Nuclear Motion in Water Ionized by 5-fs Strong Fields

Strong-field (multiple) ionization (SFI) experiments on molecules with small moments of inertia, such as water, have demonstrated that the large field strengths required for SFI can heavily modify the momenta of ionic fragments during the dissociation that follows multiple ionization. This has a profound effect on final state properties, such as the species, angular distribution, and kinetic energy of the fragments. We recently demonstrated that dynamic alignment and unbending are two dominant effects in the SFI of water for ionizing pulse durations of 40 fs (at 800 nm and 600 TW/cm²). These effects are significantly suppressed for ionizing pulse durations of 10 fs (at 780 nm and 400 TW/cm²). Here we show that dynamic rearrangement of molecular nuclei still occurs for pulse durations shorter than 10 fs. We compare the full three-dimensional fragment momentum distributions of multiply charged two- and three-body dissociations of H₂O, D₂O, and HOD for pulse durations from 5 fs to 20 fs, noting the changes in each molecule’s bend-angle and alignment with respect to the polarization and the redistribution of population between various decay channels.