Specific chemical bond relaxation unraveled by analysis of shake-up satellites in the oxygen single site double core hole spectrum of CO 2 .

We recently developed [A. Ferté, et al. , J. Phys. Chem. Lett. , 2020, 11 , 4359] a method to compute single site double core hole (ssDCH or K -2 ) spectra. We refer to that method as NOTA+CIPSI. In the present paper this method is applied to the O K -2 spectrum of the CO 2 molecule, and we use this as an example to discuss in detail its convergence properties. Using this approach, theoretical spectra in excellent agreement with the experimental one are obtained. Thanks to a thorough interpretation of the shake-up states responsible for the main satellite peaks and through 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 oxygen ssDCH CO 2 dication.