Direct measurement of core-level relaxation dynamics on a surface- adsorbate system

Electronic coupling between an adsorbate and the surface on which it resides is fundamental to the understanding of many surface interactions. However, the interaction of \textit{highly-excited} adsorbate states is an area that has been explored only indirectly to-date. In this work, we present the first direct time-resolved observations of the lifetime of core-excited states of an atom adsorbed onto a surface. By implementing laser-assisted Auger decay on an adsorbate/surface system, we directly measure the lifetime of the 4d$^{-1}$ core level of Xenon on Pt(111) to be 7.1 $\pm$ 1.1 fs. This result opens up time domain measurements of highly-excited state dynamics in materials systems where, because of complex interactions, energy-resolved measurements provide incomplete information.