NEGATIVE-ION MEDIATED ELECTRON-STIMULATED DISORDERING OF C(8X2) BENZOATE-CU(110) - EXTENSION OF THE DISPLACED HARMONIC-OSCILLATOR MODEL

We have extended the displaced harmonic oscillator model for negative ion resonance (NIR) scattering in high-resolution electron energy loss spectroscopy (HREELS), to interpret the energy transfer processes lea ding to disordering in STM and LEED, by allowing the curvature of the negative ion PES to be different to that of the ground PES. For the be nzoate-Cu(110) system, the results of the extended model are significa ntly better if the ground and negative ion PESs have frequencies h ome ga=0.40 and 0.48 eV, respectively, rather than the same frequency. The large resonance width and asymmetry, but not the small overtone to fu ndamental excitation probability ratio, observed in HREELS can be acco unted for with values of the coupling constant, beta=22.2 and inverse lifetime of Gamma=0.6 eV (1.1 fs). These parameters, with n(D)=7 are s imultaneously able to account for the ratio of the STM:LEED disorderin g cross-sections and, most significantly, predict the large slope obse rved in the STM disordering cross-section as a function of bias. The p roperties of the probability distribution, P-n(epsilon(i)), for the NI R process, involving two Franck-Condon transitions, is contrasted with the DIET process and some non-classical behaviour for the case omega( 0) not equal omega(1) is noted. (C) 1997 Elsevier Science B.V.