Fig. 1.

IR and Raman (Right Inset) spectra of mixed silicalite and CO₂, showing evidence of the chemical reaction. The main figure shows IR spectra in the frequency region of the (ν₃ + ν₁; ν₃ + 2ν₂) combination band of CO₂. (Right Inset) Raman spectrum in the frequency region of the ν₊ line of CO₂, measured before the heating. Asterisks indicate peaks of CO₂ confined in the micropores of silicalite. The stronger peaks are from bulk, free CO₂ (see text). The sample was heated to 600 K for about 1 h. IR spectra before (after) the heating were measured upon increasing (decreasing) pressure. Changes in the line-shape of the band of bulk CO₂ are related to phase transitions among phases I, II, III, and IV of molecular CO₂ (1, 18). (Left Inset) Schematic representation of the crystal structure of silicalite.