Laboratory measurements for ion chemistry in Titan's ionosphere. Odile Dutuit*,.
Véronique Vuitton and Roland Thissen. Institut de Planétologie et ...
Laboratory measurements for ion chemistry in Titan’s ionosphere Odile Dutuit*, Véronique Vuitton and Roland Thissen Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), France *Space Research Institute, Austrian Academy of Sciences, Graz, Austria
Models before Cassini measurements N2 H+ CH4
CH4+
CxHyNH+
CH5+
Cx H y +
C4H3+ N2 +
N2
N+
CH3+
HCNH+
C2 H 5 +
CH2+
C2H3+
HCN+
C2H4+ C3H3+
C6H7+ C4H5+
C6 H 5 + C4H7+
C3 H 5 + C5H5+
C4H5NH
C5H7+ Black = CH4 Red = C2H2 Blue = C2H4 Turquoise = HCN Plum = H2 Orange = hv, e Green = proton transfer
¾ Some unidentified peaks!
C7 H 7 +
+
Reaction rate key 1e-1 1e-2 1e-3
¾ Kinetic model with about 1250 chemical reactions (available from V. Anicich data base + some more)
CxHy + H+ odd mass CxHyN + H+ even mass
PROBLEMS !
Vuitton et al., Icarus 2007
INMS Model Vuitton et al., sous presse
Vuitton et al., Ap. J. 2006 42 CH3CN
NH3
18
CH2NH
30
C2H3CN C2H5CN
Missing peaks have been assigned to protonated ammonia and nitriles
54
56
Comparison between the INMS data and the model with uncertainties propagation N. Carrasco, P. Pernot, PSS 2007 INMS Model
Present databases… V. Anicich (2003) ~600 ion molecule reactions ion mass increases
CNC+ + C2H6 ==> C2H5+ +X CNC+ + C2H6 ==> C3H3+ + H2 HCN CNC+ + C2H6 ==> C3H5+ + HCN CNC+ + C2H6 ==> CxHyNz+ + C2H4 CNC+ + C4H2 ==> CxHyNz+ + HCN CNC+ + C4H2 ==> C4H2+ +X CNC+ + C4H2 ==> CxHyNz+ + CNC+ + H2O ==> CxHyNz+ + X CNC+ + H2O ==> HCO+ + HCN CNC+ + CH3CN ==> C2H3+ + C2N2 CNC+ + HC3N ==> C3H+ + C2N2 CCN+ + H2 ==> HCNH+ +H CCN+ + H2 ==> CxHyNz+ + CCN+ + CH4 ==> C2H3+ + HCN CCN+ + CH4 ==> HCNH+ + C2H2 CCN+ + CH4 ==> CHCCNH+ + H2 CCN+ + C2H2 ==> C3H+ + HCN CCN+ + C2H2 ==> HCNH+ +X CCN+ + H2O ==> HCNH+ + CO CCN+ + H2O ==> HCO+ + HCN CHCCN+ + H2 ==> C2H2+ + HCN CHCCN+ + H2 ==> CHCCNH+ + H CHCCN+ + CH4 ==> C3H4+ + HCN CHCCN+ + CH4 ==> CxHyNz+ + C2H2 CHCCN+ + CH4 ==> CHCCNH+ + CH3 CHCCN+ + C2H2 ==> C2H2+ + HC3N CHCCN+ + C2H2 ==> C4H2+ + HCN CHCCN+ + C2H4 ==> C2H4+ + HC3N CHCCN+ + C2H4 ==> CHCCNH+ + X CHCCN+ + C4H2 ==> C4H2+ + HC3N CHCCN+ + H2O ==> CHCCNH+ + X CHCCN+ + HC3N ==> HC5N+ + HCN CHCCN+ + HC3N ==> CxHyNz+ + H CHCCN+ + HC3N ==> CxHyNz+ + CHCCNH+ + C2H4 ==> CxHyNz+ + H HC5N+ + C2H4 ==> CxHyNz+ + X HC5N+ + C2H4 ==> CxHyNz+ + H2 HC5N+ + C2H4 ==> CxHyNz+ +
1.20E-009 1.20E-009 1.20E-009 1.20E-009 1.30E-009 1.30E-009 1.30E-009 7.00E-011 7.00E-011 4.10E-009 3.30E-009 9.00E-010 9.00E-010 7.00E-010 7.00E-010 7.00E-010 1.60E-009 1.60E-009 1.60E-009 1.60E-009 4.45E-012 4.45E-012 5.90E-010 5.90E-010 5.90E-010 6.40E-010 6.40E-010 6.70E-010 6.70E-010 8.90E-010 6.70E-010 1.30E-009 1.30E-009 1.30E-009 1.30E-009 1.20E-009 1.20E-009 1.20E-009
Measurements at 300K
Many measurements with deuterated samples No description of ion structures
Few reaction pathways are exhaustively described
Almost no information on reactions of molecular ions containing nitrogen CxHyNz+
Are refinements on reactions needed? • Ion-molecule reactions of the model: A+ + B → C+ + D • Rate constants
NO! (with exceptions)
• Product branching ratio (% of products):
YES!
