ELECTROCHEMICAL TUNING OF THE LIFETIME OF THE CO STRETCHING VIBRATIONFOR CO PT(111)/

We have used the large electric fields at the interface of a Pt(111) e lectrode and an acetonitrile electrolyte solution to tune the interact ion between adsorbed CO and the Pt(111) surface. The electrode potenti al is varied over a 2.5 Volt range. As the electrode potential is made more positive, the CO vibrational frequency increases and the vibrati onal lifetime decreases. Over the potential range investigated, the tu ning is about 35-40 cm(-1) and the lifetime varies from approximate to 2.1 to approximate to 1.5 ps. Ab initio calculations performed for CO /Cu(100) predicted the opposite trend for the lifetimes for that syste m [M. Head-Gordon and J. C. Jully, Chem. Phys. 175, 37 (1993)]. Within an empirical model of nonadiabatic charge transfer [B. N. J. Persson and M. Persson, Solid State Commun. 36, 175 (1980)], our observations can be explained by a decreasing 2 pi-derived density of states of the Pt/CO complex at the Fermi level. (C) 1996 American institute of Phys ics.