AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM9
Direct Observation of Electron Emission from a Metal Surface Due to Scattering of Vibrationally Excited Molecules

Monday, November 15, 2004, 11:00 am, Room 210B

Session: Electronic Structure and Excitations
Presenter: J.D. White, University of California, Santa Barbara
Authors: J.D. White, University of California, Santa Barbara
J. Chen, University of California, Santa Barbara
D. Matsiev, University of California, Santa Barbara
D.J. Auerbach, Hitachi Global Storage Technologies
A.M. Wodtke, University of California, Santa Barbara
Correspondent: Click to Email
We report the observation of electron emission from low work function metal surfaces due to the scattering of highly vibrationally excited nitric oxide (NO) molecules. Using Stimulated Emission Pumping (SEP) and Franck Condon Pumping (FCP), we prepare NO in vibrational states ranging from v=1 to v=18. SEP allows us to control explicitly the final vibrational state (from v=4 to v=18) while FCP allows us to prepare a range of states (dependent on the Franck Condon Factors) from v=0 to v=5 in the Electronic Ground State. These molecules are then scattered off of a low work function surface (~1.3 - 1.6 eV), in our case submonolayer cesium on gold, and the emitted electrons are detected with a Multi Channel Plate assembly. Our experiments indicate that the observed particles are indeed electrons which are promptly emitted after collision of the vibrationally excited NO with the surface. Vibrational energy dependence experiments suggest a threshold for emission at roughly the work function of the surface. The maximum efficiency we have measured is approximately 0.02 electrons per molecule. Possible mechanisms for vibrationally induced electron emission are discussed. Our results are very important in determining the limitations of using the Born Oppenheimer Approximation (BOA) to model highly excited gas-surface reaction dynamics. The transition state for molecular dissociation very likely involves molecules stretched to large bond distances, which can be approximated by highly vibrationally excited molecules. Experiments along this vein will help to determine how accurate it is to use the BOA for modeling these systems.