Diffraction study of solid oxygen embedded in porous glasses

Molecular oxygen condensed and solidified in porous silica with pore diameters of 5, 7.5, and 13 nm has been investigated by x-ray diffraction as function of the filling fraction and the temperature. Two components of the pore filling can be distinguished: an amorphous layer on the pore walls, about 2 ML thick, with no conspicuous temperature dependence and the capillary condensate in the pore center that shows the sequence liquid-γ-β of bulk O₂, but with reduced transition temperatures. In 5-nm pores the γ-β transformation is incomplete. In the larger pores remainders of the β-α transition have been detected.