Photo double-ionization of CO2 studied by photoelectron-photoelectron coincidence experiments at 20 eV excess energy in equal energy sharing conditions

The Triple-Differential Cross Section (TDCS) for the Photo Double-Ionization of carbon dioxide molecule to the CO₂²⁺ X³ Σ_g⁻ ground state has been measured at 20 eV excess energy. In the experiment the coincidence angular distributions of the two photoelectrons, where the direction of one photoelectron has been fixed at 0, 30 and 60° with respect to the direction of the polarization of the incident radiation, have been measured for a condition where the two photoelectrons equally share the excess energy. Care has been taken to perform the measurements with an energy resolution which enabled to isolate the TDCS of the X³Σ⁻_g ground state of the dication. An appreciable contribution to TDCS at a relative angle θ₁₂ = 180° has been observed and attributed to a favorite symmetry of the wavefunction of the two ejected electrons.

Graphical abstract

TDCS of CO₂ measures at photon energy 57.7eV, θ₁=0, 30 and 60° and equal energy sharing of 10 eV are reported as black dots. Panels (a) and (c) report the TDCS as calculated by Alwan et al. (J Phys B: At Mol Opt Phys 48:185203, 2015) using the charge in the Sommerfeld parameters for the oxygen atom of 0.2 (black full curve) and 0.8 (ref full curve). The blue full curve in panels (d)-(f) is the fit to the experiments with the helium=like model by Reddsih and Feaging (J Phys B: At Mol Opt Phys 32:2473, 1999).