Specific chemical bond relaxation unravelled by analysis of shake-up satellites in the oxygen single site double core hole spectrum of CO2

We recently developed a method dubbed NOTA+CIPSI [A. Ferte, et al., J. Phys. Chem. Lett. 11, 4359 (2020)] to compute single site double core hole (ssDCH or K−2 ) spectra, that is now applied to the O K−2 spectrum of the CO2 molecule, and for which its convergence properties are discussed. Using this approach, we obtain a spectrum in excellent agreement with the experimental result. Thanks to a thorough interpretation of the shake-up states responsible for the main satellite peaks and with the help of a comparison with the O K−2 spectrum of CO, we can highlight the clear signature of the two non equivalent carbon oxygen bonds in the ssDCH CO2 dication.