Femtosecond Surface Vibrational Spectroscopy of CO Adsorbed on Ru(001) during Desorption

Using time-resolved sum-frequency generation spectroscopy, the C—O stretch vibration of carbon monoxide adsorbed on a single-crystal Ru(001) surface is investigated during femtosecond near-IR laser excitation leading to desorption. A large transient redshift, a broadening of the resonance, and a strong decrease in intensity are observed. These originate from coupling of the C—O stretch to low-frequency modes, especially the frustrated rotation, that are highly excited in the desorption process.