Ab initio investigation of the Auger spectra of methane, ethane, ethylene, and acetylene

We present an ab initio computational study of the Auger spectra of methane, ethane, ethylene, and acetylene. Auger spectroscopy is a established technique to probe the electronic structure of molecules and exploits the Auger-Meitner effect that coreionized states produced by X-ray irradiation undergo. We compute partial decay widths for the relevant decay channels using coupled-cluster theory with single and double substitutions (CCSD) and equation-of-motion-CCSD theory combined with complex-scaled basis functions and Feshbach-Fano projection. We generate Auger spectra from these partial widths and draw conclusions about the strength of particular decay channels and trends between the four molecules. A connection to experimental results about fragmentation pathways of the electronic states produced by Auger decay is also made.