It was demonstrated experimentally and by spectral simulation that the adsorbed organic monolayers on the substrate showing a very strong absorption in the region of the characteristic vibrations of the surface species can be studied successfully by the infrared external reflection technique. This technique allowed examining in detail the nature and structure of xanthate (CH3CH2OCS2- ) adsorbed layer on copper-activated quartz. There is a very strong variation of optical properties of quartz in the region of Si-O stretching vibration including the refractive index of quartz close to 0 between 1250 and 1100 cm(-1). These dramatic chances in the optical properties produce different optical effects, and for this reason, the reflection spectra of the adsorbed layer can be divided in three characteristic parts: (i) above 1250 cm(-1), (ii) between 1250 and 1100 cm(-1), and (iii) below 1060 cm(-1). Above 1250 cm(-1), a now band at about 1360 cm(-1) is observed because of the pure optical effect caused by the refractive index of quartz crossing the value of 1.0. This optical effect, "substrate band", is very sensitive to the thickness of the adsorbed layer and was utilized in this work for the determination of the patch-like structure of the produced adsorbed layer. In the second region between 1250 and 1100 cm(-1), where the refractive index of quartz is close to 0, only the electric field vector component parallel to substrate interface ((E-x(2) for p polarization) shows significant value, and as a consequence, only molecular vibration parallel to interface can be monitored for p polarization. This important finding is exactly reverse to the phenomenon observed at metal interfaces in the infrared region where practically only the vertical vibration (strong E-z(2)) component) could be spectrally monitored and is known in the literature as the "surface selection rule". Hence, a "reverse surface selection rule" could be Postulated for the adsorbed species investigated in the region of strong absorbance of substrate at refractive index significantly lower than 1.0. The highest spectral sensitivity to monitor the adsorbed species was found at the lowest incident angles (close to zero), which is another reverse observation compared to metal substrates where a grazing incident angle is recommended as the most sensitive spectral condition. In the third region below 1060 cm(-1), complex optical effects are observed resulting from a sharp decrease of the refractive index of quartz from a value around 5 to 2. It can be subdivided in two parts: (i) a higher refractive index (more than 3) that results in positive absorbance bands below Brewster angle and (ii) a lower refractive index that results in negative absorbance bands below Brewster angle. Another important phenomenon that has a strong effect on the recorded reflection spectra at higher incident angles is a strong shift of the Brewster angle with wavenumber. All of these complex optical effects were identified and described. This allowed interpreting properly the spectroscopic data and in consequence to describe in detail the surface phenomena that take place during the formation of the xanthate adsorption layer on copper-activated quartz. This work shows that the complex optical phenomena taking place during reflection of an incident beam in a stratified system are an enormous source of detailed information on the nature and structure of the produced surface layer even in such difficult systems with overlapping of very low signal from adsorbed species with very strong absorbance of substrate.