Photon-number-resolved asymmetric dissociative single ionization of H2

The electron-nuclear joint energy spectrum allows one to unambiguously count the total number of photons absorbed by the electrons and nuclei of a molecule. Driven by phase-controlled, linearly polarized two-color femtosecond laser pulses, we experimentally demonstrate that the asymmetric bond breaking of a singly ionized H2 depends on the total number of photons absorbed by the molecule in the ionization and dissociation processes. The accessibilities of different dissociation pathways and their interference-induced asymmetric electron localization as a function of the absorbed photons are retrieved. Our results strengthen the understanding of the directional bond breaking of a molecule from the aspect of the correlated electron-nuclear dynamics.