The chemisorption of CO on Pd(110) at 110 and 300 K studied by electron energy loss spectroscopy

Abstract

The vibrational electron energy loss spectrum of CO adsorbed on Pd(110) at both 110 and 300 K has been recorded as a function of CO exposure. At both temperatures the spectra indicate that CO adsorption occurs predominantly in two-fold bridged sites along the rows of metal atoms. At 110 K the surface may be saturated to give a two-fold bridged (2 × 1) CO overlayer of p2mg unit mesh symmetry, yielding a LEED pattern with absences at the (± 1 2 h odd , 0) positions along the 〈110〉 azimuth. Near saturation, ( θ ≥ 1.0), a weak band due to CO adsrobed in on-top sites is observed. At 300 K, LEED studies show that a c(2 × 2) pattern forms at low exposures ( <1 L), followed by a p(4 × 2) pattern at higher exposures. The latter structure persists up to a dynamic CO pressure of 1 × 10 −7 mbar where an incomplete p2mg pattern forms, with residual four-fold periodicity along the rows of metal atoms. EEL spectra corresponding to the p(4 × 2) overlayer indicate that at least two distinct two-fold bridge CO species are present giving rise to νCO loss features separated by only 60 cm −1.