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

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.

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 Imaging Laser Coulomb Explosion Imaging Now using laser short pulses interacting with molecules in gas phase

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

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

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

Pump-probe

Pump-probe setup d θ d Pump pulse Probe pulse d pump-pulse probe-pulse x 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. e- R0 Rc

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

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.

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

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

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

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)

KER Spectra for Nitrogen 1 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

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, 233002 (2003).

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)

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

Thank you!