Orientational order parameter in CO₂-based alloys with rare gases from THEED data: pure CO₂

Abstract

Using the transmission high-energy electron diffraction technique, we studied the temperature dependence of the diffraction reflection intensities from the solid phase of CO₂. To deduce absolute values of the orientational order parameter, we modified the existing reconstruction method to account for the triatomic shape of the molecule. It is shown that for triatomics solids a higher-rank order parameter, n4, is important and cannot be neglected. Application of the modified approach yielded n and n₄ values as a function of temperature over the range from 6 to 70 K. Both orientational order parameters proved to be a nonmonotone function of temperature.