Abstract
Adsorption of ethene on clean and ethylidyne-covered Pt(111) surfaces was investigated by infrared reflection absorption spectroscopy (IRAS). Under gaseous ethene of ∼ 10 −3 Pa, π-bonded ethene was reversibly formed on a Pt(111) surface saturated with di-σ-bonded ethene at 112 K. The π-bonded ethene gave infrared absorption peaks at 954 and 3090 cm −1 which were assigned to CH 2 wagging (out-of-plane) and CH 2 asymmetric stretching modes, respectively. These two peaks indicated that the π-bonded ethene was adsorbed on Pt(111) in such a way that the molecular plane is tilted with respect to the surface while the CC bond is being kept parallel to the surface. The intensity of the CH stretching band at 2908 cm −1 of di-σ-bonded ethene decreased with the increase of π-bonded ethene. The heat of adsorption of π-bonded ethene was estimated to be 40 ± 10 kJ/mol. The presence of ethylidyne with saturation coverage was found to inhibit the π-bonded ethene adsorption.
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