Ultrafast Lasers and Molecular Dynamics: Time-Resolving Orbital Structure and Ionization with Velocity Map Imaging

We investigate the molecular dynamics of an excited state in I$_{\mathrm{2}}$ using ultrafast lasers in a pump-probe measurement and record the data with a velocity map imaging (VMI) detector. The 45 fs (1fs $=$ 10$^{\mathrm{-15}}$ s) pump pulse at 513 nm resonantly excites the molecule to the B state of I$_{\mathrm{2}}$ producing a vibrational wave packet (VWP) with a period around 700 fs. The evolution of the VWP is then probed with a 45 fs pulse at 800 nm which ionizes the B state to the dissociating (2,0) channel of I$_{\mathrm{2}}^{\mathrm{2+}}$. By varying the time delay between the pump and probe pulses we are able to resolve the vibrational motion and record the kinetic energy release and angular distribution of the B state with the VMI. This powerful technique allows for direct study of the angular distribution of the excited B state and further allows us to take ``images'' of the molecular orbital as it dissociates. In particular, we wish to study the ionization of the B state as a function of internuclear separation, R, to see how the molecular orbital changes throughout dissociation. These ultrafast techniques will be reviewed and some preliminary results will be presented.