Nonadiabatic coupling between C-O stretching and Pt substrate electrons enhanced by frustrated mode excitations

Abstract

We report the transient enhancement of coupling between adsorbate internal stretching vibration and substrate electrons induced by femtosecond laser excitation. A Pt(111) surface covered with carbon monoxide (CO) is irradiated with a 150 fs pump pulse at 400 nm. Transient changes in the imaginary part of nonlinear susceptibility in the C-O stretching region are probed by using femtosecond time-resolved infrared-visible sum-frequency generation with phase-sensitive detection. The line shape of C-O stretching shows remarkable asymmetry due to Fano interference with a continuum of electron-hole pair excitation. Excitations of CO-Pt frustrated modes play a key role in the enhancement of the nonadiabatic coupling.