CO on Pt(111) and stepped Pt(335) surfaces: Vibrational Stark effect and electron energy loss investigation

Thesis/Dissertation · Tue Dec 31 23:00:00 EST 1991

OSTI ID:7041882

Luo, J S

Three experiments were designed to clarify the source of a surprising difference observed earlier between the vibrational Stark shift of two different atom C[double bond]O stretch modes, CO on the step edge and CO on the (111) terrace, on the stepped Pt(335) surface. The observed data of CO on Pt(335) cannot be explained by a difference in intramolecular structure between the two CO species-a chemical mechanism. The electron energy loss spectroscopy (EELS) measurements for CO on Pt(335) indicate that any such differences are too small to account for the data. An alternative, physical mechanism has to be responsible. The observed Stark effect of CO on Pt(335) results from strong screening of the static field at terrace sites, even though no difference in the screening of the IR field is observed. The authors developed a model for the populations of four CO species versus coverage for CO on Pt(335), which plausibly accounts for our EELS and temperature programmed desorption data. Bridge-bonded CO is first observed on this highly stepped surface. The authors used reflection absorption infrared spectroscopy (RAIRS) and electroreflectance vibrational infrared spectroscopy (EVS) to confirm that the Stark shift of terrace CO on Pt(335) is significantly suppressed. The Stark shift of CO on Pt(111) is quite comparable to that of edge CO and is significantly bigger than that of terrace CO on Pt(335). In the same experiment, the authors observed that the screening effects for the IR field and the static field are fundamentally different. Most importantly, this result and the conclusion for CO on Pt(335) suggest that the present physical picture of electric field screening at surfaces is qualitatively wrong. The authors also found that our measured Stark shift of CO on Pt(111) in ultrahigh vacuum (UHV) is only one half that in electrochemical cells. Such a difference is possible related to extra screening of the static electric field in UHV.

• Research Organization: Michigan State Univ., East Lansing, MI (United States)
• OSTI ID: 7041882
• Country of Publication: United States
• Language: English

Related Subjects

664200* -- Spectra of Atoms & Molecules & their Interactions with Photons-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY LEVELS
ENERGY-LOSS SPECTROSCOPY
EXCITED STATES
METALS
OXIDES
OXYGEN COMPOUNDS
PLATINUM
PLATINUM METALS
SPECTROSCOPY
STARK EFFECT
SURFACE PROPERTIES
TRANSITION ELEMENTS
VIBRATIONAL STATES