Double Photoionization of Simple Molecules of Astrochemical Interest

Abstract

An experimental and computational investigation characterizing the processes following the double photoionization of the methyloxirane and N-methylformamide molecules has been reported. The double photoionization experiments have been performed at the Elettra Synchrotron Facility of Trieste (Italy). Preliminary data show: (i) in the case of methyloxirane, six different two-body fragmentation processes leading to ${\text{CH}}_{2}^{ + } /{\text{C}}_{2} {\text{H}}_{4} {\text{O}}^{ + } ,{\text{CH}}_{3}^{ + } /{\text{C}}_{ 2} {\text{H}}_{ 3} {\text{O}}^{ + } ,{\text{O}}^{ + } /{\text{C}}_{ 3} {\text{H}}_{6}^{ + } , {\text{ OH}}^{ + } / {\text{C}}_{ 3} {\text{H}}_{5}^{ + } ,{\text{C}}_{ 2} {\text{H}}_{3}^{ + } /{\text{CH}}_{ 3} {\text{O}}^{ + } ,{\text{C}}_{ 2} {\text{H}}_{4}^{ + } /{\text{CH}}_{ 2} {\text{O}}^{ + }$ pairs of final ions; (ii) in the case of N-methylformamide, two main two-body fragmentation processes, leading to ${\text{CH}}_{3}^{ + } + {\text{CH}}_{2} {\text{NO}}^{ + }$ and ${\text{H}}^{ + } + {\text{C}}_{2} {\text{H}}_{4} {\text{NO}}^{ + }$. The threshold’s energy for each dissociation channel is determined with the relative cross sections as a function of the investigated photon energy range. A careful analysis of recorded electron-ion-ion coincidence spectra mainly based on a Monte Carlo trajectory simulation is able to provide also the kinetic energy released (KER) distribution for the final ions of the investigated fragmentation reactions. These important experimental data are mandatory information to unravel the physical chemistry of the elementary processes induced by the interaction of photons, with simple relevant organic molecules: (i) the methyloxirane of astrochemical interest, being the first chiral molecule recently discovered in interstellar cloud Sagittarius B2; (ii) the N-methylformamide, being an important simple molecule containing the peptide bond, recently detected in the interstellar medium, in order to investigate its selective cleavage induced by UV photons. In the latter case, this can improve a deeper definition of formation/destruction routes in astrochemical environments of the more abundant formamide molecule.