Formation of complex organic. molecules in space. Wolf D. Geppert EWASS, Turku July 2013

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1 Formation of complex organic molecules in space Wolf D. Geppert EWASS, Turku July 2013

2 Formation of biomolecules in primeval soup under an atmosphere containing CH 4, NH 3, H 2 Problems: optically active compounds produced as racemates synthesis of biomolecules severely hampered by presence of O 2. Urey-Miller experiment

3 Biomolecules from space? Several amino acids found in the Murchison meteorite enantiomeric excess (L-form) detected Problem: survival of biomolecules through star-forming phase doubtful (Ehrenfreund, 2006) But: Precursors might survive? Fragment of Murchison metorite Murchison Where were biomolecule precursors formed? Delivery from space? Atmospheric reactions on early Earth?

4 Chemical processes in the Interstellar medium Processes must be barrierless (exclude most terrestrial neutral proceses) Three-body-processes excluded in the gas phase (low density) Reactions fulfilling these criteria 1. Radical-neutral and atom -neutral processes 2. Surface reactions (increasing importance) 3. Ion processes

5 Ionic processes in space absence of barrier requested & no third body processes Ion - neutral reactions (e. g. radiative association) A B AB h Ion-electron reactions for molecules exclusively dissociative recombination (DR) AB e - A B Ion-ion reactions (mutual neutralisation) A B - C D Synthesis of interstellar molecules via ion reactions and DR: Cl H 2 HCl H HCl H 2 H 2 Cl H H 2 Cl e - HCl H

6 Ion trap experiment CH 3 H 2 O CH 3 OH 2 h Gerlich & coworkers 22-Pole Ion Trap Pulsed Valve H 2 O seeded in Xe Ion Deflector He buffer CH 3 CH 3 15±5 K Mass spectrometer Stagnation pressure: 365 mbar H 2 O partial pressure: 26mbar at 295 K H 2 O 7% Xe 93 % Instantaneouce densities: [H 2 O] = cm -3 [Xe] = cm -3 Effective temperature T eff = 50±30 K

7 CH 3 H 2 O two processes - radiative and ternary CH 3 H 2 O He CH 5 O He CH 3 H 2 O CH 5 O h CRESU K k * / cm 3 s Radiative k r Ternary k Luca et al [He] / cm -3

8 The CRYRING storage ring Steps during the experiment Formation of ions in source 2. Mass selection by bending magnet Injection via RFQ and acceleration 4. Merging with electron beam Schematic view of CRYRING 5. Detection of the neutral products

9 Cooled cathode Anode Ion Beam Bending magnets Bending magnets Neutral fragments Electron cooler

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

11 Intensity / counts Fragment energy spectrum 1.4x10 4 D 1.2x x10 4 C3D OD 8.0x x10 3 C4D O2D 4.0x x10 3 2D C2D O C5D, O3D CO4D CO3D CO5D 0.0 3D CD O4D CO2D Fragment kinetic energy / MeV

12 Formation of dimethyl ether CH 3 OH 2 CH 3 OH CH 3 O(H)CH 3 H 2 O CH 3 O(H)CH 3 e - CH 3 OCH 3 H Rate constant of methyl transfer measured to be cm 3 s -1 (Karpas and Meot-Ner 1989) DR rate of CD 3 O(D)CD 3 branching ratios CD 3 O(D)CD 3 e - C 2 D x O ad 2 bd (7 5%) CD x O CD y ad 2 bd } C 2 D x OD y ad 2 bd (49 14%) CD x CD y OD z ad 2 bd (44 11%) Even a branching ratio of 1.5 % of formation of CH 3 OCH 3 in DR production in star-forming regions (Garrod & Herbst 2006) New observational data yield that formation of dimethyl ether partly happens on grain surfaces (Bisschop et al. 2013)

13 Ethanol in star-forming regions Sagittarius B2 NGC 7538 Kippis! Minä kaiken juon minä elämäni Detected in hot, dense star-forming regions Correlation with methanol

14 Formation of ethanol C 2 H 5 H 2 O C 2 H 5 OH 2 h C 2 H 4 H 3 O C 2 H 5 OH 2 h C 2 H 5 OH 2 e - C 2 H 5 OH H Radiative association rate constants too low to explain ethanol formation (Herbst 1987) DR of C 2 H 5 OH 2 only leads to ethanol only in max 7 % (rest split into two fragments containing one and 2 heavy atoms) Interstellar ethanol very probably formed on grain surfaces (Bisschop et al 2007): CH 3 CHO 2H C 2 H 5 OH

