ABSTRACT
The authors have developed a new experimental approach for measuring gas-surface selective adsorption resonances with much higher energy resolution and over a wider range of kinematic conditions than has previously been possible. The technique involves using a 3He spin-echo spectrometer as a Fourier transform helium atom scattering apparatus. The authors applied the technique to the He-LiF(001) system. They developed a new empirical potential for the He-LiF(001) system by analyzing and refining the best existing potentials in the light of the new data set. Following an initial free-particle model analysis, the authors used exact close coupling scattering calculations to compare the existing potentials with the new experimental data set. Systematic differences are observed between the two. The existing potentials are modified by simple transformations to give a refined potential that is consistent with and fully reproduces the experimental data. Their technique represents a new approach for developing very high precision empirical potentials in order to test first principles theory.
ABSTRACT
We present momentum resolved measurements of quasielastic helium atom scattering made using a new 3He spin-echo spectrometer. Our data for the dynamics of CO on Cu(001) indicates an activated jump mechanism which we analyze in detail using molecular dynamics simulations. A nearly isotropic potential energy surface is found with an average barrier height of approximately 125 meV, yielding comparable hopping rates along both the <110> and <100> directions. The measurements provide the first rigorous experimental test of state-of-the-art first-principles calculations previously made on this system.
