Electron-mediated phonon-phonon coupling drives the vibrational relaxation of CO on Cu(100)

TL;DR

This paper develops a theory explaining how electron-mediated phonon-phonon interactions influence vibrational relaxation of CO molecules on Cu(100), highlighting the importance of electron-phonon coupling over traditional anharmonic effects.

Contribution

It introduces a comprehensive nonadiabatic theory that accurately models vibrational linewidths and temperature dependence, surpassing existing theories in explaining experimental observations.

Findings

Strong electron-mediated coupling between CO vibrational modes.

Significant role of surface motion in vibrational relaxation.

Theory matches experimental linewidths and temperature dependence.

Abstract

We bring forth a consistent theory for the electron-mediated vibrational intermode coupling that clarifies the microscopic mechanism behind the vibrational relaxation of adsorbates on metal surfaces. Our analysis points out the inability of state-of-the-art nonadiabatic theories to quantitatively reproduce the experimental linewidth of the CO internal stretch mode on Cu(100) and it emphasizes the crucial role of the electron-mediated phonon-phonon coupling in this regard. The results demonstrate a strong electron-mediated coupling between the internal stretch and low-energy CO modes, but also a significant role of surface motion. Our nonadiabatic theory is also able to explain the temperature dependence of the internal stretch phonon linewidth, thus far considered a sign of the direct anharmonic coupling.