Angular Distribution of Ion Products in the Double Photoionization of Propylene Oxide

Abstract

A photoelectron-photoion-photoion coincidence technique, using an ion imaging detector and tunable synchrotron radiation in the 18.0–37.0 eV photon energy range, inducing the ejection of molecular valence electrons, has been applied to study the double ionization of the propylene oxide, a simple prototype chiral molecule. The experiment performed at the Elettra Synchrotron Facility (Trieste, Italy) allowed to determine angular distributions for ions produced by the two-body dissociation reactions following the Coulomb explosion of the intermediate (C3H6O)2+ molecular dication. The analysis of the coincidence spectra recorded at different photon energies was done in order to determine the dependence of the β anisotropy parameter on the photon energy for the investigated two-body fragmentation channels. In particular, the reaction leading to CH3+ + C2H3O+ appears to be characterized by an increase of β, from β ≈ 0.00 up to β = 0.59, as the photon energy increases from 29.7 to 37.0 eV, respectively. This new observation confirms that the dissociation channel producing CH3+ and C2H3O+ final ions can occur with two different microscopic mechanisms as already indicated by the bimodality obtained in the kinetic energy released (KER) distributions as a function of the photon energy in a recent study. Energetic considerations suggest that experimental data are compatible with the formation of two different stable isomers of C2H3O+: acetyl and oxiranyl cations. These new experimental data are inherently relevant and are mandatory information for further experimental and theoretical investigations involving oriented chiral molecules and linearly or circularly polarized radiation. This work is in progress in our laboratory.

Strong-field ionization of CH3Cl: proton migration and association

“…However, the FWHM value of the KER distribution for the CH 2 + + HCl + pathway is reduced with increasing chirp. A broad KER distribution suggests the contribution of multiple excited electronic states 69 in a dissociation pathway. Therefore, some of the electronic states participating in the case of unchirped pulses are suppressed with increased positive chirps.…”

Production and Characterization of Molecular Dications: Experimental and Theoretical Efforts

“…By this technique, we were able to produce and characterize several molecular dications such a CO 2 2+ [ 77 , 78 ], N 2 O 2+ [ 79 , 80 ], C 6 H 6 2+ [ 81 , 82 ], and C 2 H 2 2+ [ 83 , 84 ], and more recently C 3 H 6 O 2+ [ 85 , 86 ], C 2 H 5 NO 2+ [ 87 ] (the dications of methyloxirane and N-methylformamide, respectively), pointing out their important role in the upper atmosphere of planets of the Solar system. In all cases, we performed double photoionization experiments using the tunable linearly polarized synchrotron radiation (with photon energy resolution of about 1.5 meV) as it is available at the GasPhase and CiPo beamlines of Elettra measuring: (i) the threshold energy for the different open fragmentation channels; (ii) the relative cross sections; (iii) the KER distribution of fragment ions at different photon energies; (iv) the angular distributions of fragment final ions with the relative anisotropy parameter β [ 75 , 76 ].…”

Experimental and Theoretical Study on Electron Ionization and Fragmentation of Propylene Oxide─the First Chiral Molecule Detected in the Interstellar Medium

“…In addition to these studies, Lifshitz et al and Turecek and McLafferty used 13 C and 2 H, respectively, to study in detail the fragmentation mechanism for CH 3 loss from the propylene oxide cation, showing that at the threshold, this process is dominated by loss of the epoxy methylene after hydrogen transfer from the terminal methyl group rather than direct methyl loss. In recent years, attention has also been given to the fragmentation of doubly charged propylene oxide ions, using photoelectron–photoion–photoion coincidence and imaging techniques to study the respective fragmentation dynamics. − …”