More than a dozen ions hitherto identified in the interstellar medium.

1. Interstellar ion chemistry More than a dozen ions hitherto identified in the interstellar medium. Interstellar chemistry once thought to be dominated by ion chemistry. Ions found in interstellar clouds, shock waves, ionospheres, etc. The “Horsehead nebula” (Ori) Aurora over Alaska The “Cat’s eye” (Draco)

2. Important ion reactions in the ISM • Ion - neutral reactions ( H2+ + H2 H3+ + H ) • Ion - electron reactions ( H3+ + e- 3 H ) • Ion - ion reactions (H- + H+ 2 H ) (quite unexplored)

3. Feasible pathway of molecule synthesis in space Cosmic Ray Ionization Ion-Molecule Reactions Recombination For example: Presumed synthesis of methanol 1.Ion-molecule reaction 2.Dissociative recombination CH3+ + H2O  CH3OH2+ CH3OH2+ + e- CH3OH + H

4. Radiative association Scheme of a radiative association Redissociation in competition with radiating off of energy CH3+ + H2O  CH3OH2+ + hn

5. Important electron-ion reactions A+ + B- Resonant ion pair formation (high energies) AB+(v=m) + e- Elastic/inelastic/ superelastic (n=m/n<m/n>m) scattering AB+(v=n) + e- AB + hn Radiative recombination (too slow) A + B Dissociative recombination

6. Dissociative recombination (DR) in space Dissociative recombination (DR) in interstellar chemistry • Negative charge in the interstellar medium (ISM) thought to present mostly in the form of electrons. • DR often the final step of synthesis of neutral molecules in the ISM. (HX+ + e- X + H ) • Dissociative recombination(DR) often the only way to destroy cations. • Ample data on of DR rates, little on branching ratios. • Branching ratios often hard to explain by ”common sense”. • DR can lead to excited states that emit characteristic lines.

7. Problems to quantify DR reactions General rule:Conditions must match interstellar ones: • Ions have to be rotationally and vibrationally cool. • Three-body processes must be excluded. • Low relative translational energies of reactants. Additionally:Clear identification of the ion (isomeres) and products. Up to the 90’s measurements restricted to afterglow experiments.

8. Theoretical prediction of the pathways of DR reactions Bates’s theory 1986:Dissociative recombinatons favour the pathway(s) which involve(s) least orbital rearrangement, e. g.: N2H+ + e-N2+ H N2OH++ e-N2O+ H • Difficult to obtain reliable potential surfaces due to involvement of highly excited states very few high-level ab initio studies on DR reactions available

9. Flowing afterglow 4 steps: 1.Production of He+ by discharge in He: He+ e- He+ + 2 e- 2.Reaction of He+ with H2: He+ + H2 H2+ + He H2+ + H2 H3+ + H 3.Reaction of H3+ with other substances, e.g. CO: H3+ + CO  HCO+ + H2 4.Recombination of the ion: HCO+ +e- H + CO

10. Glosik et al. 2006

11. Advantages and disadvantages of flowing afterglow +Low operational costs. +Thermal equilibrium of reactants. + Detection of products by mass spectromtry. +Detection of electron degradation by Langmuir probe. -Impure reactants - except very simple systems like H3+. - Mearurements only at high (room) temperatures.

12. Storage ring (CRYRING) Steps during the experiment 1.Formation of the ions in the source 2.Mass selection by bending magnet 3. Injection via RFQ and acceleration 4. Merging with electron beam 5. Detection of the neutral products 3 2 1 4 5 Schematic view of CRYRING

13. Cooled cathode Anode Ion Beam Neutral fragments Bending magnets Bending magnets Electron cooler

14. e- GRID technique without grid Particle loss Surface barrier detector Signal without grid (all events lead to full mass signal) with grid Grid T=0.3 e- Branching ratio Signal with grid (mass spectrum dependent on branching ratio and T) Probability T(1-T)

15. Advantages and disadvantages of storage rings • Low (interstellar) relative kinetic energies of the reactants. • Mass selection of the ion produced. • All products can be identified. • Low background. • Only radiative cooling possible. • No straightforward identification of product internal states. • High set-up and operation costs.

