strong-field imaging of molecular dynamics wendell t. hill, iii university of maryland department of...
Post on 21-Dec-2015
217 views
TRANSCRIPT
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Zhang and Hill, unpublished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