
2F(0,0)

2

Internuclear distanceOne can extract ∆R from photoelectron spectroscopy!

Franck-Condon analysis for the vibrational structureof the C 1s and O 1s mainlines of COΙ ∼|<ψ+v|ψ0>|2 : FC factor
ψ0: v=0 vibrational wave functionin the ground stateψ + v: v-th vibrational wave functionin the core-ionized state
Stable geometry of the core-ionized state
extracted from the vibrational structure
Exper.

TheoryC 1s-1∆Re (Å) -0.051 (1)-0.051O 1s-1∆Re (Å) 0.037(2)0.028Matsumoto et al. Chem. Phys. Lett. 417, 89-93 (2006).

Satellite spectrum in core-level photoemission in CO

HOMO-LUMO

π−π∗Mainline

Ehara et al. J. Chem. Phys. 125, 114304 (2006).

Franck-Condon analysis of the vibrational structure in
the symmetry-resolved C 1s satellite bands of CO

Solid lines: measured
symmetry resolved
spectraVertical bars: ab initio
FC factors

Ab initio potential curves

Ab initio FC factors reproduce themeasured vibrational distributions.
Ueda et al., Phys. Rev. Lett. 94, 243004 (2005).

Vibrational effects on the shape resonance energy in the K-shell
photoionization spectra of CO

Shape resonancehν=551.5 eV

10Intensity (arb. units)

Intensity (arb. units)

10
8
6
4
2
0

Shape resonance:
Promotion of a core electron to a σ*antibonding orbital
Temporal trapping of a photoelectron by
the molecular potential

8
6
4
2
0

7.0

7.5
8.0
Kinetic energy (eV)8.5hν=559.0 eV

14.5

15.0
15.5
Kinetic energy (eV)16.0

O 1s photoelectron spectra of CO at the shape resonance and far above it.
Non-Franck-Condon behavior of vibrational distributions!

10

DE (R)

O 1s

Cross sections (arb. units)

Cross sections (arb. units)

Vibration-dependent shape resonances
v=0

v=1 (x 2)

5
v=2 (x 5)

0

4

6

8

10

12

14

16

18

Kinetic energy (eV)

10

v=0

C 1s

v=1

5
v=2

0

4

6

8

10

12

14

16

18

Kinetic energy (eV)

Shape resonance energy increases with v’. Shape resonance energy decreases with v’.
D. A. Mistrov et al. Phys. Rev. A 68,
022508 (2003).

K. J. Randall et al., Phys. Rev. Lett. 71,
1156 (1993).

σ iv+' (E) ~| ∫ X iv* ' (R)DE (R) X 0 (R)dR |2 , DE ( R ) = ∫ ϕ E* (r , R )rϕcore (r , R )dr
DE（R) strongly depends on R in the shape resonance region!
J. L. Dehmer, D. Dill, and S. Wallace, Phys. Rev. Lett. 43, 1005 (1979).

Origin of the vibrational energy on the shaperesonance energy
e
C1s

Re

Characteristic bond length
shrinks with the increase
in v’ for O 1s.
Characteristic bond length
elongates with the increase
in v’ for C1s.

O1s

C

O

O 1s-1
v’=2
v’=1
v’=0

C 1s-1

v’=2
v’=1
v’=0

Shape resonance formation:RekR + ϕ = πRe

Cf. standing wave in the box potential (ϕ=0)
D. A. Mistrov et al.
Phys. Rev. A 68, 022508 (2003).

1.0

1.1
R (Å)

1.2

1.3

e

N(1)

Evidence of the dualityof waves and particles!

N(2)Electrons also showinterference fringes!

Evidence that the light is the wave!

Franck-Condon analysis for the vibrational structureof the N 1s 1σu and 1σg mainlines of N2
2500

1500
1000
500
0

90.0

90.5

91.0

Kinetic energy (eV)

(1σu)
-1
(1σg)
-1

Relative intensity

Counts2000

N2 N 1shν=500 eV

SAC-CI
v’=0

Exper.

v’=1
90.0

90.5

Equilibrium geometries of the core-ionizedstates extracted from the vibrational structure

91.0

Kinetic energy (eV)N 1σu-1∆Re (Å) -0.023(1)N 1σg-1∆Re (Å) -0.018(1)Theory-0.021-0.017

Ehara et al. JCP 124, 124311 (2006)

Cohen-Fano two-center interference
Two 1s ortibals in N2 correspond to Young’s double slits.
Molecular core-level ortibals:
Core-level photoemission from fixed-in-space N2:

Two center photoelectron wave

Interference fringe

where k: photoelectron momentum; R1,R2: position vectors of N (1) and N(2)Orientational average: Cohen-Fano formulaInterference oscillatory structure becomes much smaller but remains!
H.D. Cohen and U. Fano, Phys. Rev. 150, 30 (1966).

