Rotation of a single acetylene molecule on Cu(001) by tunneling electrons in STM

TL;DR

This study combines theoretical modeling and DFT calculations to explain how tunneling electrons induce rotation of a single acetylene molecule on Cu(001), matching experimental data and identifying key vibrational modes involved.

Contribution

It introduces a combined Keldysh-Green function and DFT approach to accurately reproduce and analyze STM-induced molecular rotation mechanisms.

Findings

Reproduces experimental rotation rates as a function of bias and current.

Identifies the reaction coordinate mode and its anharmonic coupling.

Explains rotation via excitation of C-H stretch, overtone ladder climbing, and combination band excitation.

Abstract

We study the elementary processes behind one of the pioneering works on STM controlled reactions of single molecules [Stipe et al., Phys. Rev. Lett. 81, 1263 (1998)]. Using the Keldysh-Green function approach for the vibrational generation rate in combination with DFT calculations to obtain realistic parameters we reproduce the experimental rotation rate of an acetylene molecule on a Cu(100) surface as a function of bias voltage and tunneling current. This combined approach allows us to identify the reaction coordinate mode of the acetylene rotation and its anharmonic coupling with the C-H stretch mode. We show that three different elementary processes, the excitation of C-H stretch, the overtone ladder climbing of the hindered rotational mode, and the combination band excitation together explain the rotation of the acetylene molecule on Cu(100).