Covalency of the hydrogen bond in ice: A direct x-ray measurement

Periodic intensity variations in the measured Comptori profile anisotropies of ordinary ice Ih correspond to distances of 1.72 and 2.85 Angstrom, whic h are close to the hydrogen bond length and the nearest-neighbor O-O distan ce, respectively. We interpret this result as direct evidence for the subst antial covalent nature of the hydrogen bond. Very good quantitative agreeme nt between the data and a fully quantum mechanical bonding model for ice Ih and the disagreement with a purely electrostatic (classical) bonding model support this interpretation and demonstrate how exquisitely sensitive Comp ton scattering is to the phase of the electronic wave function. [S0031-9007 (98)08227-1].