Symmetry-breaking dynamics of a photoionized carbon dioxide dimer

Photoionization can initiate structural reorganization of molecular matter and drive formation of new chemical bonds. Here, we used time-resolved extreme ultraviolet (EUV) pump - EUV probe Coulomb explosion imaging of carbon dioxide dimer ion $$ dynamics, that combined with ab initio molecular dynamics simulations, revealed unexpected asymmetric structural rearrangement. We show that ionization by the pump pulse induces rearrangement from the slipped-parallel (C_2h) geometry of the neutral $$ dimer towards a T-shaped (C_2v) structure on the ~100 fs timescale, although the most stable slipped-parallel (C_2h) structure of the ionic dimer. Moreover, we find that excited states of the ionized $$ dimer can exhibit formation of a $$ moiety in the $$ complex that can persist even after a suitably time-delayed second photoionization in a metastable $$ dication. Our results suggest that charge asymmetry plays an important role in the ionization-induced dynamics in such dimers that are present in $$ rich environments.