Ab initio cluster model study of electric field effects for terminal and bridge bonded CO on Pt(100)

The ab initio cluster model approach has been applied to investigate the el ectric field effects for CO on on-top and bridge sites of the Pt(100) surfa ce modeled by Pt-41 and Pt-32. For the available experimental data in the a bsence of external electric fields, a reasonable agreement between experime ntal and calculated results is found for CO chemisorbed on Pt(100). Electri c field effects induce changes in the equilibrium distance and vibrational frequency of chemisorbed CO but also on the chemical bonding mechanism, in particular in the extent of the 2 pi* backdonation. The model calculations predict a linear relationship between the intensity of the electric field a nd the extent of the 2 pi* backdonation. The existence of this linear relat ionship means that a separation between electrostatic and chemical effects is not feasible. (C) 1999 Elsevier Science Ltd. All rights reserved.