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

We present a microscopic theory to describe the dynamics of STM-induced C2HD rotation on Cu(100). In our model, two intermediate processes, which lead to C2HD rotation, are taken into account when an electron initially transfers/tunnels from the STM tip to the adsorbate and then, subsequently, to the metal substrate. In one process, excitation of the hindered rotational mode occurs without CH(D) stretching vibrational excitation. In the other process, excitation of the CH(D) stretching vibrational mode occurs first and then, with the relaxation of the excited stretching vibrational mode, excitation of the hindered rotational mode. C2HD rotation to another equilibrium position on Cu(100) occurs when the excitation of the hindered rotational mode exceeds some threshold energy. The calculated rotation probabilities satisfactorily reproduce the experimental results.