Ethylene adsorption on Pd(111) studied using infrared reflection–absorption spectroscopy

The adsorption of ethylene has been studied on clean and hydrogen-covered Pd(1 1 1) using reflection–absorption infrared spectroscopy and molecular beam methods. Using a correlation diagram, in which vibrational frequencies are plotted versus a rp parameter proposed by Stuve and Madix, shows that ethylene is substantially rehybridized on Pd(1 1 1) having a rp parameter intermediate between those of ethylene on Ni(1 1 1) and Ru(0 0 1). In contrast, when ethylene adsorbs on hydrogen-covered Pd(1 1 1), only p-bonded species are detected. An additional species appears exhibiting a characteristic frequency of 957 cm 1 when Pd(1 1 1) is cooled to 80 K and the system pressurized with 10 5 Torr of ethylene. This species also appears on a CO-saturated Pd(1 1 1) surface. Molecular beam measurements show that its coverage reaches 1.3 ML indicating that it is due to ethylene adsorbed in the second and subsequent layers. 2002 Elsevier Science B.V. All rights reserved.