Ab initio N 1s 1σu and 1σg photoionization cross sections of N2

Oscillation:
Two-center Interference
Cohen-Fano prediction !

Semenov et al., J. Phys. B: At. Mol. Opt. Phys. 39, L261 (2006)

σg /σu ratio: experiment vs ab initio and Cohen-Fano
2.2

N2 K shell/
Experiment
Original Cohen-Fano
RPA

Cross section ratio σg/σu

2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
1

2

3

4

5

6

Electron momentum (a.u.)
Both experimental and ab initio interference fringes shift from the prediction
by Cohen-Fano formula!
Liu et al., J. Phys. B. 39, 4801-4817 (2006); JESRP 156-158, 73-77 (2007).

Photoelectron scattering by the neighboring N atom
The amplitude of the photoelectron wave from one center:ψ2 = Α2+Β2

A1

B1

The amplitude of the photoelectron wave from two centers: ψ1 ± ψ2

Cohen-Fano interference
A1A2 interference term
N(1)

N(2)

N(1)

N(2)

The cross section~ |ψ1 ± ψ2 |2 = |(Α1+Β1) ±(Α2+Β2) |2

0

A1B1 and A2B2 one-center interference terms

δ1(k): scattering phase
CF A1A2 interference term

A1B2 and A2B1 two-center interference terms !

σg /σu ratio fitted by modified Choen-Fano
2.2

N2 K shell/
Experiment
Original Cohen-Fano
Modified Cohen-Fano

Cross section ratio σg/σu

2.0
1.8
1.6

Scattering phase: 2δ1(k)= a + bk + ck2

1.4

Cohen-Fano: a=b=c=0

1.2
1.0
0.8
0.6
1

2

3

4

5

6

Electron momentum (a.u.)
Fitted results: a = −5.2±0.6, b = −1.6±0.4, c = 0.09 ± 0.05 a.u.
Ab initio results: a = −4.8, b = −1.15, c = 0.069 a.u.
(Teo and Lee, J. Am. Chem. Soc. 101, 2815 (1979))

Intermission

Motsu-ji

Near Sendai
Matsushima
Matsushimabay

Mt. ZaoZao
Mount

Chuson-ji

Multiple-ion coincidence imaging setup
E field

Y Ion 2D

field free
TOF tubehν electron
MCP

PSD
x2y2t2
x1y1t1t0

t, Z 80mm

x4y4t4X
x3y3t3supersonic jet

25

70

140 mmskimmer
Sample gas jet
position & time of flight (x,y,t)

3D momentum of each particle

How to obtain 3D momentum

t: ion time-of-flight6

to: ion TOF at rest

TOF of 2nd ion (µs)
24m (x − x0 )m ( y − y0 ), py =, p z = qE (t − t0 )
px =
t
t

x, y: arrival position on the detector.
x0, y0 : initial position of the ion
m : ion mass
q: ion charge

O+ + CO+C+ + O +E: electric field in the acceleration region
2

4

TOF of 1st ion (µs)

To be exact Pz becomes nonlinear

Iterative procedure6

Total ion yield spectrum of CO2 in the C1s ionization region
CO2 ground state configuration:
1σg21σu22σg23σg22σu24σg2
O1s

C1s

O2s

C2s

3σu21πu41πg4(1Σg+); 2πu05σg04σu0

Intensity (arb. units)

π2
*π

σ

u ← 2 g resonance

TIY

297.63 eV
C K-edgeresonance
4σu ← σ2u σshapeg shape resonance-2e exc.

