Local work-function changes of Pt(111) studied by STM and IRAS:: coadsorption of Cl- with H3O+, NO, and CO molecules

The coadsorption of chloride anion (Cl-) with hydronium cation (H3O+), nitrogen monoxide (NO), and carbon monoxide (CO) on Pt(lll) was studied in an ultra-high-vacuum system using scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRAS), and low-energy electron diffraction (LEED). HCl molecules adsorbed on Pt(lll) at 100 K form a (3 x 3) structure (theta (Cl)- = 0.44). Water adsorption on the 3 x 3 structure produces c(4 x 2)-(Cl- + H3O+) coadsorption structures. The hydronium cation adsorbs through oxygen lone pair, and hydrogen bonding (O-H . . . Cl) extends on the surface with these structures. Stretching absorption bands of NO (or CO) adsorbed on the 3 x 3 - Cl- and c(4 x 2)-(Cl- + H3O+) adlayers on Pt(lll) show remarkably higher and lower frequency shifts, respectively. The frequency shifts can be explained by the local charge density states of platinum atoms derived From electron withdrawal or supply from the coadsorbates (Cl- or H3O+) to platinum atoms. (C) 2000 Elsevier Science B.V. All rights reserved.