We present a detailed analysis of the two-dimensional electron energy-loss spectrum of ${\mathrm{CO}}_2$, which extends our recent Letter [Phys. Rev. Lett. 129, 013401 (2022)]. We show that our vibronic coupling model [Phys. Rev. A 105, 062821 (2022)] captures primary features of the multidimensional dynamics of the temporary molecular anion, and the calculations qualitatively reproduce the spectrum. The shape of the spectrum is given by two overlapping contributions that originate in excitation of vibrational states within ${\mathrm{\Sigma }}_g^{+}$ and ${\mathrm{\Pi }}_u$ Fermi polyads. Propensity rules in terms of scattered and vibrational wave functions are also discussed to clarify the selectivity of states from the vibrational pseudocontinuum that is responsible for the observed fine structure.

• Received 8 October 2022
• Accepted 16 November 2022

DOI:https://doi.org/10.1103/PhysRevA.106.062807