X-ray Spectroscopy of Liquid Water Microjets

We present the first results from studies of liquid water microjets by soft X-ray absorption spectroscopy. Near the oxygen K-edge (~530 eV) a fine-structure pattern very similar to that found for gaseous water monomers is observed when the surface-selective total ion yield (TIY) is measured, but a broadened and blue-shifted spectrum emerges when detecting the bulk-sensitive total electron yield (TEY). TIY EXAFS measurements produce a nearest neighbor O−O distance for surface molecules (3.00 Å) slightly longer than that of the isolated water dimer (2.98 Å), whereas the O−O distance extracted from TEY EXAFS corresponds to that accepted for bulk water (2.85 Å). Together, these results evidence an equilibrium liquid water surface dominated by water molecules interacting weakly at longer distances than in the bulk, thus supporting predictions from computer simulations.