Characterization of electron momenta in the strong-field enhanced ionization of water*

Photoionization of gas phase molecules can cause structural rearrangement due to electron density changes. Strong-field-induced double ionization of water has been shown to drive rapid dissociation pathways that lead to molecular geometries with a decreased tunneling barrier, a phenomenon known as enhanced ionization. While current understanding of the enhanced ionization process in water has been informed by measurements of the product ion momenta, the picture is incomplete. Here, we study the electrons produced in enhanced ionization using few-cycle pulse pairs at variable delay, measuring both the ionic and electronic fragments using a voltage-switching velocity map imaging apparatus. Covariance mapping correlates the emitted electrons with their corresponding ionic fragments on an event-by-event basis, revealing the full momentum picture of the dication dynamics.