1. I. Bocharova L. Cocke, I. Litvinyuk, A. Alnaser, C. Maharjan, D. Ray
Using COLTRIMS for pump-probe studies of molecular dynamics
I. Bocharova
L. Cocke, I. Litvinyuk, A. Alnaser, C. Maharjan, D. Ray

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

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

4. Coulomb explosion imaging
Originally developed for investigation of a static structure: collision of molecular ions beam and thin foil
Accelerator Coulomb Explosion Imaging
Laser Coulomb Explosion Imaging
Now using laser short pulses interacting with molecules in gas phase

5. 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 D2
Exp. >40fs
Exp. 8fs
Theory: 4 fs

6. 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.

7. Experimental setup Gas jet Piezoelectric slit Laser pulse
Recoil side of
spectrometer x y z
Recoil detector
Piezoelectric
slit
Laser pulse M

8. Looking for explosion fragments in coincidence
Energy, eV
Magnitude of vector sum of all fragments momenta (a.u.)

9. Pump-probe

10. Pump-probe setup d θ d Pump pulse Probe pulse d pump-pulse probe-pulsex
probe-pulse

11. (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

12. D2 experment S(E,t) (2) D++D+ Dt D2+(X2Sg+) (1) D2 (X1Sg+)
KER at fixed delays
D2+(X2Sg+) Dt
D++D+
S(E,t)
D2 (X1Sg+)
(1)
(2)
pump
probe

13. 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.

14. D2: theory and experiment
Theoretical calculation: Xiao-Min Tong, C.D. Lin

15. H2 experiment
KER (eV)
DELAY (fs) 10 20
100 50
KER (eV)
DELAY (fs)

16. N2 and O2 experiment O2+5 O2+4 O2+3 O2+2 O2+ O2 PIPICO O+O+ TOF 2 (ns)
1000
2000
3000
2800
TOF 2 (ns)
O+O+
O2+O+
O2+O2+
O3+O2+
O3+O3+ O2
O2+
O2+2
O2+5
O2+4
O2+3
1000
2000
2800
TOF 1
N+N+
N2+N+
N2+N2+
N3+N+
N3+N2+
N3+N3+
N4+N2+
N4+N3+
3000
1000
100
TOF 2 10 1

17. KER Spectra for Oxygen O3+ + O2+ Pair O2++ O2+ Pair KER (eV)40 80
150
200
600
1000
DELAY (fs) 50
100
400
O3+ + O2+ Pair
KER (eV)

18. KER Spectra for Nitrogen1
TOF 1
TOF 2
1000
100 10
PIPICO
2000
2800
N+N+
N2+N+
N2+N2+
N3+N+
N3+N2+
N3+N3+
N4+N2+
N4+N3+
3000 40 80 70 60
120
KER (eV)
DELAY (fs)
N2++N2+ pair
N3++N2+ pair

19. 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 H
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, (2003).

20. C2H2 acetylene and vinylidene channels separation
CH+ + CH+
CH2+ + C+
C2+ + C+
C2+ + C2+
C2H+ + H+
C2+ + H+
TOF1
TOF2
pz (a.u.)
px (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)

21. Continue experiments with N2 and O2. CO2: triatomic molecule.
Future plans
C2H2 experiment.
Continue experiments with N2 and O2.
CO2: triatomic molecule.

22. Thank you!