An experimental investigation on the fragmentation dynamics following the double photoionization of simple molecules of astrochemical interest, as carbon dioxide, propylene oxide and N-methylformamide, induced by VUV photons has been reported. Experiments used linearly polarized light in the 18-37 eV (propylene oxide), 26-45 eV (N-methylformamide) and 34-50 eV (carbon dioxide) photon energy range at the Elettra Synchrotron Facility of Trieste (Italy) [1-3]. Ion imaging and photoelectron-photoion-photoion (PEPIPICO) coincidence techniques are used with time-of-flight mass spectrometry (see Fig. 1) [4,5]. In the case of propylene oxide, six different two-body fragmentation processes has been recorded with the formation of CH2+/C2H4O+, CH3+/C2H3O+, O+/C3H6+, OH+/C3H5+, C2H3+/CH3O+, C2H4+/CH2O+ ion pairs. The double photoionization of N-methylformamide occurs producing two main fragmentation reactions, forming CH3++CH2NO+ and H++C2H4NO+, while carbon dioxide dissociates by Coulomb explosion of the intermediate (CO2)2+ dication into CO++O+ final ions. The relative cross sections and the threshold’s energy for all fragmentation channels are recorded as a function of the photon energy. In the case of the double photoionization of propylene oxide, the measure of the kinetic energy released distribution for the CH3+/C2H3O+ final ions with the their angular distributions allowed the identification of a bimodal behavior indicating the possible formation of two different stable isomers of C2H3O+: acetyl and oxiranyl cations. In the case of CO2, the production of CO+ and O+ fragments with a high kinetic energy content (2.0 and 3.8 eV, respectively) can explain the lack in the O+ expected concentration of the Mars atmosphere as measured by Viking 1 lander and Mariner 6 spacecraft . This energy is large enough in the case of Mars and Titan to allow these fragments to reach sufficient velocity to escape into space. Therefore this process can in principle contribute to the continuous erosion of these planetary atmospheres.
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