290

295

300

305

310

315

Photon energy (eV)

320

325

SR experiments with multiple-ion coincidence
E fieldhν

Y Ion 2D

field free
TOF tube

electron
MCP

PSD
x2y2t2
x1y1t1t0

t, Z 80mm

X
x3y3t3supersonic jet

25

70

140 mmskimmer
Sample gas jet
CO2
position & time of flight (x,y,t)

CO23+ -> C+ + O+ + O+
3D momentum of each ion

O

Renner-Teller splitting of CO2

C

Out-of-plane 2πu: B1
CO2

C1s-1 2πEuO
Bending plane ⊥ E

In-plane 2πu : A1

OO

CO2 Ground stateFranck-Condon
region180ºBond angle

E

C
Bending plane // E

Snapshot of the bending motion in the core-exited statewith a liftetime ~7 fs
Newton DiagramOut-of-plane 2πu: B1
LinearIn-plane 2πu : A1
Bent

Muramatsu et al. Phys. Rev. Lett. 88, 133002 (2002).

BF3

KK (1a1’)2(1e’)4(2a1’)2(2e’)4(1a2”)2(3e’)4(1e”)4(1a2’)2 ; (2a2”)0(4e’)0

inner valenceD3h planar

F, B 1sempty

outer valence

Asymmetricstretching?

F 1s excitation/ionization
Symmetry breaking (due to vibronic coupling)3

4e'(σ )

Intensity (arbitrary units)

Intensity (arbitrary units)

2a2 "(π )

2

1

0
685

690
695
700
Photon energy (eV)705

F1s excitation spectrum

0
15

16
17
Kinetic energy (eV)18

F1s photoelectron spectrum

Multiple ion coincidence momentum imaging
E fieldhν

Y Ion 2D

field free
TOF tube

electron
MCP

PSD
+

F

F+

x2y2t2x4y4t4et0t, Z 80mm

B+
x1y1t1F+

supersonic jet

25

X

x3y3t370skimmer

140 mm

F 1s ionization: BF3+
Sample gas jet
Triple Auger decay: BF34+
BF3
Coulomb explosion: B++F++F++ F+

Construction of Dalitz plots for F+ F+ F+
in the plane perpendicular to P(B+)
1
YD=εF 0.6+

1P
⊥F+i are the projectionsof momenta on theplane perpendicular to
the emission of B+

3

0.3

εF

+

0.0

εF

2

+

εF

+

3

1

-0.3

2

P
εF+i = ⊥F2+i
ΣP⊥F+i-0.3

ε F −ε F
0.0

XD=

+

3

31/2

+

0.3

2

Motion of F+ F+ F+ in the plane perpendicular to P(B+)
B1s ionization⇓

F+ have similar
momenta P⊥

symmetric stretchingF1s ionization
asymmetricsharing of
momenta P⊥⇓

D3hasymmetric stretching ?
C2v

Newton diagrams for symmetric and asymmetric nuclear
motion probed by quadruple ion momentum imaging

B

1

(I)

Edge

p(B+)

p(Fc+)0-1-2

Fp(Fa+)-1

0

1

Relative momentum

Relative momentum

Center
1

(II)

p(B+)

p(Fb+)0p(Fc+)-1p(Fa+)-2-1

0

1

Relative momentum

Relative momentum

symmetric

asymmetric

Asymmetric nuclear motion as result of symmetry breaking by
F 1s ionization can be detected only via quadruple ion
momentum imaging.
De Fanis et al. Phys. Rev. A 69, 022506 (2004).

Sendaiin summer

Tanabata festivalElectron-ion coincidence momentum imaging
Multihit 2D detector

Multihit 2D detector
Electric field

Y

Y

N+
B
e-

B+
e- N
O+
A

O+
A

X

X
X-raysMagnetic field

Ion-ion coincidence

Molecular axis

Ion momentum conservation

Retrieval of the source point

Electron-ion-ion coincidence

Molecular-frame e- angular distribution

Towards photoelectron diffraction measurement

Electron yield spectrum of CO2 in the C1s ionization region
4σu ← 2σg shape resonance
CO2 ground state configuration:
1σg21σu22σg23σg22σu24σg2
O1s

C1s

O2s

C2s

3σu21πu41πg4(1Σg+); 2πu05σg04σu0
C 1s threshold
297.63 eV

N. Saito et al., J. Phys. B, 36 L25 (2003).

Reaction plane
Reaction plane ＝plane define by the E vector and molecular axis

eElectron emission
direction
OθElectric vector

θnCO
Molecular axis

We focus on the electron emission within this reaction plane

MFPADs for C1s emission from CO2:
comparison between experiment and theory
Photon energy

Shaperesonance

The general agreement between experiment and theory is reasonable.
Liu et al. Phys. Rev. Lett. 101,083001(2008).

