Interaction Between Donors and Acceptors on Metal Surfaces
We discuss the nature of the interaction between donor and acceptor molecules coadsorbed on metal surfaces. First, the recent experimental result is reviewed for the coadsorption of carbon monoxide (CO) with ammonia (NH3) and with methylamine (NH2-CH3). There seems to exist mutual attraction between CO and ammonia (methylamine) which is typical for the coadsorption of donor and acceptor molecules, where donors (acceptors) denote molecules which donate (accept) electrons through molecule-substrate bonding. We propose a model for the interaction among donors and acceptors based on the concepts of mutual polarization enhancement and depolarization. This model predicts that the donor-acceptor interaction not only causes mutual attraction between a donor and an acceptor but also enhances adsorptive bonding of both molecules. Several experimental results for the CO+ammonia, CO+benzene, and NO+benzene systems are discussed as evidence for this model. We also discuss direct interaction between molecular orbitals of coadsorbed molecules.
KeywordsMolecular Orbital Acceptor Molecule Ammonia Molecule Mutual Attraction LEED Pattern
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