A very important characteristic in the chemistry of molecules interesting for planetary ionospheres is that they interact with the electromagnetic waves: γ, X rays and ultraviolet (UV) light. The dissociative double photoionization processes induced by VUV and EUV photons leading to the production of fragment ions with a high kinetic energy content could give in general an important contribution to the ion species escape from the atmosphere of some planets of the Solar System, like Venus, Mars and Titan. In fact, these processes occur via formation of intermediate molecular dications that can dissociate by Coulomb explosion towards the formations of two ion fragments having a kinetic energy released (KER) of several eV, and therefore much larger than the limiting thermal escape velocity. When CO2, C2H2 and N2O molecules are ionized using photons with an energy in the range of 30 to 65 eV, molecular fragmentation can be induced, with several two-body dissociation reactions leading to ion final products with high kinetic energy content [1,2]. These ionic species (CO+, O+, N2+, N+, NO+, H+, C+, CH+, CH2+ and C2H+) are formed by Coulomb explosion of an intermediate molecular dication (CO22+, N2O2+ and C2H22+, respectively). The fragments are characterized by a translational energy ranging between 1.0 and 5.5 eV (only for H+, the measured KER reaches the maximum value of 6.0 eV), which is large enough to allow some of them to escape from the atmospheres of Mars and Titan. In the case of O+, we can conclude that the dissociative double photoionization of CO2 induced by VUV and EUV photons in the ionosphere of Mars can contribute to explain the observed behavior of the O+ ion density profile measured by the Viking 1 lander in the upper atmosphere of this planet, compared with the CO22+ density profile as calculated for the Viking 1 lander and Mariner 6 spacecraft geophysical conditions.
CO22+, N2O2+, C2H22+ molecular dications formation and their Coulomb explosion with subsequent fragment ions escaping from planetary atmospheres
FALCINELLI, Stefano;ROSI, Marzio;PIRANI, Fernando;VECCHIOCATTIVI, Franco
2015
Abstract
A very important characteristic in the chemistry of molecules interesting for planetary ionospheres is that they interact with the electromagnetic waves: γ, X rays and ultraviolet (UV) light. The dissociative double photoionization processes induced by VUV and EUV photons leading to the production of fragment ions with a high kinetic energy content could give in general an important contribution to the ion species escape from the atmosphere of some planets of the Solar System, like Venus, Mars and Titan. In fact, these processes occur via formation of intermediate molecular dications that can dissociate by Coulomb explosion towards the formations of two ion fragments having a kinetic energy released (KER) of several eV, and therefore much larger than the limiting thermal escape velocity. When CO2, C2H2 and N2O molecules are ionized using photons with an energy in the range of 30 to 65 eV, molecular fragmentation can be induced, with several two-body dissociation reactions leading to ion final products with high kinetic energy content [1,2]. These ionic species (CO+, O+, N2+, N+, NO+, H+, C+, CH+, CH2+ and C2H+) are formed by Coulomb explosion of an intermediate molecular dication (CO22+, N2O2+ and C2H22+, respectively). The fragments are characterized by a translational energy ranging between 1.0 and 5.5 eV (only for H+, the measured KER reaches the maximum value of 6.0 eV), which is large enough to allow some of them to escape from the atmospheres of Mars and Titan. In the case of O+, we can conclude that the dissociative double photoionization of CO2 induced by VUV and EUV photons in the ionosphere of Mars can contribute to explain the observed behavior of the O+ ion density profile measured by the Viking 1 lander in the upper atmosphere of this planet, compared with the CO22+ density profile as calculated for the Viking 1 lander and Mariner 6 spacecraft geophysical conditions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
