Infrared reflection absorption spectra of Fe(CO)(5) adsorbed on Au surfaces

Infrared reflection absorption spectroscopy (IRAS) shows that the C-O stretching bands of Fe(CO)(5) adsorbed on Au surfaces are significantly different in band shape as well as in frequency from the bands observed in a transmission mode. This difference has been observed for other metal substrates and explained in terms of the anomalous dispersion of the refractive index in the region of the observed bands. The refractive indices of Fe(CO)(5) are calculated using the Kramers-Kronig relation from the transmission spectra of Fe(CO)(5) adsorbed on a sapphire plate, an SiO2-coated sapphire plate, and an Au film evaporated on a sapphire plate, and the IRA spectra of Fe(CO)(5) adsorbed on Au are calculated using Fresnel's formula. The results show that the nu(10) band of Fe(CO)(5) becomes very sharp and shifts to higher frequencies by more than 10 cm(-1), while the nu(6) band becomes a shoulder of the nu(10) band, in good agreement with the observed IRA spectra. The IRAS calculation also shows that the weak band observed at 2114 cm(-1) for the Au film remains unchanged in position, in agreement with the observed IRAS.