Observation of multiple ionization pathways for OCS in an intense laser field resolved by three-dimensional covariance mapping and visualized by hierarchical ionization topology

The two- and three-body Coulomb explosion of carbonyl sulfide (OCS) by 7900.3em0exnm, 500.3em0exfs laser pulses focused to ≈10¹⁶0.3em0exW0.2em0excm^-2 has been investigated by the three-dimensional covariance mapping technique. In a triatomic molecule, a single charge state, in this case the trication, has been observed to dissociate into two distinct energy channels. With the aid of a three-dimensional visualization technique to reveal the ionization hierarchy, evidence is presented for the existence of two sets of ionization pathways resulting from these two initial states. While one group of ions can be modeled using a classical enhanced ionization model, the second group, consisting of mainly asymmetric channels, cannot. The results provide clear evidence that an enhanced ionization approach must also be accompanied by an appreciation of the effects of excited ionic states and multielectronic processes.