The chemisorption of ethylene epoxide and carbonate on silver: A quantum-chemical study

Abstract

The chemisorption of carbonate (CO 3) and ethylene epoxide (C 2H 4O) on silver has been examined employing semi-empirical quantum-chemical calculations (INDO/S) and clusters of limited size (Ag 18). The results indicate that ethylene epoxide is an electron donor upon adsorption on Ag surfaces, with no contribution of the empty orbitais of the free molecule to the surface-adsorbate bond. Most of the charge transfer from ethylene epoxide toward the surface is from the occupied frontier orbitals: 2b 1 and 6a 1. The CO 3 group appears as a net electron acceptor (π-donor, σ-acceptor) when adsorbed on Ag(110). The influence of chemisorption effects upon the CO, CC and CH bonds of ethylene epoxide, and the CO bonds of carbonate are discussed. The bond order indices indicate that from the viewpoint of the substrate the Ag(5s, 5p) orbitals are primarily responsible for the chemisorption of ethylene epoxide and carbonate on silver surfaces. For each adsorbed molecule, charge transfers and dipole moments important to the change in work function are presented. Based on these INDO/S results, the UPS spectra of ethylene epoxide and carbonate on Ag(110) and the NEXAFS spectrum of carbonate on Ag(110) are discussed and compared with experimental results.