15 W 51 Formic acid Found in hot molecular cores (Sgr B2, Orion KL, W51) and dark clods (L134N) Formation of HCOOH by two processes invoked: HCO H 2 O HCO(H)OH h (1) O 2 CH 4 HCO(H)OH H (2) But: Process (2) leads to CH 2 OOH! (Van Doren et al. 2006) Removal little influence on model calculations

16 Formic acid Conservation of the heavy atom bonds in the DR of HCOOH 2 only in max 13 % of the events Furthermore: 7 other channels conserving COO structure: HCO(H)OH e - HCOOH H e. g. HCO(H)OH e - HCOO 2H Formic acid also probably formed on grain surfaces (Garrod & Herbst 2006) HCO OH HCOOH

17 Model calculations of HCOOH abundance Fractional abundance with respect to H 2 1x10-8 1x10-9 1x x x x x x x x10-17 Observations (Ohishi 1992) Old branching ratio New branching ratio Time / years Model calculation of HCOOH abundance in TMC-1 (UMIST code) In models of L134N no improvement

18 Titan s atmosphere 147 kpa surface pressure 94 % N 2, 6 % CH 4 Ar could resemble atmosphere of early Earth Traces of hydrocarbons and nitrogen compounds mixing extending to higher altitudes Dominant molecule Titan Earth N 2 N 2 Tropopause 35 km 8-18 km Homopause 1195 km 85 km IR (above) and visible (below) picture of Titan

19 Models of Titan s ionosphere Old models: mostly protonated hydrocarbons formed N N N

20 Ion-Neutral Mass Spectrometer (INMS) on board of Cassini 2 operating modes: a) open source mode for ions b) closed source for neutrals

21 INMS results in open mode Vuitton et al HCNH C 2 H C 3 H 5 5 C3 H HC 3 NH 3 CH 2 NH CH 2 3 CNH C 2 H 3 CNH N NH 4 C 2 H 5 CN H Blue line = fit without including new ions Red line = fit including new species, black dots data from Cassini

22 Nitrile formation: Acetonitrile (CH 3 CN) 2 pathways of synthesis conceivable: 1. C 2 H 4 N( 2 D) CH 3 CN H other products Abundance of N( 2 D) unclear Problem: Only 0.8 % CH 3 CN production (Balucani et al. 2004) But: other products can isomerise to CH 3 CN 2. CH 3 HCN CH 3 CNH CH 3 CNH e - CH 3 CN H Product branching ratio?

23 Nitriles in atmospheres Rich nitrile chemistry in N 2 /CH 4 atmospheres, first step to biomolecules can polymerise (e. g. with HCN) to tholines (aerosol and haze formation): NH R Titan s haze layer nrcn nhcn C N Tholine C n Destroyed by sequence protonation dissociative recombination? RCN C 2 H 5 RCNH C 2 H 4 RCNH e - RCN H other products? Tholine from the lab

24 Example: Acetonitrile (CH 3 CNH ) CH 3 HCN CH 3 CNH CH 3 CNH e - CH 3 CN H Dissociative recombination retains carbon chain in 65 % of cases Problem: radiative recombination mainly leads to CH 3 NCH collisional rearrangement with third bodies (Anicich 1994)

25 Dissociative recombination of protonated nitriles Ion Rate constant / cm 3 s -1 Probability of retention of carbon-nitrogen chain CH 3 CNH (T/300) % 35 % C 2 H 3 CNH (T/300) % 50% HCCCNH (T/300) % 72 % Probability of break-up of one C- C or C-N bond In C 2 H 3 CNH and C 2 H 3 CNH mostly central C-C bond broken Dissociative recombinations of protonated nitriles partly recycles nitriles lost through protonation Other reactive fragments also formed Reactions possibly important for exoplanets and early Earth

26 Conclusions on early Earth s atmosphere In Urey-Miller experiment amino acids formed in liquid tholines also generated lead to amino acids upon hydrolysis feasible process on early Earth? happening on exoplanet? H 2 O Nucleobases, amino acids, amino nucleobases acids

27 Conclusions Ion reactions are important processes in the chemistry of the interstellar medium and planetary atmospheres Synthesis pathways in the interstellar medium involving ion reactions often turned out as dead ends Molecular data on many ion reactions still lacking New experimental facilities (electrostatic storage rings, magnetoelectodynamic traps, ion traps) will enable research into these processes Review: Ion Chemistry in Space (gas phase) Larsson, Geppert & Nyman, Rep. Prog. Phys. 75, 6,

28 Acknowledgments The Scientific Committee for the invitation My colleagues at Stockholm University: M. Hamberg, E. Vigren, R. D. Thomas, V. Zhaunerchyk, M. Larsson.. The CRYRING team at Manne Siegbahn Laboratory: A. Källberg, A. Simonsson, A. Paál... The QUB Molecular Astrophysics team T. J. Millar, H. Roberts, C. Walsh.