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Research Highlights
Nicholas Camillone

 Ultrafast Surface Dynamics Group Research:

 • Testing The “Pseudo-Thermal” Model: CO Desorption from Pd

Because the (√3 × √3)R30° phase of carbon monoxide binds tightly to the (111) surface of Pd, it is a useful model system for testing the “pseudo-thermal” description of ultrafast photoinduced desorption. We have performed detailed measurements and modeling of the ultrafast photodesorption dynamics that indicate that the desorption is activated as in conventional thermal desorption. Further, we find that the same activation energy for desorption describes both the ultrafast and thermal (slow) processes.
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• Adsorption State Dependent Reaction Dynamics: O2 Desorption from Pd

We have investigated the adsorption-state-dependence of the substrate–adsorbate coupling responsible for the desorption of molecularly chemisorbed oxygen from the Pd(111) surface. By varying the amount of O2 on the surface we sequentially populated three adsorption states and measured their photoinduced desorption dynamics. Our model for the energy transfer from the surface to the adsorbate reveals that the more tightly bound the molecules are, the more efficient the electron-mediated energy transfer process.
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• Efficient Ultrafast Photoinduced Bimolecular Chemistry: CO Oxidation on Pd

As a step closer to the goal of time-resolving surface chemical reaction events, we have investigated the ultrafast photoinduced reaction of CO with atomic oxygen on the Pd(111) surface. Under UHV conditions Pd is an excellent thermal catalyst. We have found the ultrafast photoinduced oxidation also to be very efficient; the oxidized fraction of the desorbed molecules ranges from ~15% to 40%, approximately an order of magnitude greater than observed from Ru(001) under similar conditions. We also find that the dynamics are strongly dependent on the initial CO coverage in a manner consistent with an activation energy that depends on the initial CO binding site. Our results are consistent with the photooxidation occurring rapidly (within one to several picoseconds) from an initial mixed CO+O adlayer structure without time for diffusional phase segregation.
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Chemical Imaging Group Research:

• Manipulation of and Desorption from TiO2 surfaces

Stay tuned for new developments.

• Hot carrier dynamics

Stay tuned for new developments.

 
 

 Last update on: February 03, 2009