Acetylene adsorption studies on Pd(111) and stepped Pd(111)

The adsorption of acetylene on Pd(111) and stepped Pd(111) surfaces as well as the influence and mechanism of a monatomic step have been investigated by theoretical calculations. On ideal Pd(111), the favourite acetylene adsorption site is the threefold hollow site. Our calculated geometry configuration and vibrational frequencies of adsorbed acetylene are consistent with previous studies. Generally speaking, steps have active effects, zero effects or inactive effects in the adsorption process. For acetylene on stepped Pd(111), a monatomic step as the active site makes the C-C bond of acetylene further weakened. Acetylene adsorption geometry in the second case (C-C bond axis tilts to the surface normal and the molecular plane is vertical to the step direction) is similar to that of the molecule on the Pd(110) surface because of the (110) structure of the step. Furthermore, the vibrational frequencies of acetylene are also in agreement with the results of HREELS studies of acetylene on Pd(110).