We demonstrate that high resolution autoionization studies for core excitations under Auger resonant Raman (ARR) conditions can be used to extract extremely fast charge transfer (CT) relaxation times for chemisorbed molecules on a metal surface. For the $\mathrm{O}1s$ and $\mathrm{C}1s$ bound resonances of CO on Ru(0001), ARR behavior is almost completely suppressed; from its small remnant detectable by its linear dispersion with photon energy, CT times below 1 fs can be determined. For CO on a Xe spacer, only dispersive Raman-type decay is seen; i.e., no CT occurs.

• Received 11 August 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.1774