Intra- and intermolecular effects in the Compton profile of water

The electron momentum density of water is measurable in an inelastic x-ray scattering experiment in the form of the Compton profile. The fine details of the profile, accessible by using high-brilliance synchrotron radiation, are sensitive to the precise intra- and intermolecular geometries. We present a detailed quantitative computational study of the sensitivity of Compton scattering to the different terms arising from the intramolecular structure, nearest-neighbor interactions (hydrogen bonds), and many-body properties (cooperativity and anticooperativity effects). The Compton profile is found to be predominantly sensitive to the internal O-H bond length and the hydrogen bond geometry, being less affected by the internal H-O-H angle and the many-body properties. In addition, an approximative method is introduced to provide a practical scheme for calculating larger water aggregates.