Strong-Field Imaging of Molecular Dynamics

Wendell T. Hill, III University of Maryland

Department of Physics and

Institute for Physical Science and Technology

Explosion EnergiesLight AtomsLight Atoms Heavy AtomsHeavy Atoms

nm 28.0∪cRnm 38.0∪cR

~40% of Eeq

~70% of Eeq

Normand, et al., PRA 53, R1958 (1996)

Cornaggia, et al., PRA 44, 4499 (1991)

R

ZZE 21

ex =

Enhanced Ionization at Rc

R = Req R = Req R > Req

I

( )( ) 2111

2111

21

21

ss

ss

u

g

−♦

+♦

σ

σFR/2

Posthumus, et al. J.Phys.28; Zuo & Bandrauk, PRA 52; Seideman , et al. PRL 75

Posthumus, et al. J.Phys.28; Zuo & Bandrauk, PRA 52; Seideman , et al. PRL 75

Enhanced Ionization: Theory

Manybody S-Matrix; J. Muth-Böhm, A. Becker and F. H. M. Faisal, ICOMP VIII (99)

Numerical Integration of SE in 3D; Zuo and Bandrauk, PRA 52, R2511 (195)

H2 Explosion Energy: Experiment

Gibson, et al., PRL 79, 2022 (1997)

Zuo and Bandrauk, PRA 52, R2511 (1995)Theory Rc=4/IP (au)

Zhang and Hill, unpublished

3-Atom Enhanced Ionization at Rc

RC 0.22 nm (4 au)

- 10 - 5 0 5 10xHauL

- 2

- 1.5

- 1

- 0.5

0I=3.55́ 1014W?cm2

Ip=1.29auZ=2 Rc=4.74au

- 10 - 5 0 5 10xHauL

- 2

- 1.5

- 1

- 0.5

0

ygrenE

H

ua

L

I=3.55́ 1014W?cm2

Ip=1.29auZ=2 Req=0.12au

( ) <

==ji ij

jiCCO r

ZZRrVEmea 66 eV

nh + CO2 Op+ + Cq+ + Or+

No intermediate molecular states observed!

No intermediate molecular states observed!p, q, r = 1,2,3

GENERIC XY2 LINEAR POTENTIAL SURFACE

Y+X+Y

XY+Y

Y+XYR1

R2

What about the electrons?

Dynamic Screening Explosion Model

Ionization and Dissociation InterlacedElectrons do not leave region immediately!

Dissociation begins @ Req but slowed by electron cloud

producing energies consistentwith dissociation from Rc.

Dissociation begins @ Req but slowed by electron cloud

producing energies consistentwith dissociation from Rc.

Brewczyk, Rzążewski and Clark PRL 78, 191 (1997)Brewczyk, Rzążewski and Clark PRL 78, 191 (1997)

Hering, Brewczyk and Cornaggia, PRL 85, 2288 (2000)

Thomas-Fermi Hydrodynamic Model

Static Screening Model

< =< =

=ji

Rrij

effj

effi

jiRrij

ji

eqCOCCO

r

ZZ

r

ZZ

( )Ceq RRZ −… 1σ

Zhao, Zhang and Hill, PRA (submitted)Zhao, Zhang and Hill, PRA (submitted)

σ−=ZZ eff

V 66 er

ZZ

jieq

ij

effj

effi ∪

<

+ + +

-

-

- -

-- C OO

3 4 5 6 7 8 9IonizationStage

25

50

75

100

125

150

noisolpxE

ygrenE

H

Ve

L

Dynamic ScreeningStatic Screening

Angular Dependence of EC

[ ] [ ])sin(2

)()(2 22

beq

b

eq

b

R

Z

R

Z

θ

θσθσε

−+

−=

)2/sin()(2)(

2 22

bbCbC R

Z

R

Z

θθθε +=

Time-Resolved Waveforms

Digital Scope AcquisitionMass-Resolved

Energies Distributions

Time-Resolved Images128 x 128 Pixels

730 Hz Digital Acquisition500,000 – 1,000,000 Frames

Mass-ResolvedEnergies & Angular Distributions

2.6 2.8 3 3.2 3.4TimeHusL0

0. 0005

0. 001

0. 0015

0. 002edutilpmA

CO2: Par al l elHSol i dLvs Per pendi cul arHDashedL

20 qVrE ∝

Momentum & Time-of-Flight Spectra

( )qmtfE ,;0 =qVrp ∝0

14(k) O+

720 – 820 ns(l) O+

770 – 870 ns(m) OH+

820 – 920 ns(n) N2+,3+ , O2+,3+

320 – 620 ns(o) All Ions

All Time

(f) N2+ , O2+

470 – 570 ns(g) O2+

520 – 620 ns(h)

