Method for acquiring low-frequency transmission infrared spectra of adsorbed compounds on silica gels

A transmission infrared technique for detecting bands due to adsorbed speci es on silica gels in the region 4000 to 200 cm(-1) is described. The region below 1300 cm(-1) contains strong Si-O bulk modes that dominate the much w eaker hands due to adsorbed species. Silica gels are strong infrared scatte rers, and adsorbed molecules lead to changes in the spectral artifacts in t he region containing the bulk modes. These artifacts dominate and mask out the much weaker bands due to adsorbed species. By embedding the silica gel in a pliable polymer film of similar refractive index, one minimizes the ar tifacts, enabling detection of bands attributed to adsorbed compounds.