Ultrafast Nuclear Dynamics in Double-Core Ionized Water Molecules

Double-core-hole (DCH) states in isolated water and heavy water molecules,resulting from the sequential absorption of two x-ray photons, have beeninvestigated. A comparison of the subsequent Auger emission spectra from thetwo isotopes provides direct evidence of ultrafast nuclear motion during the1.5 fs lifetime of these DCH states. Our numerical results align well with theexperimental data, providing for various DCH states an in-depth study of thedynamics responsible of the observed isotope effect.