Characterization of the carbon–silicon stretch in methylated porous silicon—observation of an anomalous isotope shift in the FTIR spectrum

The FTIR band corresponding to the Si–C stretch in methylated porous silicon shows an anomalous isotope shift for CD3 due to mixing of the stretch and the methyl rocking motion. The shift in the Si–C stretching frequency observed for 13CH3 is that expected for the change in reduced mass of the methyl group. The Si–C band is in a region (650–690 cm−1) where it will be obscured by residual Si–H bands unless alkylation proceeds to high coverage such as is observed upon methylation (ca. 80% replacement of Si–H). The Raman spectra of porous silicon and methylated porous silicon are reported, and it is shown that this technique is not significantly better than FTIR for the identification of the Si–C stretching band.