X‑ray Scattering and O–O Pair-Distribution Functions of Amorphous Ices

The
structure factor and oxygen–oxygen pair-distribution functions
of amorphous ices at liquid nitrogen temperature (T = 77 K) have been derived from wide-angle X-ray scattering (WAXS)
up to interatomic distances of r = 23 Å, where
local structure differences between the amorphous ices can be seen
for the entire range. The distances to the first coordination shell
for low-, high-, and very-high-density amorphous ice (LDA, HDA, VHDA)
were determined to be 2.75, 2.78, and 2.80 Å, respectively, with
high accuracy due to measurements up to a large momentum transfer
of 23 Å–1. Similarities in pair-distribution
functions between LDA and supercooled water at 254.1 K, HDA and liquid
water at 365.9 K, and VHDA and high-pressure liquid water were found
up to around 8 Å, but beyond that at longer distances, the similarities
were lost. In addition, the structure of the high-density amorphous
ices was compared to high-pressure crystalline ices IV, IX , and XII,
and conclusions were drawn about the local ordering.