Periodic intensity variations in the measured Compton profile anisotropies
of ordinary ice Ih correspond to distances of 1.8 and 3.0 Angstrom, which a
re close to the hydrogen bond length and the nearest-neighbor O-O distance,
respectively. We interpret this result as direct evidence for the covalent
nature of the hydrogen bond. Very good quantitative agreement between the
data and a fully quantum mechanical bonding model for ice I-h, and the disa
greement with a purely electrostatic (classical) bonding model support this
interpretation and demonstrates how exquisitely sensitive Compton scatteri
ng is to the phase of the electronic wavefunction. (C) 2000 Published by El
sevier Science Ltd. Ail rights reserved.