The structure of solid CO2 in porous Vycor glass

The structure of solid CO2 confined in porous Vycor glass has been studied as a function of temperature via x-ray diffraction. The confined solid has the same structure as the bulk solid but with a slightly larger lattice constant of 5.644 Angstrom at 150 K compared to the bulk lattice constant of 5.624 Angstrom at the same temperature. Broad diffraction peaks are observed indicating that the solid phase of the CO2 in the pores forms in small crystallites approximately 160 Angstrom in diameter. This is comparable to the pore dimensions in the Vycor indicating that solidification occurs separately in each of the pores. A large temperature-independent static disorder, analogous to the Debye-Waller factor, was observed in the form of strong damping of the Bragg peaks with increasing Q.