Polarized FTIR - Spectra of C 60 layers and adsorbates of CO and CO 2 on C 60

Abstract

Thin films of buckminsterfullerene C 60 were deposited on KBr(100) at 78 K that were prepared by cleaving in UHV. The thickness of the film was monitored by recording the IR spectrum of C 60 at different polarizations. For the first time FTIR spectra of CO and CO 2 adsorbed on C 60 film were measured under UHV conditions. At pressures <10 −9 mbar the transmission spectra of CO 2 adsorbed on the C 60 film at temperatures below 90 K show a single ν 3 absorption peak at 2328 cm −1 with a linewidth (FWHM) of 5 cm −1. At higher CO 2 pressures the coverage grows and the linewidth and intensity of the absorption peak increase. A second absorption peak at 2331 ± 1 cm −1 was detected. At still higher pressures multilayer adsorption takes place with absorptions at 2344 and 2380 cm −1 at p-polarization and 2344 cm −1 at s-polarization. A single absorption peak of CO adsorbed on C 60 was recorded in transmission at 2134 cm −1 with a linewidth of 5 cm −1 at temperatures below 40 K. With increasing CO pressure a peak shift to 2138 cm −1 and an enhancement of the linewidth to 10 cm −1 was observed. Still higher pressures lead to multilayer adsorption with absorptions at 2142 and 2139 cm −1 at p-polarization and 2139 cm −1 at s-polarization. All absorptions detected, including the C 60 spectra, possess higher intensities at s-polarization than at p-polarization. At an angle of incidence of 45° the ratio of the integrated absorption (A s/A p) at s-polarization and p-polarization respectively is 1.3.