Figure 5.

IR spectroscopy indirectly detects the adsorbate-induced mobility of the Cr(II) sites at the silica surface. (a) IR spectra of Cr(II)/SiO₂ and of the bare silica support in a spectral region dominated by the overtones and combinations of the fundamental (SiO₄) vibrations of bulk silica. (b) Spectrum of Cr(II)/SiO₂ after subtraction of that of silica and that of the same sample interacting with CO either at room temperature or at 100 K. (c) The same as (b) for another Cr(II)/SiO₂ sample, before and after a short interaction with ethylene at room temperature. Unpublished data.