The influence of the anomalous dispersion on the appearance of reflection-absorption bands in the infrared (RAIR) is evaluated, and quantitative trends concerning optically induced peak shifts for the analysis of reflection spectra are presented. We measured RAIR spectra and optical response functions of several trialkoxysilanes. In particular, we present results for (3-aminopropyl)triethoxysilane. Calculations of RAIR spectra demonstrate the influence of the anomalous dispersion on the appearance of band contours of Si-O modes. As a result, peak positions in reflection spectra do not always correlate with transmission reference data, because these optical effects are absent in the latter. We solve this problem by transforming transmission spectra into reflection spectra. These calculated reflection spectra serve as reference for the identification of experimental reflection spectra. Alkoxysilanes also undergo hydrolysis and condensation reactions that cause additional shifts of Si-O band positions.