Angular Distributions of Fragment Ions Produced by Coulomb Explosion of Simple Molecular Dications of Astrochemical Interest

The double photoionization of N2O and C2H2 molecules by linearly polarized light in the 30-50 eV energy range has been studied by coupling ion imaging and electron-ion-ion coincidence techniques. In the case of N2O, for the two possible dissociative processes leading to N++NO+ and O++N2+, anisotropic angular distributions of ionic fragments have been measured, indicating that N2O ionizes when its axis is parallel to the light polarization vector and the fragments are separating in a time shorter than the dication rotational period. In the case of C2H2, the two-body dissociation reactions producing C2H++H+ and CH2++C+ have shown almost isotropic angular distributions, indicating the double photoionization occurs when acetylene is mainly oriented perpendicularly to the light polarization vector. The analysis of results based on a Monte Carlo trajectory simulation provides: i) the metastable N2O2+ and C2H22+ dication lifetimes, ii) the kinetic energy release (KER) distribution for the final ions resulting from the Coulomb explosion, and iii) the anisotropy β parameter values as a function of the investigated photon energy extracted from the measured ionic angular distributions.