Disentangling Competing Pathways in High-Energy Molecular Fragmentation

What is it about?

When a molecule is impacted by a high-energy particle, eg. a 70 eV electron, multiple fragment ions are formed. In such cases, there is a distinct possibility that a given fragment was formed via two different pathways. The key observation in this paper, is that each pathway can be associated with a coherent signature that the fragment yield acquires during the reaction. By mapping the coherence of each fragment ion, we show that it is possible to determine which pathway the fragments follow, and in some cases, we find that fragments were formed by two distinct pathways. This capability is demonstrated through the analysis of strong-field dissociative ionization of dicyclopentadiene, which proceeds through two distinct mechanisms: an intact-bridge pathway and a broken-bridge pathway. By distinguishing the coherent signatures associated with each, we can directly identify the competing routes leading to specific fragments, providing new insight into the dynamics of complex molecular ionization.

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Why is it important?

High-energy molecular fragmentation remains a challenging process to understand and accurately predict using current theoretical models. This study introduces an approach to disentangle competing reaction pathways in such complex processes, which frequently yield numerous fragment ions through multiple concurrent mechanisms.

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