Strong-Field Imaging of Molecular Dynamics Wendell T. Hill, III University of Maryland Department of Physics and Institute for Physical Science and Technology

Explosion Energies Light Atoms Heavy Atoms ~40% of E eq ~70% of E eq Normand, et al., PRA 53, R1958 (1996) Cornaggia, et al., PRA 44, 4499 (1991)

Enhanced Ionization at R c R = R eq R > R eq I FR/2 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)

H 2 Explosion Energy: Experiment Gibson, et al., PRL 79, 2022 (1997) Zuo and Bandrauk, PRA 52, R2511 (1995) Theory R c =4/I P (au) Zhang and Hill, unpublished

3-Atom Enhanced Ionization at R c R C  0.22 nm (4 au) E mea  66 e V nh + CO 2 O p+ + C q+ + O r+ No intermediate molecular states observed! p, q, r = 1,2,3

GENERIC XY 2 LINEAR POTENTIAL SURFACE Y+X+Y XY+Y Y+XY R1R1 R2R2

What about the electrons?

Dynamic Screening Explosion Model Ionization and Dissociation Interlaced Electrons do not leave region immediately! Dissociation R eq but slowed by electron cloud producing energies consistent with dissociation from R c. Brewczyk, Rzążewski and Clark PRL 78, 191 (1997) Hering, Brewczyk and Cornaggia, PRL 85, 2288 (2000)

Thomas-Fermi Hydrodynamic Model

Static Screening Model Zhao, Zhang and Hill, PRA (submitted) C O O Dynamic Screening Static Screening

Angular Dependence of E C

Time-Resolved Waveforms Digital Scope Acquisition Mass-Resolved Energies Distributions Time-Resolved Images 128 x 128 Pixels 730 Hz Digital Acquisition 500,000 – 1,000,000 Frames Mass-Resolved Energies & Angular Distributions Momentum & Time-of-Flight Spectra

14 (k) O – 820 ns (l) O – 870 ns (m) OH – 920 ns (n) N 2+,3+, O 2+, – 620 ns (o) All Ions All Time (f) N 2+, O – 570 ns (g) O – 620 ns (h) 570 – 670 ns (i) N – 720 ns (j) N – 770 ns (a) H – 210 ns (b) H – 310 ns (c) N – 420 ns (d) N 3+, O – 470 ns (e) N – 520 ns 10

Momentum Image 0 0 Momentum Scale: 5 – 8 amu/div POLARIZATION AXIS

Correlation Imaging AVERAGE IMAGE SELECTIVE AVERAGE POLARIZATION AXIS 0 1

Symmetric Coulomb Explosion NO 2 CO 2

Across O-O Through Minimum Over-the-Barrier Ionization

I = 1.75  W/cm 2, R = nm, s = 0.03 I = 1.66  10 14, R = nm, s = I = 3.29  W/cm 2, R = nm, s = Limits on Smoothing Factor

Along Saddle Points Across O-O Bond Enhanced Ionization at R c

Symmetric Explosion vs. Bond Angle NO 2 CO 2

Charge Density Parameters NO 2 CO 2 e-e- e-e- e-e- e-e- Resulting Charge Distribution Wider Distribution Larger y 0

NO 2 explosion range  b = ° CO 2 explosion range  b = ° Linear vs. Bent Explosions

Conclusion The first example of where the R c 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 R c 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