Configurational Transitions of Benzene and Pyridine Adsorbed on Pt{111} and Cu{110} Surfaces: An Infrared Study

Abstract

Reflection−absorption infrared spectroscopy (RAIRS) is used to compare and contrast the coordination, bonding, and configurational transitions for benzene and pyridine adsorbed on Pt{111} and Cu{110}. Benzene adsorbs on both surfaces with its molecular plane parallel to the surface. As a result, the out-of-plane CH bending mode is the only IR-active mode observed on each surface. On Cu{110} a single absorption band is seen at around 680 cm-1, whereas on Pt{111} two bands are observed with frequencies of 900 and 830 cm-1 and the latter splits at high coverages. The differences are attributed to the relative strengths of the interaction of benzene with the two surfaces and the occupation of 3-fold and 2-fold adsorption sites. The adsorption of pyridine also shows distinct differences on the two surfaces. On Cu{110}, pyridine initially adsorbs with its molecular axis perpendicular to the surface plane, with vibrational frequencies similar to those of the free molecule. On Pt{111} the orientation of the molec...