Satellite line vs Main line
Y axis： θehν = 312.2 eV

8000

countse-

X axis： θnPhotoelectron spectrum

6000
4000
2000
0
0

5

10

15

20

electron kinetic energy

Satellite

Mainline

180

θe

180

135

135

90

θ e 90Emission
perpendicular to
the molecular axis

45
0
0

45

θ n90

135

Emission along
the molecular axis

45
0
180

0

45

θ n90

135

180

In both cases, the intensity drop at θn =90° i.e. Σ−Σ parallel transition.
The electron emission directions are completely different.
Liu et al. Phys. Rev. Lett. 101, 023001 (2008).

Auger vs Interatomic Coulombic Decay (ICD)

Ne

Intra-atomic

high-energy Auger e-

Energy transfer via
virtual photon exchange

low-energy ICD e-

ICD rate is R dependent!

Interatomic Coulombic Decay (ICD)
TheoreticalFirst prediction - HF cluster:
L.S. Cederbaum, J. Zobeley, and F. Tarantelli, Phys. Rev. Lett. 79, 4778 (1997).
Prediction - Ne dimer:
R. Santra, J. Zobeley, L.S. Cederbaum et al., Phys. Rev. Lett. 85, 4490 (2000).
Prediction - ICD from Auger final states in Ne dimer:
R. Santra and L.S. Cederbaum, Phys. Rev. Lett. 90, 153401 (2003).

Experimental
First observation - Ne cluster:U. Hergenhahn and coworkers, Phys.Rev. Lett. 90, 203401 (2003).
Cluster-size-dependent lifetime:
G. Öhrwall et al., Phys. Rev. Lett. 93, 173401 (2004).
Ne2 e-ion-ion coincidence:
R. Dörner and coworkers, Phys. Rev. Lett. 93, 163401 (2004).

Observation of ICD in Ne2 by Frankfurt group
Ne2+ (2p-2)
Ne+ (2s-1)

5.16 eVICD Ne+(2p-1) + Ne+(2p-1)

40

+

-1

Ne (2p )20

Potential energy

エネルギーレベル (eV)

60

AB+

(a) (b)KE(e)KER
A+ + B +0R
KE(e)+KER = 5.16 eV

Ne+

Ne+

Electron-ion-ion coincidence momentum imaging

T. Jahnke et al.
Phys. Rev. Lett.
93, 163401 (2004)

Experimental evidence of interatomic Coulombic
decay from the Auger final states in argon dimers(a) Core photoionization and Auger decay

2p ionization

Auger(b) Interatomic Coulombic decay
ICD electron
virtual photon

SPring-8 view from sky

ICDMorishita et al. Phys. Rev. Lett. 96, 243402 (2006).

(c) Fragmentation

Ar2+

Ar+
fragmentation
We detect ICD electrons in coincidence with Ar+ and Ar2+
using e-i-i coincidence momentum spectroscopy

Multiple coincidence momentum imaging
Multihit 2D detector

Multihit 2D detector
Electric field

Y

Y

N+
B
e-

B+
e- N
O+
A

O+
A

X

X
X-raysMagnetic fieldposition & time of flight (x,y,t)Multiple coincidence
Momentum conservation

3D momentum of each particle
Momentum correlation
among the particles
Selection of Dimer from others !

TOF of Second Ion (µs)

Ar2

PIPICO spectrum

864
filtering
22

4
6
TOF of First Ion (µs)
Filter conditions:
Ar+/Ar+: the sum of the momentumof Ar+ and Ar+ ~ 0
Ar++/Ar+: the sum of the momentumof Ar++ and Ar+ ~ 0

Ar++/Ar+ comes from ICD !?

Electron spectrum, KER, and their correlation
Electron spectrum coincident with Ar++/Ar+

Equilibrium distance
3.8 A ++Ar+Ar
Coulomb explosion( expected KER ~ 7.6 eV)
KER
Ar++/Ar+
Measured KER~ 7.7 eV

ICD: KER + KE(ICD electron) ~ constantIslands of slope -1 are ICDs !

