Charge Resonance Enhanced Ionization of Probed by Laser Coulomb Explosion Imaging

The process by which a molecule in an intense laser field ionizes more efficiently as its bond length increases towards a critical distance is known as charge resonance enhanced ionization (CREI). We make a series of measurements of this process for , by varying pulse duration from 7 to 200 fs, in order to identify the charge states and time scales involved. We find that for the and higher charge states, 100 fs is the time scale required to reach the critical geometry and ⟨𝜃OCO⟩ ≈163 ° (equilibrium CO2 geometry is ⟨𝑅CO⟩ ≈1.16  Å and ⟨𝜃OCO⟩ ≈172 °). The CO3+2 molecule, however, appears always to begin dissociation from closer than 1.7 Å indicating that dynamics on charge states lower than 3 + is not sufficient to initiate CREI. Finally, we make quantum ab initio calculations of ionization rates for CO2 and identify the electronic states responsible for CREI.