Extended x-ray absorption fine structure from hydrogen atoms in water

We report the first quantitative measurement of extended x-ray absorption f ine structure (EXAFS) from hydrogen atoms. A single oscillation is observed from gaseous water consistent with the location of the covalently bonded h ydrogen in H2O. The experimental phase and amplitude of the oscillation are in excellent agreement with curved wave multiple scattering calculations f or isolated water molecules. With this determination of the O-H scattering phase shift we have quantified the covalent hydrogen bond distance (0.95 +/ - 0.03 Angstrom) in liquid water, thus demonstrating that hydrogen EXAFS ca n become a valuable complement to existing structural methods in chemistry and biology.