Ultrafast Transient Dynamics of Adsorbates on Surfaces Deciphered: The Case of CO on Cu(100)

TL;DR

This paper presents a first-principles theoretical framework that explains ultrafast transient vibrational spectral changes of CO on Cu(100) surfaces caused by femtosecond laser pulses, clarifying microscopic mechanisms.

Contribution

It introduces a novel computational approach that accurately describes nonthermal frequency and linewidth changes in surface adsorbates due to ultrafast laser excitation.

Findings

Electron-hole pair excitations cause nonthermal frequency shifts.

Electron-mediated vibrational coupling leads to linewidth changes.

The sequence of coupling events is precisely identified.

Abstract

Time-resolved vibrational spectroscopy constitutes an invaluable experimental tool for monitoring hot-carrier induced surface reactions. However, the absence of a full understanding on the precise microscopic mechanisms causing the transient spectral changes has been limiting its applicability. Here we introduce a robust first-principles theoretical framework that successfully explains both the nonthermal frequency and linewidth changes of the CO internal stretch mode on Cu(100) induced by femtosecond laser pulses. Two distinct processes engender the changes: electron-hole pair excitations underlie the nonthermal frequency shifts, while electron-mediated vibrational mode coupling gives rise to linewidth changes. Furthermore, the origin and precise sequence of coupling events are finally identified.