A FTIRAS Study of CO Adsorbed at Ni(100) Surfaces

Abstract

AbstractAdsorption of CO at Ni(100) surfaces has been studied with Fourier‐Transform Infrared Absorption‐Reflection (FTIRA) spectroscopy in the temperature range 121 K to 350 K. Up to a coverage of θ = 0.5 top site and bridge site bonded CO has been identified by absorption peaks in the frequency range 2016 to 2048 cm−1 and 1885 to 1949 cm−1, respectively. The site population is temperature dependent, top sites are preferred at high temperatures, bridge sites at low temperatures. Towards the saturation coverage, θ ≈︁ 0.67 the top site peak is replaced by a broad absorption structure between 2000 and 2100 cm−1, which contains at least 3 separate peaks. The bridge site related absorption remains a single peak but shifts upwards by 20 cm−1 to 1968 cm−1. This suggests that above a coverage of θ = 0.5 CO molecules are arranged in an incommensurate adsorption structure, in which a unique top adsorption site does no longer exist.