Interpreting STM image and tunneling-current-induced rotation of cis-2-butene on a Pd(1 1 0) surface

Tunneling-current-induced rotation of a cis-2-butene molecule on a Pd(1 1 0) surface and its scanning tunneling microscopy (STM) image has been interpreted using STM image simulations. Theoretical simulations uniquely reproduced experimentally observed STM images allowing for the unambiguous identification of the binding configurations of adsorbed molecules and the origin of STM images. The asymmetrical oval shape in the images arises from the tilted binding configuration because the two CH3 groups contributed differently to the STM images. The tunneling-current-induced rotation between four equivalent binding configurations occurs according to two different rotational axes lying on the Pd(1 1 0) surface.