16. N2H+ + e- One of the most prominent ions in dark interstellar clouds. N2 lost through protonation might be fully recovered by DR of N2H+: N2+ H3 N2H+ + H2 N2H+ + e-N2+ H Most of interstellar nitrogen thought to be stored as N2. Tracer for the unobservable N2. Present in Titan’s ionosphere. Saturn’s satellite Titan

17. HCO+ + e- HCO+ formed easily in the interstellar medium from CO through protonation (e. g. by H3+). One of the most important carbon- containing interstellar ions. Cameron bands in Red Rectangle maybe due to excited CO from DR of HCO+. Cameron bands in the Red Rectangle The ”Red Rectangle”

18. HCS+ + e- HCS+ is the most important sulfur-containing interstellar molecular ion. In dark clouds, a high HCS+/CS ratio is found. CS presumably formed by DR of HCS+. Very low rate of DR used in astrophysical models. How does the rate and branching ratio of the DR affect the HCS+/CS ratio ?

19. N2H+ + e- / HCO+ + e- HCO+ + e- reaction channels N2H+ + e- reaction channels HCO+ + e- H + CO (X 1S+) DH = - 7.45 eV H + CO (a 3P) DH = - 1.43 eV H + CO (a 3S+) DH = - 0.75 eV HC + O DH = + 0.17 eV OH + C DH = - 0.75 eV N2H+ + e- N2 + H DH = - 8.47 eV NH + N DH = -2.40 eV N2H+ fragment energy spectrum HCO+ fragment energy spectrum C+O O C+O+H C+H C O+H

20. Grid T=0.3 e- N2H+ + e- / HCO+ + e- Evaluation matrix N2H+ + e- reaction channels N2H+ + e- N2 + H DH = - 8.47 eV NH + N DH = -2.40 eV

21. Reaction channel Branching ratio N2 + H 0.36 N + NH 0.64 Evaluation of the branching ratios Evaluation matrix Branching ratios

22. k / cm3 mol-1s-1 Our data FALP* 1.00.110-7 (T/300)-0.510.02 1.7  10-7 (T/300)-0.90 N2H+ + e- Cross section of N2H+ + e- Dependence of s on relative kinetic energy Reaction rates of N2H+ + e- k(T) • Taken from: Smith, D., & Adams, N. G. 1984, ApJ, 284, L13

23. N2H+ + e- / HCO+ + e- Branching ratios } Reaction rates

24. N2H+ in prestellar cores Aikawa et al. 2005 R / au • HCO+ is depleted in the centre of the core, N2H+ is constant, NH3 slightly enhanced. • Explanation: CO frozen out, N2 isn´t.

25. BUT • Temperature desorption behaviour of N2 and CO differs only slightly. (Schlemmer and co-workers 2006) • No explanation for enhancement of ammonia near the core centre.

26. Explanation Taken from Aikawa et al. 2005 • Two destruction mechanisms for N2H+, only DR for HCO+: N2H+ + CO  HCO+ + N2 N2H+ + e-  Products • At low temperatures DR becomes the only degradation process (CO frozen out, but N2 also) • Formation of NH leads to enhancement of NH3.

27. Imaging analysis Can we gather information about the product kinetic energy ? PMP Trigger MCP e- Beam splitter v Phosphorus screen CCD camera

28. HCO+ + e- reaction channels HCO+ + e- H + CO (X 1S+) DH = - 7.45 eV H + CO (a 3P) DH = - 1.43 eV H + CO (a 3S+) DH = - 0.75 eV HC + O DH = + 0.17 eV OH + C DH = - 0.75 eV HCO+ + e- Reaction channels leading to differentelectronic energy levels of CO

29. Imaging of DCO+ Fit of the different electronic state contributions

30. Conclusions N2H+/ HCO+/ HCS+ In the DR of N2H+, the break-up of the N-N bond dominates. In the DR of HCO+, the CO + H channel is preeminent. Recombination of HCO+ partly leads to CO in the 3Pu state, which can explain the Cameron bands in the Red Rectangle. In the DR of HCS+, the break-up of the C-S bond is favoured. Reaction rate in the N2H+ andHCO+ DR reactions in agreement with previous FALP measurements.

31. New branching ratios in a model of TMC-1 *Ohishi, M. , Irvine, W. M. Kaifu, N., Astronomy of Cosmic Phenomena, 171

32. Conclusions from model calculations Abundances of N-containing compounds predicted better assuming an older age of TMC-1. Some improvements for molecule densities that proved difficult to model (H2O, HCOOH). No big influence on models of circumstellar envelopes, planetary nebulae and diffuse clouds.

