A structural study of very high-density amorphous ice

Neutron and X-ray structure factor functions of very high-density amorphous (VHDA) ice have been measured and compared with those of the high- and low-density amorphous forms. The principal peak in the VHDA structure factor is sharper than that observed in the HDA ice form. Radial distribution functions (rdfs) indicate the local O⋯O separation is 2.83 Å, close to 2.85 Å estimated from earlier Raman measurements, but larger than that observed by empirical potential structure refinement simulation of neutron data. Perhaps more importantly the rdfs indicate a greater extent of ordering in VHDA ice, with observable coordination shells extending to at least 20 Å.