Breakup following ICD takes placealmost instantaneously.

ICD is very fast!

Photoelectron ejection(13.4 and 11.3 eV)

Potential energy

Energy diagram of
the ICD process in Ar2

Binding Energy (eV)80

hv=262 eVphotoionization

3s-2
3p-33d(１P)70(a) (b)
KE(e)

Ar3+

Auger decay

2p-1

AB*

R

ICD &
fragmentation

CI
3s-13p-1 (１P) 10eV

60

KER
A+ + B

3p-1 & 3p-2 (１D)

50

3p-2
40

Ar

Ar+

Ar

Ar2+

KER
+ ICD electron= 10 eVAr+

Ar2+

ICD from the Auger final states in Ne dimerNe+＋

1s photo-e

Ne

BESSY

Auger
Ne+＋

Ne＋

Kreidi et al. J. Phys. B. 41, 101002 (2008).

ICD

Ne++

Ne+
fragmentation

We detect ICD electrons in coincidence with Ne+ andNe2+using e-i-i coincidence momentum spectroscopy

ICD channels in Ne2 after KL1L23 Auger
Ee1

Ee1 + KER = 11.2 eV
1

R~R0

1

2

Ne + + (2 s −1 2 p −1 P ) - Ne − > Ne + + (2 p −1 2 p −1 D ) - Ne + ( 2 p −1 P )1s photo-e

98.5 eV − (65.7 + 21.6) eV = 11.2 eV

Ee1 + KER = 14.4 eV
1

32

Ne + + ( 2 s −1 2 p −1 P ) - Ne − > Ne + + ( 2 p −1 2 p −1 P ) - Ne + ( 2 p −1 P )KER~9.5 eV~13 eV

98.5 eV − (63.5 + 21.6) eV = 14.4 eV
1KER

Spin flip!

Ee1

ICD-e

3

Ne + + (2 s −1 2 p −1 P ) − > Ne + + ( 2 p −1 2 p −1 P )after bond shortening

Exchange !

KER + Ee1

R~2.2 A < R0 = 3.2 A

Molecular frame electron angular distributions
emitted via ICD
ICD by virtual photon exchange(direct integral)
ICD electron is emitted from Ne+ site

Ne++

Ne+

Flipped!

ICD by electron transfer(exchange integral)
ICD electron is emitted from Ne++ site

Ne++

Ne+

Wave packet dynamics on ab initio
potential energy curves

Stoychev et al. J. Chem. Phys. 129, 074307 (2008).

Electron exchange
ICD

Virtual photon exchange
ICD
Ne++(2s-1 2p-1 1P)

Ne++(2p-2 3P)+ Ne+(2p-1 2P)

Ne++(2p-2 1D)+ Ne+(2p-1 2P)

Importance of ICD
1. ICD takes place as a result of the interaction between themolecule and the environments
2. ICD takes place in any van der waals molecules and clusters,
any hydrogen-bonding clusters, any atoms in the C60 cage,
any bio-molecules in the living cell, etc.
3. ICD takes place after inner-valence ionization, after shakeup
ionization, and after Auger decay.
4. ICD is the important mechanism to produce the low-energy
electron after hard X-ray radiation and may be one of thesource of radiation damage.

Ultrafast imaging of asingle molecule using
XFEL
SCSS
2009

2010

DESY X-FEL

2012

Structure analysis for a single biomolecule
Neutze, Wouts, van der Spoel, Weckert, Hajdu Nature 406, 752 (2000)
BeforeDuring ~10 fs

After ~50 fs

Should record the X-ray diffraction pattern before Coulomb explosion….
Change of the electron density may be even faster….
Developing the X-ray detectors is the most important issue….

EUV-FEL Facility
X-FEL (will be in operation in 2010)
EUV-FEL SPring-8(in operation)

Characteristics of EUV-FEL
Energy range

51 - 61 nm (20 - 24 eV)Band width<1%

Pulse Energy> 10 µJ at 61 nm

Stability of pulse energy< 20 %

Pulse width~ 100 fs

Period of Bunch

10 Hz ( 60 Hz in future)

Polarization

Horizontal (> 99 %)Higher harmonics at 54 nm

Second < 0.1 %Third < 1 %A lot of new opportunities for atomic and molecular science!

The endThank you very much for your attention!