Kinetic Energy Release in molecular dications fragmentation after VUV and EUV ionization and escape from planetary atmospheres

Abstract

The measurements of the Kinetic Energy Release (KER) for various ionic species originating from two-body dissociations reactions, induced by double photoionization of CO2, C2H2 and N2O neutral molecular precursors of interest in planetary atmospheres, are reported. The KER distributions as a function of the ultraviolet (UV) photon energy in the range of 30–65eV (Vacuum and Extreme UV photons) are extracted from the electron–ion–ion coincidence spectra obtained by using tunable synchrotron radiation coupled with ion imaging techniques. This experimental method allows assessing the probability of escape for some simple ionic species in the upper atmosphere of Mars and Titan. In fact, the KER measured for H+, C+, CH+, CH2+, N+, O+, CO+, N2+ and NO+ fragment ions are ranging between 1.0 and 5.5eV (only for H+ the maximum value reaches 6.0eV), and these translational energies are large enough to allow these ionic species in participating in the atmospheric escape from Mars and Titan into space (for CO+, N2+ and NO+, the measured KER of 0.5–2.5eV, 0.5–2.8eV and 1.0–2.5eV, respectively, allows the possible escape only from the Titan atmosphere).