We report two-dimensional electron energy-loss spectra of CO2 calculated within a four-dimensional nonlocal model for the vibronic dynamics involving two shape resonances (forming a Renner-Teller Πu doublet at the equilibrium geometry) coupled to a virtual Σþg state. The model elucidates the extremely non-Born-Oppenheimer dynamics of the coupled nuclear motion and explains the origin of the observed structures.
It is a prototype of the vibronic coupling of metastable states in continuum.