Dissociative Recombination - a Key Process in Ionospheres of Giant Planets and their Satellites

Details Dissociative Recombination - a Key Process in Ionospheres of Giant Planets and their Satellites Dissociative Recombination - a Key Process in Ionospheres of Giant Planets and their Satellites

Aug 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007epsc.conf..613g&link_type=abstract

European Planetary Science Congress 2007, Proceedings of a conference held 20-24 August, 2007 in Potsdam, Germany. Online at ht

Other

Scientific paper

Ion reactions are amongst the most crucial processes in upper layers of planetary atmospheres. Dissociative recombination (DR) plays a particularly important role, since it usually is a barier-less process and thus feasible at the low collision energies prevalent in colder plasmas like the ones encountered in planetary ionospheres. Because of this fact it constitutes the only destruction mechanism for some ionospheric ions. DR processes are therefore included in model calculation of reaction networks for such environments, which greatly depend on the quality of the input data. Unfortunately, very often experimental results on these reactions are lacking even for the most important species. This is aggravated by the fact that, due to their exoergicity, DR reactions usually can have several pathways leading to very different products and the relative importance of these channels has often proven quite surprising. The CRYRING ion storage ring, located at the Manne Siegbahn laboratory at Stockholm University, allows measurement of DR branching ratios and cross sections at collision energies relevant to planetary ionospheres. We present such data for two different ions that are crucial for the chemistry of Io's and Titan's atmosphere, respectively: SO+2 and CH3CNH+. The DR of the SO+2 ion deserves special attention since it has been detected in both the exosphere and ionosphere of the Jovian satellite Io, by both the Voyager and Galileo missions (Bridge et al., 1979, Blanco-Cano et al., 2001). Io is especially interesting in this respect since its atmosphere is actually dominated by sulfur dioxide and, consequently, its ionosphere is particularly rich in SO+2 ions. The branching ratio of the S18O+2 + e- ! S18O + 18O channel amounts to 61%, whilst the three body breakup S18O+2 + e- ! S + 218O accounts for the remaining 39 % of the total reaction (the 18O isotopomere was used for experimental reasons in the present study). The thermal reaction rate obtained followed the expression k(T) = 4.6 ± 0.2 × 10-7 (T/300)-0.52±0.02 cm3s-1. Protonated acetonitrile (CH3CNH+) might play a pivotal role in the ionosphere of Titan since a strong signal with m/z= 42 was detected in the upper by the Ion Neutral Mass Spectrometer (INMS) on board the Cassini spacecraft during a flyby on 2005 April 16. Due to the chemistry prevailing in the atmosphere of Titan there seems to be little doubt that this signal should be attributed to CH3CNH+ (Vuitton, Yelle & Anicich 2006). In the case of CH3CNH+ 65% of the DR events resulted into retention of the bonds between heavy atoms, whereas the remaining 35% lead to breakage of one of these bonds. From the cross section a thermal rate coefficient of k(T) = 8.1 × 10-7 (T/300)-0.69 cm3s-1 was deduced. The impact of these findings on the chemistry of ionospheres of Io and Titan will be discussed. For the former celestial body, removal of photoelectrons by DR of SO+2 has been regarded as a possible reason for the fainting of FUV emissions during eclipses (Clarke et al. 1994). In the case of Titan it will be elaborated how the rates and branching ratios of the DR of CH3CNH+ and other nitrogen-containing ions could help to explain the abundance of these species detected by the Cassini-Huygens mission (which was much higher than the one expected by previous models). References X. Blanco-Cano, C. T. Russell, R. J. Strangeway, M. G Kivelson, Bulletin of the American Astronomical Society, 33,1084 (2001) H. S. Bridge et al., Science, 204, 987 (1979) J. T. Clarke, J. Ajello, J. Luhmann, N. Schneider, I. Kanik, J. Geophys. Res. 99, E4 8387 (1994) V. Vuitton, R. V. Yelle, V. G. Anicich, Astrophys. J. Lett. 647, 175 (2006)

Affiliated with

Also associated with

No associations

Rating

Dissociative Recombination - a Key Process in Ionospheres of Giant Planets and their Satellites does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Dissociative Recombination - a Key Process in Ionospheres of Giant Planets and their Satellites, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dissociative Recombination - a Key Process in Ionospheres of Giant Planets and their Satellites will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-971856