Study of double core holes in CO molecules created by intense short free electron laser pulses

The intense short x-ray laser pulses from the Linac Coherent Light Source sequentially double core-ionize CO molecules within the time scale of the Auger decay of the single-core-hole state, producing double core holes. We will present the evidence of double core holes located at different atomic sites in CO molecules via both Auger and photoelectron spectroscopy. The spectral features corresponding to the double core holes are consistent with our theoretical calculations, showing evidence of various site arrangement of multiple core holes. Our results prove experimentally the feasibility of double-core-hole spectroscopy as a new chemical analysis tool. This work was supported in part by the DOE-SC-BES. [1] L.~Fang \textit{et al.}, PRL \textbf{105}, 083005 (2010). [2] J.~Cryan \textit{et al.}, PRL \textbf{105}, 083004 (2010).