AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Invited Paper SS1-TuM5
Formation of C-H and N-H bonds on the Pt(111) Surface as Studied with Reflection Absorption Infrared Spectroscopy

Tuesday, November 1, 2005, 9:40 am, Room 202

Session: Vibrational Spectroscopy of Surfaces
Presenter: M. Trenary, University of Illinois at Chicago
Authors: R. Deng, University of Illinois at Chicago
E. Herceg, University of Illinois at Chicago
K. Mudiyanselage, University of Illinois at Chicago
J. Jones, University of Illinois at Chicago
M. Trenary, University of Illinois at Chicago
Correspondent: Click to Email
The reaction of hydrogen with atomic species adsorbed on transition metal surfaces is a key step in many important catalytic processes. However, many surface probes are not sensitive to hydrogen so the detection and characterization of processes in which hydrogen forms bonds to other elements on surfaces has been difficult. Recent advances in the sensitivity of surface infrared spectroscopy allows surface intermediates with very weak IR absorption bands to be unambiguously detected. It is well known that the complete dehydrogenation of various hydrocarbons eventually leads to graphitic monolayers on platinum surfaces, although the exact forms of the surface carbon prior to graphite formation are still undetermined. Surface carbon has been prepared by the dehydrogenation of ethylene and acetylene on Pt(111) through exposure at 750 K. Subsequent hydrogen exposure leads to clear infrared features due to methylidyne (CH), ethylidyne (CCH@sub 3@), and ethynyl (CCH). These results demonstrate that C atoms and C@sub 2@ molecules exist as stable species on the surface. An ordered (2x2) layer of N atoms can be prepared on Pt(111) through the oxidation of ammonia in which all of the hydrogen and oxygen are removed through the desorption of water. Subsequent hydrogen exposure leads to a sharp and intense infrared band at 3320 cm@sup -1@ due to the NH species. Quantitative determinations of the NH and N coverages through temperature programmed desorption measurements indicate that only a small fraction of the surface N atoms are reactive towards hydrogen. The NH species can not be further hydrogenated to NH@sub 2@ or NH@sub 3@ under the conditions used in these experiments.