Reaction of Phenyl Isocyanate and Phenyl Isothiocyanate with the Ge(100)-2 x 1 Surface

The adsorption of phenyl isocyanate and phenyl isothiocyanate at the Ge(100)-2 x 1 surface was probed using multiple internal reflection Fourier transform infrared (FUR) spectroscopy, density functional theory (DFT), and X-ray photoelectron spectroscopy (XPS). Results for phenyl isocyanate indicate that the saturation product is a [2 + 2] cycloaddition reaction product across the C=N bond, forming a surface-bound carbonyl. DFT reveals that this is the most stable of the expected products, and its calculated vibrational spectrum agrees closely with experimental spectra. FTIR spectroscopy studies of phenyl isothiocyanate reveal multiple surface adducts, with the product of the [2 + 2] cycloaddition reaction across the C=S bond as the major species and the product of the [2 + 2] cycloaddition reaction across the C=N bond as a minor product. In addition to these products, an excess of sulfur measured by XPS indicates the presence of a dissociative desorption product. The DFT calculated pathways and vibrational spectra for phenyl isothiocyanate confirm the FTIR and XPS assignments, and suggest the 1,3-dipolar cycloaddition product as a potential pathway for dissociative desorption.