33. SO2+ + e- Influence on interstellar sulfur chemistry. SO2 is found in atmospheres of planets (Venus) and satellites (Io). Important role of SO2+ in the ionosphere of Io. Three-body break-up energetically allowed. Iupiter´s moon Io

34. SO2+ + e- SO2+ + e- reaction channels SO2+ + e- SO + O DH = 6.32 eV S + O2 DH = 6.40 eV S + 2ODH = 1.22 eV Branching ratios of SO2+ + e- Reaction rate k(T) = 4.6  0.110-7 (T/300)-0.520.02 cm3 mol-1s-1

35. Consequences Decay of SO2+ in Io’s ionosphere during eclipse probably caused by DR. Strong observed UV lines of O(I) and S(I) could be due to increased S- and O-atom production by three-body break- up in DR. Possible role in the ionosphere of Venus ?

36. Methanol in space Responsible for maser emission in star-forming regions. Evolution indicator in star-forming regions Used for determination of kinetic temperature and H2 density simultaneously. From CH3OH2+/CH3OH ratio electron temperature in cometary coma derived. The Bear Claw Nebula, where a strong methanol maser was detected

37. Production of methanol in the ISM CH3+ + H2O  CH3OH2+ CH3OH2+ + e- CH3OH + H With a high rate of DR, the radiative association rate should be about 1.2  10-10 cm3s-1at 50 K. (Herbst et al. 1985)

38. But... Ion trap experiments yielded a an upper limit of 2  10-12 cm3s-1at dark cloud temperatures (Luca et al. 2002). a factor of 60 too low ! However... CH3+ not detected so far, densities only estimates from models. Uncertainties in water densities. If the DR of CH3OH2+ leads to methanol with a branching ratio of close to 100 %.......

39. Fragment energy spectrum of CD3OD2+

40. Fragment energy spectrum of CD3OD2+ CD3OD2+ + e-CD4 + OD CD2 + OD + D2 CD3 + D2 + O CD3 + D2O CDO+ 2D2 CDO+ D2 + 2D CO + 2D2 + D CO + D2 + 3D CD3OD2+ + e- CD3OD+ D CD3 + OD + D CD2 + D2O + D CD+ D2O + D2 CD3O+ 2D CD3O+ D2 CD2O+ D2 + D CD2O+3D CD4 + O + D Some of the channels deliver products with the same mass indistinguishable.

41. Branching ratios CD3OD2+/CH3OH2+

42. 2-,3- and 4-body processes

43. 2-,3- and 4-body processes Thermal reaction rate (CD3OD2+): k = 9.11  10-7 (T/300)-0.63 cm3s-1 s = 9.55  10-16 E(eV)-1.2cm2 For the undeuterated isotopomer (CH3OH2+): k = 8.91  10-7 (T/300)-0.59 cm3s-1 Cross-section vs. collision energy

44. Model Calculations Observed methanol density (TMC-1) CH3OH + H branching ratio = 1 CH3OH + H branching ratio = 0.06 UMIST (Rate99) model predictions for methanol density in TMC-1 Including new ratesfor theradiative associationof CH3+ and H2O, (Luca et al. 2002) thepeak methanolrelativeabundancesinks to7  10-13.

45. New UMIST model CH3OH + H branching ratio = 1 CH3OH + H branching ratio = 0.06 + new rate for CH3+ +H2O Observed methanol density (TMC-1) UMIST (Rate04) model predictions for methanol density in TMC-1 Main gas phase route to CH3OH is now CH3CHO+H3+ CH3OH + CH3+ k = 1.4  10-9cm3s-1 at 300K

46. Conclusions Three-body break-ups dominate. Production of CH3OH only 3 % (CD3OD only 6 %). No big isotope effects Gas-phase mechanism for interstellar methanol very unlikely. In line with the following facts: Formation of methanol on CO ice surfaces possible at 10 K. (Watanabe et al. 2004) • Models including grain surface desorption reproduce methanol densities (Herbst 2006)

47. Can we close the books ? • Anticorrelation of CO and CH3OH in dense clouds. (Buckle, 2006) • No experimental evidence for surface desorption of freshly formed methanol

48. DR of other CHxO+ systems Retention versus break-up of CO-bond  Increasing hydrogen saturation favours C-O bond rupture A rule for DR of hydrogen-containing ions ?

49. DR of (CD3)2OD+ • Similar mechanism to methanol postulated for dimethyl ether. • Similar problems ? CH3+ + CH3OH  (CH3)2OH+ (CH3)2OH+ + e- CH3OH + H

50. YES ! Production of (CD3)2O only 6 %) ! Grain surface process for formation of dimethyl ether unlikely (Ehrenfreund and co-workers, 2006) AND: