ECAMP 15

A dimer system can undergo ultrafast symmetry breaking by charge localization upon ionization. Our recent work explored symmetry braking dynamics in the Van der Waals bound $CO_2$ dimer using EUV pump - EUV probe Coulomb explosion imaging.[1] Here, I will present the symmetry breaking dynamics of a prototypical hydrogen bounded formic acid $(FA)$ dimer. Similar to DNA base pairs, the $FA$ dimer is bound by two hydrogen bonds, which form the ring-structure. Dimers in a neat $FA$ molecular beam were probed by EUV pump- near IR probe 3D coincidence imaging. Transient enhancement of protonated formic acid cation signal with $~150 fs$ lifetime was observed. Ab initio molecular dynamics simulations predict ionization- induced symmetry breaking in the $FA$ dimer ion ground state that results in ultrafast proton transfer concerted with opening of the dimer ring structure. Moreover, our coincidence analysis combined with theoretical simulations revealed the ultraslow delayed dissociation of dimer cation to $FAH^+$ and $FA-H$ product on the $µs$ timescale. Two- and three-body Coulomb explosion channels of $FA$ dimer dication will also be discussed.

[1] E. Livshits et al., Symmetry-breaking dynamics of a photoionized carbon dioxide dimer, Nat Commun 15, 6322 (2024).