The Fragmentation Dynamics of Simple Organic Molecules of Astrochemical Interest Interacting with VUV Photons

An experimental investigation on the fragmentation dynamics following the double photoionization of simple organic molecules of astrochemical interest, propylene oxide and N-methylformamide molecules, induced by VUV photons has been reported. Experiments used linearly polarized light in the 18-37 eV (propylene oxide) and 26-45 eV (N-methylformamide) photon energy range at the ELETTRA Synchrotron Facility of Trieste (Italy), coupling ion imaging and electron-ion-ion coincidence techniques with time-of-flight mass spectrometry. In the case of propylene oxide, six different two-body fragmentation processes have been recorded with the formation of CH2 +/C2H4O+, CH3 +/C2H3O+, O+/C3H6 +, OH+/C3H5 +, C2H3 +/CH3O+, C2H4 +/CH2O+ ion pairs. On the other hand, the double photoionization of N-methylformamide occurs producing two main fragmentation reactions, forming CH3 + + CH2NO+ and H+ + C2H4NO+. The relative cross sections and the threshold energies for all fragmentation channels are recorded as a function of the photon energy. Furthermore, 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 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. The obtained results are important to clarify the physical chemistry of the elementary processes induced by the interaction of ionizing radiations with simple organic molecules of astrochemical interest: propylene oxide and N-methylformamide.