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We investigate K-shell ionization of N$_2$ at 40 keV photon energy. Using a COLTRIMS reaction microscope we determine the vector momenta of the photoelectron, the Auger electron and both N$^+$ fragments. These fully differential data show that the dissociation process of the N$_2^{2+}$ ion is significantly modified not only by the recoil momentum of the photoelectron, but also by the photon momentum and the momentum of the emitted Auger electron. We find that the recoil energy introduced by the photon and the photoelectron momentum is partitioned with a ratio of approximately 30/70 between the Auger electron and fragment ion kinetic energies, respectively. We also observe that the photon momentum induces an additional rotation of the molecular ion., Comment: 5 pages, 2 figures

We investigate the differential ionization probability of chiral molecules in the strong field regime as a function of the helicity of the incident light. To this end, we analyze the fourfold ionization of bromochlorofluoromethane (CHBrClF) with subsequent fragmentation into four charged fragments and different dissociation channels of the singly ionized methyloxirane. We observe a variation of the differential ionization probability in a range of several percent. Accordingly, we conclude that the helicity of light is a quantity that should be considered for the theoretical description of the strong field ionization rate of chiral molecules., 12 pages, 6 figures, submitted

The hitherto unexplored two-photon doubly-excited states [Ne$^{*}$($2p^{-1}3s$)]$_{2}$ were experimentally identified using the seeded, fully coherent, intense extreme ultraviolet free-electron laser FERMI. These states undergo ultrafast interatomic Coulombic decay (ICD) which predominantly produces singly-ionized dimers. In order to obtain the rate of ICD, the resulting yield of Ne$_{2}^{+}$ ions was recorded as a function of delay between the XUV 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 good agreement with \emph{ab initio} quantum mechanical calculations.

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 / A 90(1), 013416 (2014). doi:10.1103/PhysRevA.90.013416, Angular distributions of the N2O+(X) and N2O+(A) photoelectrons were measured as functions of the exciting-photon energy with small bandwidth in the vicinity of the resonant Nt(1s→π∗), Nt(1s→σ∗), and Nc(1s→π∗) core excitations of N2O. For selected exciting-photon energies in this range, angular distribution parameters of the N2O+(A→X) fluorescence were also determined. These data are interpreted by ab initio calculations. Long-range exciting-photon energy dependencies of the photoelectron angular distribution parameters βeX(ω) and βeA(ω), recorded vibrationally unresolved, are attributed to an electronic state interference between the direct and the different resonant amplitudes for the population of the final ionic states. In addition to that, strong influence of lifetime vibrational interference is identified in the observed dispersion of the vibrationally resolved fluorescence angular distribution parameter β2XA(ω) across the electronic resonances., 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.

The recent availability of intense and ultrashort extreme ultraviolet sources opens the possibility to investigate ultrafast electronic relaxation processes in matter in an unprecedented regime. In this work we report on the observation of two-photon excitation of interatomic Coulombic decay (ICD) in neon dimers using the tunable intense pulses delivered by the free electron laser FERMI@Elettra. The unique characteristics of FERMI (narrow bandwidth, spectral stability, and tunability) allow one to resonantly excite specific ionization pathways and to observe a clear signature of the ICD mechanism in the ratio of the ion yield created by Coulomb explosion. The present experimental results are explained by \emph{ab initio} electronic structure and nuclear dynamics calculations.