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.