Hydrogen-Bonding in Liquid Water at Multikilobar Pressures.

High-precision THz (30 to 360 cm-1) spectra of bulk liquid water are presented from ambient conditions up to hydrostatic pressures of 10 kbar. In concert with ab initio simulations, this allows us to characterize the molecular-level changes of the H-bond network under solvent stress conditions. Both the experimental and theoretical THz spectra reveal a blue shift in the intermolecular translational mode at 180 cm-1 by 40 cm-1 at 10 kbar and a blue shift together with an intensity increase in the relaxation mode. These changes can be traced back to a pressure-induced increase of the population of so-called short H-bond double donor configurations at the expense of those with longer such intermolecular bonds. Distinct electronic polarization effects are critical to capture the characteristic intensity changes of the THz line shape function. These advances in high-pressure THz spectroscopy open the door to investigate the pressure response of solvation shells and solute-solvent couplings.