Effects of laser pulse duration and intensity on Coulomb explosion of CO2: signatures of charge-resonance enhanced ionization

Synopsis We studied laser-induced Coulomb explosion of CO2 by full triple-coincidence momentum resolved detection of resulting ion fragments. From the coincidence momentum data we can reconstruct molecular geometry immediately before explosion. We observe the dynamics of Coulomb explosion by comparing reconstructed CO2 geometries for different Ti:Sapphire laser pulse durations (at the same intensity) ranging from few cycles (7 fs) to 200 fs. We conclude that for longer pulse durations (≥100 fs) Coulomb explosion proceeds through the enhanced ionization mechanism taking place at the critical O-O distance of 8 a.u., similarly to well known charge-resonance enhanced ionization (CREI) in H2. CREI at the critical internuclear distance is a well established mechanism for strong-field double ionization of hydrogen by sufficiently long (>20 fs) near-IR laser pulses [1, 2]. Whether a similar mechanism also operates during multiple ionization of larger molecules is still a matter of some debate. Here we present experimental evidence that multiple ionization of tri-atomic CO2 molecules by intens