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When silica is subjected to a vacuum degassing at about 600 °C two new infrared bands are observed at 908 and 888 cm""1 and the intensity of these bands increases with higher degassing temperature reaching a maximum at about 1200 °C. These bands are associated with the formation of a new active site on to which pyridine and trimethylamine can reversibly coordinate without dissociation of the site or of the adsorbate. It is suggested that a surface silicon atom of strained siloxane bridge is electron deficient thereby acting as a Lewis acid center. The nature and unusual chemical reactivity of this site are discussed in the following

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