Infrared Reflectance Spectra of Carbon Monoxide Adsorbed on Nickel and Rhodium (110) Surfaces in High and Ultrahigh Vacua

Abstract

The research reported herein represents our efforts towards optimization of the experimental parameters for the purpose of obtaining infrared spectra of adsorbed species on clean, oriented metal films under reproducible and readily interpretable conditions. Spectra were obtained in the region 4000–50 cm−1. A narrow band due to physically absorbed or weakly chemisorbed CO on nickel (110) was found at 2056 cm−1, with a full width at half-maximum (fwhm) of about 10 cm−1 and a reflection maximum at 2038 cm−1. The corresponding isotopic (13C) CO absorption was located at 1998 cm−1. These absorptions could not be observed with certainty for pressures of CO below 0.5 torr. At lower pressures, reflectance changes indicated the presence of CO, but definite absorptions were not identified due to the lower signal-to-noise ratio and background variations. The fundamental of chemisorbed CO on rhodium (110) was observed as a doublet at 2078 and 2060 cm−1 (fwhm, 10 cm−1 for each component) with a reflection maximum at 2030 cm−1. A further weak absorption attributed to adsorbed CO was found at 1988 cm−1 on rearranged films. The bands remained undiminished upon evacuation at room temperature. These and other observations of the systems are discussed and compared with results found in the literature.