Scattering Response of Sucrose Clusters with Intense XFEL Pulses in Water Window

We present a combined experimental and theoretical study about the effects of non-linear x-ray ionization dynamics on the scattering response of molecular clusters in the soft x-ray regime that includes and goes beyond the water window.~ Nanosized sucrose clusters were irradiated with intense XFEL pulses (photon energy from 500 to 1500 eV and pulse duration of 180 fs).~~ Surprisingly, the measured scattering signals near the oxygen K-edge in the water window are found to be substantially smaller than those at higher photon energies.~ We employ Monte-Carlo/Molecular Dynamics calculations to investigate the x-ray processes as a function of pulse parameters (photon energy, bandwidth and pulse duration) and cluster size.~ We demonstrate the important role of resonant excitation (RE) in the molecular scattering response in the water window.~ In particular, 1s -\textgreater 2p RE cycling enabled in the oxygen atom/ion provide additional ionization pathways which, combined with the long pulse duration, lead to substantial reduction in scattering power of sugar clusters for photon energies just below the oxygen K-edge.