Imaging Acetylene Dynamics with Cross-Polarized Pulse Pairs

We investigate the strong-field driven rovibronic motion in acetylene that gives rise to unique phenomena such as enhanced ionization and isomerization. We use strong-field ionization to both initiate and probe these molecular dynamics with 6-fs cross-polarized pulse pairs. The two pulses initiate and probe dynamics in ionized acetylene, respectively, at a variable delay. Beyond characterizing the laser-induced motion in ionized acetylene, we gain insight into the polarization dependence of each of the strong-field processes. By reconstructing the full three dimensional time resolved ion momentum distributions, we are able to identify the critical molecular geometries, time delays, and orientations with respect to the polarization that give rise to these effects. This allows us to image the rovibronic motion which leads to isomerization and enhanced ionization of the molecule. Varying the delay between the pulses also enables the characterization of effects that may be caused by changes in the symmetry of the highest occupied molecular orbital. After multiple ionization, acetylene exhibits vibrational motion in the CC triple bonds and CH single bonds that can drive hydrogen migration, transient vinylidene formation, H2 elimination, and enhanced multiple ionization. Our results show that cross-polarized pulse pairs can reproduce all of these phenomena and furthermore, allow a better understanding of their dependence on the polarization of the driving fields.