Fragmentation Dynamics of Astrochemical Molecules Induced by UV and EUV Photons

The present paper reports on an experimental and computational study aimed at characterizing the microscopic fragmentation dynamics of molecules in space that are subject to double photoionization phenomena by UV and EUV (Extreme Ultraviolet) photons. This kind of processes happening in planetary ionospheres and interstellar medium are simulated at the GASPHASE and CIRCULAR POLARIZATION beamlines of the ELETTRA Synchrotron Facility of Basovizza, Trieste (Italy) using the ARPES (Angle Resolved PhotoEmission Spectroscopy) end station: a molecular beam apparatus coupled with the PEPIPICO (Photoelectron-Photoion-Photoion Coincidence) technique and the TOF (Time-of-Flight) mass spectrometry. The used synchrotron radiation is in the 25.0–45.0 eV photon energy range. Preliminary data are presented for the case of the double photoionization of allene molecules whose photoinduced decomposition highlights 8 different open two-body fragmentation channels and 3 three-body dissociations. For each investigated dissociation channels threshold energies, relative cross sections and the appearing energy for the allene (C3H4)2+ dication as a function of the photon energy have been measured. Based on a Monte Carlo trajectory simulation, the computational analysis of the PEPIPICO spectra experimentally collected which is still in progress allows the possible extraction of the kinetic energy released (KER) and the angular distributions for the final fragment ions. These observables are very important to rationalize the physical chemistry of the elementary processes induced by the interaction between molecules and ionizing radiations in space.