I. Bocharova

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Using COLTRIMS for pump-probe studies of
molecular dynamics

• I. Bocharova
• L. Cocke, I. Litvinyuk, A. Alnaser, C. Maharjan,
  D. Ray

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Outline

• Motivation
• Coulomb explosion imaging.
• Experiment requirements.
• Experimental setup.
• H2 and D2 experiments.
• N2 and O2 experiments.
• C2H2 experiment.
• Future plans.

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Motivation

• To study the structure and its time evolution of
  different gas molecules, using Coulomb explosion
  imaging

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Coulomb explosion imaging
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Why Coulomb explosion imaging?

• Direct method which allows for best time
  resolution can use short pulses ? Possible to
  observe molecules with fast dynamics such as D2

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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.

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Experimental setup
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Looking for explosion fragments in coincidence
Energy, eV
Magnitude of vector sum of all fragments momenta
(a.u.)
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Pump-probe
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Pump-probe setup
d
d
pump-pulse
probe-pulse
d
d
pump-pulse
?
x
probe-pulse
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(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.

e-
R0
Rc
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D2 experment
KER at fixed delays
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D2 KER vs Delay spectrum
R, a.u.
Long pulse (30fs) CREI
counts
KER, eV
Laser parameters pump 8fs 3x1014 W/cm2
probe 8fs 9x1014 W/cm2.
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D2 theory and experiment
Theoretical calculation Xiao-Min Tong, C.D. Lin
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H2 experiment
KER (eV)
DELAY (fs)
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N2 and O2 experiment
1000
100
TOF 2
10
1
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KER Spectra for Oxygen
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KER Spectra for Nitrogen
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C2H2 polyatomic molecule
C2H2 isomerization of acetylene to vinylidene
Time scale? the upper limit established is 60
fs1 H-CC-H ? H-CC-H2 ? CH CH
? C
CH2 Idea With short pulses pump-probe technique
can be applied to follow the dynamics of
isomerization process.
acetylene
vinylidene
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).
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C2H2 acetylene and vinylidene channels separation
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)
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Future plans

• C2H2 experiment.
• Continue experiments with N2 and O2.
• CO2 triatomic molecule.

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Thank you!