Attosecond impulsive stimulated x-ray raman scattering in liquid water

We report the measurement of impulsive stimulated x-ray Raman scattering in neutral liquid water. An attosecond pulse drives the excitations of an electronic wavepacket, which comprises two steps: a transition to core-excited states near the oxygen atoms accompanied by transition to a valence-excited states. Thus, the wavepacket is impulsively created at a specific atomic site within a few hundred attoseconds through a non-linear interaction between the water and the x-ray pulse. We observe this nonlinear signature in an intensity dependent Stokes Raman sideband at 526 eV. Our measurements are supported by our state-of-the-art calculations based on the polarisation response of water dimers in bulk solvation and propagation of attosecond x-ray pulses at liquid density.