Angle- and internuclear separation- resolved strong field processes in molecules Grad student: Li Fang Funding : NSF-AMO May 26, 2010 DAMOP Houston, TX George N. Gibson University of Connecticut Department of Physics

Introduction A standard sample of molecules will be in their equilibrium configuration and randomly oriented. A standard sample of molecules will be in their equilibrium configuration and randomly oriented. However, strong field molecular processes depend on the orientation and alignment of the molecule and the inter-nuclear separations. However, strong field molecular processes depend on the orientation and alignment of the molecule and the inter-nuclear separations. We start with this: We would like this:

Control Methods One can control inter-nuclear separation by ionizing to dissociating states. However, several states are usually populated, one must work in an ion, and the dissociation happens quickly. Also, one can’t study the neutral molecule. One can control inter-nuclear separation by ionizing to dissociating states. However, several states are usually populated, one must work in an ion, and the dissociation happens quickly. Also, one can’t study the neutral molecule. Alignment can be controlled through adiabatic fields or impulsive techniques, but often the degree of alignment in not very high, unless multiple pulses are used, or the sample is not field-free. Alignment can be controlled through adiabatic fields or impulsive techniques, but often the degree of alignment in not very high, unless multiple pulses are used, or the sample is not field-free.

Resonant excitation provides an interesting alternative Using pump-probe techniques, we can control R. Resonant excitation follows a cos(  ) 2 pattern, producing a well-aligned and well-defined sample. This gives: = 0.6 at room temperature with one laser pulse. = 0.6 at room temperature with one laser pulse. [For unaligned samples = 0.33]

Wavepacket motion independent of angle

Ionization to I 2 +

Ionization vs. R We know from the motion on the B state. We know from the motion on the B state. Can convert from time to R(t). Can convert from time to R(t).

R c of a neutral excited state R c is at 8.6 a.u. Appears to increase with angle or decreasing field along the axis. Ionization potential increases with R in contrast to H 2 +, which decreases with R. PRA 59, 4843 (1999).

Hydrogen curves

Polar plots of ionization from the I 2 B 3  u + state to I 2 + Shows  u symmetry

Polar plots of ionization from the I 2 B 3  u + state to I 2 +

Ionization to I 2 2+

Polar plots of ionization to I 2 2+

Conclusions Resonant short-pulse excitation Provides high degree of alignment Provides high degree of alignment Provides controlled internuclear motion Provides controlled internuclear motion Allows us to measure ionization rates as a function of angle and R Allows us to measure ionization rates as a function of angle and R Possible coupling between angle and R Possible coupling between angle and R Mechanism for R c in an excited neutral? Is it just 1 electron in a double well, or do the ionic states play a role? Mechanism for R c in an excited neutral? Is it just 1 electron in a double well, or do the ionic states play a role?