Control of H2 Dissociative Ionization in the Nonlinear Regime Using Vacuum Ultraviolet Free-Electron Laser Pulses

In this work the sustained enhancement and control of the dissociative ionization (DI) / nondissociative ionization (NDI) ratio in the simplest of all molecules, H₂ was demonstrated experimentally for the first time. This increase by about 2 orders of magnitude results in DI probabilities even larger than those for NDI at certain excitation energies, which is a remarkable finding for single photoionization of small molecules. Electron and ion velocity map imaging (VMI) allows for the identification of the DI and NDI mechanisms, and a comparison with ab initio calculations enlightens the dynamics at play within the 100-fs pulse duration.