The adsorption of pyrazine, hydrogen sulfide and thiophene on copper: A quantum-chemical study

Abstract

The bonding of pyrazine (C 4H 4N 2), hydrogen sulfide (H 2S) and thiophene (C 4H 4S) to copper surfaces has been examined employing semi-empirical MO-SCF calculations (INDO/S) and metal clusters of limited size (Cu n n = 14, 16, 17 and 18). The C 4H 4N 2Cu, H 2SCu and C 4H 4SCu adsorption bonds are mainly a product of the interaction of the 4s and 4p orbitals of the substrate with the LUMO and the sulfur or nitrogen lone pairs of the adsorbate. Based on these INDO/S results, the UPS spectra of pyrazine, H 2S and thiophene on copper surfaces are discussed and compared with experimental results. For each adsorbed molecule, charge transfers important to the change in work function are presented. The effects of chemisorption upon the CN, CC and CH bonds of pyrazine, the CS, CC and CH bonds of thiophene, and the SH bonds of H 2S are examined. The large reactivity of H 2S on copper surfaces is explained in terms of a thermochemical analysis.