i. bocharova l. cocke, i. litvinyuk, a. alnaser, c. maharjan, d. ray
DESCRIPTION
Using COLTRIMS for pump-probe studies of molecular dynamics. I. Bocharova L. Cocke, I. Litvinyuk, A. Alnaser, C. Maharjan, D. Ray. Outline. Motivation Coulomb explosion imaging. Experiment requirements. Experimental setup. H 2 and D 2 experiments. N 2 and O 2 experiments. - PowerPoint PPT PresentationTRANSCRIPT
I. BocharovaL. Cocke, I. Litvinyuk, A. Alnaser, C. Maharjan, D. Ray
Outline
Motivation Coulomb explosion imaging. Experiment requirements. Experimental setup. H2 and D2 experiments. N2 and O2 experiments. C2H2 experiment. Future plans.
Motivation
To study the structure and its time evolution of different gas
molecules, using Coulomb explosion imaging
Coulomb explosion imaging
Originally developed for investigation of a static structure: collision of molecular ions beam and thin foil
Accelerator Coulomb Explosion Accelerator Coulomb Explosion ImagingImaging
Ultrathinfoil Detector
MeVbeam
Explodingmolecule
Laser Coulomb Explosion ImagingLaser Coulomb Explosion Imaging
Detector Detector
Now using laser short pulses interacting with molecules in gas phase
Why Coulomb explosion imaging?
5 10 15 20 250
200
400
600
800
1000
1200
1400
coun
ts
Energy, eV
D2 8 fs pulse
D2 30 fs pulse
0.5 1.0 1.5 2.0 2.5 3.0 3.50
2
4
6
R / Angstrom
||2
Direct method which allows for best time resolution : can use short pulses Possible to observe molecules with fast dynamics such as D2
D2
Exp. >40fsExp. 8fs
Theory: 4 fs
D2
+
pote
nti
al
ener
gy
internuclear distance
pump
D2
D+ + D
D+ + D+
KE
R
Requirements
Laser impulse shorter than vibration period of molecule.
High intensity to produce highly charged states, so explosion potential can be approximated by Coulomb potential.
Minimize the thickness of molecular target beam, so that interaction volume is minimal.
Experimental setupGas jet
Recoil side of spectrometer
x
y
z
Recoil detector
Piezoelectric slit
Laser pulse
M
Looking for explosion fragments in coincidence
En
ergy
, eV
Magnitude of vector sum of all fragments momenta (a.u.)
Pump-probe
E
Probe Pum p
Probe Pum p
W eak pum p pulseexcites m o lecule
D e lay a llow stim e evolution
In tense probepu lse ion izesm o lecu le
M o lecu le explodes
E
E
t
t
Pump-probe setup
d
pump-pulse
θprobe-pulse
d
x
d
pump-pulse
probe-pulse
d
)φcos(
)φθcos(11
)φcos(
1ndOPΔ
c
OP
n
sinarcsin
θ
d
d
Pump pulse
Probe pulse
(CR)EI – (Charge Resonance) Enhanced Ionization
Diatomic molecule: double well potential.
Picture is asymmetric in laser field.
R0 is an interatomic distance for neutral molecule.
Distance R between two centers increases.
At some critical distance Rc enhanced ionization occurs.
R0
Rc
e-
D2 experment
2 4 6 8 10 12
0
5
10
15
20
25
30
coun
ts
KER, eV
delay 0_10fs
2 4 6 8 10 12
delay 10_20fs
2 4 6 8 10 12
delay 20_30fs
D2+(X2g+)
t
D++D+
S(E,t)
D2 (X1g+)
(1)
(2)
t
pum
ppr
obe
KER at fixed delays
2 4 6 8 10 12
delay 30_40fs
2 4 6 8 10 12
delay 40_50fs
D2 KER vs Delay spectrum
R, a.u.
Laser parameters: pump 8fs 3x1014 W/cm2
probe 8fs 9x1014 W/cm2.
KER, eV
cou
nts
Long pulse (30fs) CREI
D2: theory and experiment
Theoretical calculation: Xiao-Min Tong, C.D. Lin
H2 experiment
DELAY (fs)
KE
R (
eV)
KE
R (
eV)
DELAY (fs)
0
10
20
0 10050 0 10050
0
10
20
N2 and O2 experimentPIPICO
1000
2000
3000
1000 2000 2800
TO
F 2
(ns) O+O+
O2+O+
O2+O2+
O3+O2+
O3+O3+
O2
O2+
O2+2
O2+5
O2+4
O2+3
1
TO
F 2
1000
100
10
1000 2000 2800
TOF 1
N+N+
N2+N+
N2+N2+
N3+N+
N3+N2+
N3+N3+
N4+N2+N4+N3+
3000
1000
2000
KER Spectra for Oxygen
O2++ O2+ Pair
0
40
80
0 80 150
200
600
1000
DELAY (fs) DELAY (fs)0
50
100
080 150
200
400
600
O3+ + O2+ Pair
KE
R (
eV)
KER Spectra for Nitrogen
1
TOF 1
TO
F 2
1000
100
10
PIPICO
1000 2000 2800
N+N+
N2+N+
N2+N2+
N3+N+
N3+N2+
N3+N3+
N4+N2+N4+N3+
3000
1000
2000
0
40
80
40
0
70
60 120 60 120
KE
R (
eV)
DELAY (fs) DELAY (fs)
N2++N2+ pair N3++N2+ pair
C2H2 : polyatomic molecule
C2H2 : isomerization of acetylene to vinylidene Time scale? the upper limit established is 60 fs1
H-CC-H [H-CC-H]2+ CH+ + CH+
C+ + CH2+
Idea: With short pulses pump-probe technique can be applied to follow the dynamics of isomerization process.
C C
C
CH H
H
H
1 T. Osipov, C. L. Cocke, M. H. Prior, A. Landers, Th. Weber, O. Jagutzki, L. Schmidt, H. Schmidt-Böcking, and R. Dörner, Phys. Rev. Lett. 90, 233002 (2003).
acetylene
vinylidene
C2H2 acetylene and vinylidene channels separation
CH
+ + CH +
CH
2 + + C+
C2+ + C
+C2+ + C
2+
C2 H + + H +
C2 + + H +
TOF1
TO
F2
pz (a.u.)
p x (a
.u.)
Momentum-imaging investigations of the dissociation of D2+ and the isomerization of acetylene to vinylidene by intense short laser pulses. A. S. Alnaser, I. Litvinyuk, T. Osipov, B. Ulrich, A. Landers, E.Wells, C. M. Maharjan, P.Ranitovic, I. Bocharova, D.Ray and C.L.Cocke. Journal of Physics B: Atomic, Molecular & Optical Physics. (accepted)
Future plans
C2H2 experiment.
Continue experiments with N2 and O2.
CO2: triatomic molecule.
