The Escape Probability of Some Ions from Mars and Titan Ionospheres

Molecular Dications in Planetary Atmospheric Escape

“…Such total KER distributions show: (i) for the deprotonation process (Reactions (8) and (9)), a maximum at about 4.3 eV with a full width at half maximum (FWHM) of about 60%; (ii) for the symmetric dissociation (Reaction (10)) a maximum at 5.2 eV with a FWHM of 44%; and (iii) for the proton transfer rearrangement process via formation of the intermediate vinylidene dication (Reaction (11)) a maximum in the KER distribution at 4.5 eV with a FWHM of about 28%. One interesting characteristic of such distributions is that the one referred to the deprotonation process leading to the formation of H + and C 2 H + ions shows bimodal behavior (see Figure 4a) originated by the two possible mechanisms contributing to this reaction: (i) a "slow" dissociation component, Reaction (8), more important at low photon energy (hν ≤ 35 eV) where C 2 H 2 2+ is formed mainly in its ground 3 ∑ − g electronic state with a measured lifetime of about 108 ns; and (ii) a "fast" dissociation component, Reaction (9), via formation of a "short-lived" C 2 H 2 2+ intermediate dication having a lifetime shorter than 50 ns and coming from the 3 Π u excited electronic state whose accessible Franck-Condon zone occurs at about 37 eV. This state, accordingly to the potential energy curves calculated by Thyssen et al [22], correlates to ground state C 2 H + and H + products along an entirely repulsive curve with an energy release of about 7-8 eV.…”

“…The presence of two different mechanisms for this process is confirmed by the quite broad FWHM value (~60%) of the related total KER distribution (see Figure 4b). In order to clarify the relative importance of the two mechanisms discussed above (see Reactions (8) and (9)), we are planning to extend our photoelectron-photoionphotoion coincidence and ion imaging study to a wider photon energy range. Finally, it has to be noted that the translational energy content of each H + , C + , CH + and CH2 + product ion is quite large, with an average value of 4.0, 2.5, 2.0 and 2.5 eV, respectively.…”

“…Furthermore, ionic species are extremely important in the upper atmosphere of planets, where they govern the chemistry of ionospheres [5,6]. In particular, the ionosphere chemistry of Titan has recently been revealed to be extremely active by the instruments on board Cassini [7,8]. Finally, molecular ions have also been detected in comet tails [9].…”

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

“…In particular, the ionosphere chemistry of Titan has recently been revealed to be extremely active by the instruments on board Cassini [6,7]. Finally, molecular ions have also been detected in comet tails [1].…”

The Escape of O^+ and CO^+ Ions from Mars and Titan Atmospheres by Coulomb Explosion of CO22+ Molecular Dications

“…Moreover, ions are extremely important in the upper atmosphere of planets, where they control the chemistry of ionospheres [6,7]. For example, the chemistry of the upper atmosphere of Titan has been detected to be extremely active by the instruments on board Cassini [8,9]. Finally, various simple ionic species, as for example H 2 O + , CO + , CN + , CO + , have also been detected in comet tails [10].…”