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

Using the transmission high-energy electron diffraction technique, we study the temperature dependence of the diffraction reflection intensities from the solid phase of CO2. To deduce absolute values of the orientational order parameter, we modify the existing reconstruction method to take into account the triatomic shape of the molecule. It is shown that for triatomic solids a higher-rank order parameter, eta(4), is important and cannot be neglected. Application of the modified approach yield eta and eta(4) values as a function of temperature over the range from 6 to 70 K. Both orientational order parameters prove to be a nonmonotone function of temperature. (c) 2007 American Institute of Physics.