Photoinduced coherent adsorbate dynamics on a metal surface: Nuclear wave-packet simulation with quasi-diabatic potential energy curves using an open-boundary cluster model approach

We present a nuclear wave-packet simulation of photoinduced coherent adsorbate dynamics on a metal surface with quasi-diabatic potential energy curves obtained from our recently developed open-boundary cluster model approach. Photoexcitation to the resonant adsorbate state and the subsequent ultrafast decay to the electronically excited substrate states were found to cause a coherent vibration of the adsorbate on the metal surface. This process competes with a Raman scattering process, which is generally believed to explain the coherent adsorbate vibration. These two mechanisms induce vibrations with a common frequency, and therefore cannot be distinguished from each other in a frequency-domain experiment. However, they can be distinguished by determining the initial vibrational phase through a time domain experiment such as ultrafast pump-probe spectroscopy. We further demonstrate that for near-resonant excitation the oscillation amplitude induced by our proposed mechanism largely exceeds the amplitude due to the Raman mechanism.