Initial adsorption sites of CO on Pt(111) and Ni(100) at low temperature

Abstract

Adsorption of CO on Pt(111) at 25 K and Ni(100) at 18 K has been studied by infrared reflection absorption spectroscopy (IRAS). The occupation ratio of terminal CO to bridged CO species on Pt(111) at 25 K ranges from ∼2.3 to 1.2 at total coverages from 0.03 to 0.13 ML, and that of bridged CO to terminal CO species on Ni(100) at 18 K ranges from ∼3.2 to 0.7 at total coverages from 0.003 to 0.15 ML. Such strong coverage dependence of the occupation ratio, even at small coverages, suggests that the substrate-mediated interaction between CO molecules operates at a relatively long range ( > 10 A ̊ ). The isotope experiments suggest that there is dynamic interaction between preadsorbed (accommodated) CO species and incoming (mobile) CO species.