Dynamics of STM-induced acetylene rotation on Cu(100)

We present a microscopic theory to describe the dynamics of STM-induced C2H D rotation on Cu(100). In our model, two intermediate processes, which lead to C2HD rotation, are taken into account when an electron initially transf ers/tunnels from the STM tip to the adsorbate and then, subsequently, to th e metal substrate. In one process, excitation of the hindered rotational mo de occurs without C-H(D) stretching vibrational excitation. In the other pr ocess, excitation of the C-H(D) stretching vibrational mode occurs first an d then, with the relaxation of the excited stretching vibrational mode, exc itation of the hindered rotational mode. C2HD rotation to another equilibri um position on Cu(100) occurs when the excitation of the hindered rotationa l mode exceeds some threshold energy. The calculated rotation probabilities satisfactorily reproduce the experimental results. (C) 2000 Elsevier Scien ce B.V. All rights reserved.