Approaches for constraining uncertainty and degeneracy in geometry reconstruction of molecules from simulated Coulomb explosion data

Coulomb explosion imaging (CEI) data, consisting of atomic ion momenta, resulting from a rapid (few fs) ionization event, is typically recorded as a first step in the generation of a single molecule geometry measurement or the production of a ‘molecular movie’ that watches the evolution of an excited state geometry in time. Deriving a reliable geometry from this data is a crucial and challenging step, as unique solutions may not exist. In this work, we start by simulating the geometries of a molecule, which is out of equilibrium, the asymmetric carbonyl sulfide (OCS) molecule. We generate momentum data resulting from six-fold ionization and investigate two methods to reconstruct geometries. The first method is a look-up table, which is simple in principle but shows limitations in terms of accuracy and ability to identify multiple ‘degenerate’ solutions. The second is a new method using nonlinear constrained optimization …