THE STRUCTURE OF SOLID CO2 IN POROUS VYCOR GLASS

The structure of solid CO2 confined in porous Vycor glass has been stu died as a function of temperature via x-ray diffraction. The confined solid has the same structure as the bulk solid but with a slightly lar ger lattice constant of 5.644 Angstrom at 150 K compared to the bulk l attice constant of 5.624 Angstrom at the same temperature. Broad diffr action peaks are observed indicating that the solid phase of the CO2 i n the pores forms in small crystallites approximately 160 Angstrom in diameter. This is comparable to the pore dimensions in the Vycor indic ating that solidification occurs separately in each of the pores. A la rge temperature-independent static disorder, analogous to the Debye-Wa ller factor, was observed in the form of strong damping of the Bragg p eaks with increasing Q.