Observation of K-shell resonances in Xe and XeF2

We recently reported on the ion charge states and fragmentation channels of Xe and XeF₂ following K-shell x-ray absorption by the Xe atom. The ion spectra reveal effects of resonant excitations despite the 11.49-eV lifetime width of the vacancy states. Due to the high electronegativity of the F ligands, Xe forms stable molecules such as XeF₂. With 10 valence electrons, XeF₂ is a prime example of a hypervalent molecule and its structure has attracted interest since its discovery in the 1960s. A strong pre-edge resonance is observed in the x-ray absorption spectrum that we attribute to the antibonding 7σ_u orbital. Excitation of the 7σ_u resonance selects a spatially aligned ensemble of molecules as observed in our ion fragmentation spectra. Analysis of the x-ray absorption spectrum also yields a measurement of the chemical shift of the Xe 1s ionization energy resulting from the F ligands. Results of new measurements on Xe and XeF₂ with an improved x-ray/ion coincidence instrument will also be reported.

This work was supported by the Chemical Sciences, Geosciences, and Biosciences Division and the Advanced Photon Source by the Office of Basic Energy Sciences, Office of Science, US Dept of Energy, Contract DE-AC02-06CH11357.