Observation of \textit{K}-shell resonances in Xe and XeF$_2$*

We recently reported on the ion charge states and fragmentation channels of Xe and XeF$_2$ following \textit{K}-shell x-ray absorption by the Xe atom [1]. 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 XeF$_2$. With 10 valence electrons, XeF$_2$ 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 7$\sigma_u$ orbital. Excitation of the 7$\sigma_u$ resonance selects a spatially aligned ensemble of molecules as observed in our ion fragmentation spectra [1]. 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 XeF$_2$ with an improved x-ray/ion coincidence instrument will also be reported.\\[4pt] [1] R. W. Dunford \textit{et al.}, Phys. Rev. A \textbf{86}, 033401 (2012).