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Physical review letters 123(19), 193001 (2019). doi:10.1103/PhysRevLett.123.193001, We investigate K-shell ionization of N2 at 40 keV photon energy. Using a cold target recoil ionmomentum spectroscopy reaction microscope, we determine the vector momenta of the photoelectron, theAuger electron, and both Nþ fragments. These fully differential data show that the dissociation process ofthe N2þ2 ion is significantly modified not only by the recoil momentum of the photoelectron but also by thephoton momentum and the momentum of the emitted Auger electron. We find that the recoil energyintroduced by the photon and the photoelectron momentum is partitioned with a ratio of approximately30∶70 between the Auger electron and fragment ion kinetic energies, respectively.We also observe that thephoton momentum induces an additional rotation of the molecular ion., Published by APS, College Park, Md.

Physical review letters 118(3), 033202 (2017). doi:10.1103/PhysRevLett.118.033202, The hitherto unexplored two-photon doubly excited states [Ne*$(2p−^13s)]_2$ were experimentallyidentified using the seeded, fully coherent, intense extreme ultraviolet free-electron laser FERMI. Thesestates undergo ultrafast interatomic Coulombic decay (ICD), which predominantly produces singly ionizeddimers. In order to obtain the rate of ICD, the resulting yield of $Ne^+_2$ ions was recorded as a function ofdelay between the extreme ultraviolet pump and UV probe laser pulses. The extracted lifetimes of the long-lived doubly excited states, $390(−130/+450) $fs, and of the short-lived ones, less than 150 fs, are in goodagreement with $ab$ $initio$ quantum mechanical calculations., Published by APS, College Park, Md.