THE ADSORPTION OF PYRAZINE, HYDROGEN-SULFIDE AND THIOPHENE ON COPPER - A QUANTUM-CHEMICAL STUDY

The bonding of pyrazine (C4H4N2), hydrogen sulfide (H2S) and thiophene (C4H4S) to copper surfaces has been examined employing semi-empirical MO-SCF calculations (INDO/S) and metal clusters of limited size (Cun n = 14, 16, 17 and 18). The C4H4N2Cu, H2SCu and C4H4SCu 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, H2S 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 CN, CC and CH bonds of pyrazine, the CS, CC and CH bonds of thiophene, and the SH bonds of H2S are examined. The large reactivity of H2S on copper surfaces is explained in terms of a thermochemical analysis. © 1990.