Calculation of scanning inelastic tunneling profiles of adsorbates: acetylene on Cu(100)

Several questions recently posed by Inelastic Electron Scanning Tunneling S pectroscopy (STM-IETS) experiments are clarified. First, the method of calc ulating inelastic currents as a function of the tip's position and the bias is shown, as well as how to relate the currents to experimental results. W e apply the method to calculate the rotation rate profile of the acetylene molecule on Cu(100) as a function of the tip's displacement. The fraction o f electrons inelastically scattered by the different vibrational modes of t he molecule is calculated also as a function of the bias, in a range of sev eral volts. The results of the calculation explain why the C-H bending mode s were not detected in STM-IETS experiments. (C) 2000 Elsevier Science B.V. All rights reserved.