Iron pentacarbonyl has been used as a novel probe molecule in investigations of the surface state of gold Au/SiO2 solids prepared by means of sol–gel procedures. The use of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveals that there is a strong interaction between Fe(CO)5 and the Au centers. The adsorption of Fe(CO)5 on a reduced Au/SiO2 sample is characterized by IR absorption bands at 2013 and 2032cm−1. With an oxidized sample, two additional bands at 2026 and 2040cm−1 are seen, attributed to the between Fe(CO)5 and oxidic gold sites. The results of density functional theory (DFT) calculations support the assignments of the IR absorption bands.