Rotationally mediated focussed inelastic resonances in D-2 scattering from Cu(001)

We have observed the phenomenon of rotationally mediated focussed inelastic resonance (RMFIR) in the scattering of D-2 from Cu(001). The RMFIR effect is theoretically predicted to occur in the inelastic scattering of molecules for which surface bound states exist and consists of a phonon-assisted focusing of an appreciable fraction of an incident beam of arbitrary energy and direction into a final channel of a single well-defined energy and direction. Three resonance energies of -21.5, -13.4 and -10.3 meV are obtained from the observed RMFIR peaks. The bound states corresponding to these resonance energies are epsilon(0) = -28.9, epsilon(1) = -19.8 and epsilon(3) = -10.3 meV, respectively. Whereas the resonances at -12.4 and -10.3 meV contribute a sharp intensity enhancement at RMFIR conditions, the resonance at -21.5 meV yields a striking minimum which represents the first evidence of what we call a focussed inelastic anti-resonance.