570 – 670 ns(i) N+

620 – 720 ns(j) N+

670 – 770 ns

(a) H+

110 – 210 ns(b) H2

+

210 – 310 ns(c) N3+

320 – 420 ns(d) N3+ , O3+

370 – 470 ns(e) N2+

420 – 520 ns

10

Momentum Image

0

0

Momentum

Mom

entu

m

Scale: 5 – 8 amu/div

POLARIZATION

AXIS

Correlation Imaging

AVERAGE IMAGE SELECTIVE AVERAGE

POLARIZATIONAXIS

0 1

100 120 140 160 180qbH°L

40

50

60

70

EC

H

Ve

LSymmetric Coulomb Explosion

NO2

CO2

Across O-O

- 0.6 - 0.4 - 0.2 0 0.2 0.4 0.6 0.8xHnmL

- 0.6

- 0.4

- 0.2

0

0.2

0.4

0.6

0.8

y

H

mn

L1.94709́ 1014W?cm2

LeftCenterRight

Rc= 0.29091qb= 140

- 0.6 - 0.4 - 0.2 0 0.2 0.4 0.6 0.8xHnmL

- 0.6

- 0.4

- 0.2

0

0.2

0.4

0.6

0.8

y

H

mn

L1.80067́ 1014W?cm2

LeftCenterRight

Rc= 0.303091qb= 140

Through Minimum

Over-the-BarrierIonization

Over-the-BarrierIonization

( ) ( ) )2/sin(2

2 22

CbbCbC R

Z

R

ZE

θθθ+=

Fxsyyxx

ZV

i ii

i ++−+−

−= =

3

1222 )()(

- 10 - 5 0 5 10xHauL

- 2

- 1.5

- 1

- 0.5

0I=3.55́ 1014W?cm2

Ip=1.29auZ=2 Rc=4.74au

0 0.02 0.04 0.06 0.08sHnmL0.05

0.060.070.080.090.1

DRC

H

mn

L

- 0.6- 0.4- 0.2 0 0.2 0.4 0.6zHnmL- 100

- 80- 60- 40- 20

0

ygrenE

H

Ve

L

I = 1.75 1014 W/cm2, R = 0.294 nm, s = 0.03

- 0.6- 0.4- 0.2 0 0.2 0.4 0.6zHnmL- 100

- 80- 60- 40- 20

0

ygrenE

H

Ve

LI = 1.661014 , R = 0.302 nm, s = 0.0001

I = 3.291014 W/cm2, R = 0.216 nm, s = 0.082

- 0.6- 0.4- 0.2 0 0.2 0.4 0.6zHnmL- 100

- 80- 60- 40- 20

0

ygrenE

H

Ve

LLimits on Smoothing FactorLimits on Smoothing Factor

100 120 140 160 180qbH°L

0.5

0.6

0.7

0.8

0.9

s

0.2

0.24

0.28

0.32

0.36

0.4

RC

H

mn

L

Along Saddle PointsAlong Saddle Points

100 120 140 160 180qbH°L

0.5

0.6

0.7

0.8

0.9

s

0.2

0.24

0.28

0.32

0.36

0.4

RC

H

mn

L

Across O-O BondAcross O-O Bond

Enhanced

Ionizationat Rc

100 120 140 160 180qbH°L

0.5

0.55

0.6

0.65

0.7

0.75

s

H

e

L

0.2

0.22

0.24

0.26

0.28

0.3

RC

H

mn

LSymmetric Explosion vs. Bond Angle

( )

( )( )

= +−+−−

+=

+=

3

1222

2

2

)(

,

)2/sin(2

12

)2/sin(2

12

i Area ii

eli

beqeq

beqeqbeff

syyxx

dxdyyxqZ

RRZ

RRZV

ρ

πθ

θθ

NO2

CO2

20

2

20

2

y

y

x

x

e−−

=

Charge Density Parameters

NO2 CO2

e- e-

e- e-

ResultingCharge

DistributionWider Distribution

Larger y0

- 0.2 - 0.1 0 0.1 0.2xHnmL- 0.2

- 0.1

0

0.1

0.2

y

H

mn

L1%10%50%

- 3 - 2 - 1 0 1 2 3xHnmL- 0.1

- 0.05

0

0.05

0.1

y

H

mn

L1%10%50%

NO2 explosion rangeθb = 125 - 170°

CO2 explosion rangeθb = 145 - 180°

Linear vs. Bent Explosions

100 120 140 160 180qbH°L

0.5

0.55

0.6

0.65

0.7

0.75

s

H

e

L

0.2

0.22

0.24

0.26

0.28

0.3

RC

H

mn

L

ConclusionConclusion

• The first example of where the Rc and screening models give different results!

• Screening explains the electron dynamics and the differences between linear and bent explosions.

• We have now recovered the ability to use ultrafast pulses to examine molecular structure.

• The first example of where the Rc and screening models give different results!

• Screening explains the electron dynamics and the differences between linear and bent explosions.

• We have now recovered the ability to use ultrafast pulses to examine molecular structure.

Acknowledgements

• Support NSF

• Graduate Students– Harry Zhao

– Vishal Chintawar

– J. Zhu

• Visitors– G. Zhang (Tianjian)

– F. Adameitz (France)

• Undergraduates– T. Colvin, Jr.

– D. Cofield

– D. Ellingston