Isotopic quantum effects on the structure of low density amorphous ice

Abstract

Careful neutron diffraction measurements on deuterated low density amorphous(LDA) ice confirm that at 120 K it can be considered a fully ‘annealed’ structure,as no significant changes are observed in the amorphous spectra untilcrystallization occurred over time at 130 K. On this basis, the measurement ofstructural differences between the hydrogenated and deuterated forms of LDA iceat 120 K, have been carried out using 98 keV electromagnetic radiation diffractiontechniques. The maximum observed isotope effect in LDA ice is ∼ 3.4%at 40 K when compared to the magnitude of the first peak inthe electronic structure factor at Q = 1.70 Å−1.This compares to a maximum effect of ∼ 1.6%previously measured in liquid water at room temperature (Tomberli et al 2000 J.Phys.: Condens. Matter. 12 2597). The isotope effect is shown to be similarto a temperature shift in the structure of light LDA ice. However, theexistence of a first sharp diffraction peak at Q = 1.0 Å−1 inthe isotopic difference function is not reproduced in the temperature differenceand suggests that additional longer-range correlations are present in the moreordered deuterated form.