Double photoionization of allene molecules by synchrotron radiation

Ionic species are of great interest in astrochemistry and in planetary atmospheres, and they can be formed in space in various way, such as by chemi-ionization and photoionization. In particular, the formation of doubly charged molecular species, which are called molecular dications, is of extreme interest since they were predicted to exist in the ionospheres of Mars, Venus and Titan, and then considerable amounts have been detected in such environments highlighting their relevant role, as for example, in the ion escape process from the atmosphere of Mars and Titan. In this specific work it is presented a summarizing description of the collection and computational analysis of the relevant data recorded following a double photoionization experiment on molecular species of interest in astrochemistry. In particular, the computational procedure used to analyze experimental data collected in the double photoionization of allene (C3H4) molecules by tunable radiation in the 25.0-45.0 eV photon energy range of the GASPHASE and CiPo beamlines of the ELETTRA synchrotron facility of Basovizza (Trieste, Italy) is outlined and discussed. Allene is the first member of the cumulene series CnH4, although it hasn’t been detected in the interstellar medium yet due to the lack of a dipole moment, it is well known for its axial chirality properties and its ground state electronic structure, which is of special interest due to its HOMO level being doubly degenerate. Data presented has been recorded in three different beamtimes using the ARPES (Angle Resolved PhotoEmission Spectroscopy) end station, which is an apparatus previously employed by our group in several experiments. It consists of a molecular beam apparatus coupled with a PEPIPICO (Photoelectron-Photoion- Photoion Coincidence) technique and TOF (Time-of-Flight) mass spectrometry, designed to measure the spatial momentum components of product fragment ions in the double photoionization experiments.