• Ion-electron recombination reactions: YES! A+ + e → neutral products For reactions with bigger species CxHyNz+, strong need for more laboratory work!
Differential reactivity of C3H3+ isomers
• Linear C3H3+ ions are reactive in red, distinction of isomers in black, no distinction
Carrasco et al, PSS 2008
C3H3+
Density (cm-3)
• Cyclic C3H3+ ions are non reactive,
C5H5+ C5H7+
m/z (amu)
The case of the ion-electron recombination reactions Very scarce experimental measurements on the products of A+ + e reactions No simple theoretical model to make predictions works! Experimental studies are very hard to do! Hypothesis made in models: loss of H or H2, but the few known cases show that dissociative recombination is very often very important … ex: C3NH4+ + e → C3NHx + y H + z H2 50% → C2Hx + CNHy + z H + w H2 49% → others 1% Vigren et al., Ap. J. 2009
Products from ion-molecule reactions are hard to predict! They need to be measured… C3H3+ + C6H6 (benzene) → C6H6.C3H3+ association → C6H7+ + C3H2 proton transfer C3H3+ + C7H8 (toluene) → C7H8.C3H3+ association → C9H7+ + CH4 reaction → C10H9+ + H2 reaction → C10H8+ + H2 + H reaction →no proton transfer Adams et al. Faraday Disc. 2010
84% 16% 43% 28% 17% 12%
Recent discovery: complex negative ion chemistry in Titan ionosphere C3N-/C4HCN-
Modelling shows that ¾ CN- produced mainly by HCN + e ÆCN- + H ¾ C3N- produced mainly 1027-1200 km by CN- + HC3N Æ C3N+ HCN 1200-1400 km
m/z (amu)
CAPS measurements at ~1000 km
A. J. Coates et al., GRL 34, L22103 (2007)
but very few reactions 1400-1600 of negative ionskm have been measured! Vuitton et al., PSS 2009
KIDA (Kinetic Database for Astrophysics) Coordinated by V. Wakelam (Lab. Astrophys. Bordeaux, France)
Data base with critical evaluation http://kida.obs.u-bordeaux1.fr Positive and negative ion-molecule reactions, as well as e-ion recombination reactions, still incomplete… Two working groups : - GRAMIS in France - ISSI Bern, Switzerland Funding by French Programs, ISSI, European Network “Europlanet RI” 2009-2012
Conclusions ¾ Existing data on positive ion molecule reactions with small species need only some refinements, in particular for N containing molecules ¾ Need for new laboratory measurements for “heavy” positive ion molecule reactions ¾ Need for experimental and theoretical data on ionelectron recombination reactions ¾ Need for new laboratory measurements for negative ion molecule reactions ¾ Importance of critical evaluation of literature data and help from chemists to make assumptions on unknown reactions
