Cosmic dust formation at cryogenic temperatures

1. Max-Planck-Institut für Astronomie Heidelberg Friedrich-Schiller- Universität Jena Cosmic dust formation at cryogenic temperatures Gaël Rouillé Laboratory Astrophysics and Cluster Physics Group G. Rouillé – 22 November 2013 – Taipei

2. Collaborators and Sponsors • Thomas Henning • Cornelia Jäger • Friedrich Huisken • Serge A. Krasnokutski • Svitlana Zhukovska (MPIA) • Melinda Krebsz (Eötvös Loránd University, Budapest) • Max Planck Institute for Astronomy (Heidelberg) • Friedrich Schiller University (Jena) • Deutsche Forschungsgemeinschaft (DFG): Priority Program 1573 "Physics of the Interstellar Medium" (ISM-SPP) G. Rouillé – 22 November 2013 – Taipei

3. Cosmic dust • Main components - amorphous silicates (e.g. Kemper et al. 2004, 2005) - carbonaceous grains • Formation - condensation in stellar envelopes and - growth in the interstellar medium (ISM) – in molecular clouds >Need for data on the formation of silicates at ISM temperatures (< 100 K) • Major form for interstellar Si in the gas phase (Herbst et al. 1989) - SiO ~0.001-0.1 per 106 H atoms >Experiments on the low-T condensation and accretion of SiO G. Rouillé – 22 November 2013 – Taipei

4. Laboratory methods for low-T condensation studies G. Rouillé – 22 November 2013 – Taipei

5. Helium droplet beam apparatus G. Rouillé – 22 November 2013 – Taipei

6. Mass spectroscopy Krasnokutski et al. (submitted) • Dopants - SiO - H2O • Smaller peaks - He clusters >Detection of SixOy compounds G. Rouillé – 22 November 2013 – Taipei

7. ion signal 0 Nmin N Reaction energies (1) • The evaporation of a single He atom requires 5 cm-1 equivalent energy • Determined using the minimum He droplet size Nmin that allow the detection of the reactants and products • Example E(SiO + SiO → Si2O2) ~ Nmin(detection of Si2O2) – 2 Nmin(detection of SiO) G. Rouillé – 22 November 2013 – Taipei

8. Reaction energies (2) Krasnokutski et al. (submitted) • Dopants - SiO - H2O • Ion count rate divided by the product of 3 probabilities - pick up of reactants - ionization of the droplets - transfer of charge from the droplets to their contents >Reaction energies SiO + SiO → Si2O +178 kJ mol-1 SiO + Si2O2 → Si3O3+291 kJ mol-1 • Results supported by theory G. Rouillé – 22 November 2013 – Taipei

9. Matrix isolation spectroscopy apparatus • UV/vis/IR absorption spectroscopy • Substrate: CaF2 or KBr • Laser source: pulsed Nd:YAG, 266 nm, 5 ns pulse duration, 10 Hz, 1.5-1.9 mJ per pulse G. Rouillé – 22 November 2013 – Taipei

10. Ne matrix at 6 K – UV • SiO A1Π ← X1Σ+ • Hormes et al. (1983) >Detection of isolated atoms, molecules, and small clusters G. Rouillé – 22 November 2013 – Taipei

11. Ne matrix at 6 K – FTIR • SiO target • 30 min deposition • Assignment Khanna et al. (1981) – N2 matrix, ≥ 30 K >SiOSi bands similar to SiO2 signature G. Rouillé – 22 November 2013 – Taipei

12. Ne matrix at 6 K – FTIR • SiO / MgO target • 60 min deposition >SiOSi bands similar to SiO2 signature G. Rouillé – 22 November 2013 – Taipei

13. SiO target 0.5 mm SiO target c130117 c131024 Condensates in SiO-doped Ne experiments G. Rouillé – 22 November 2013 – Taipei

14. SiO target SiO target c131024 c131024 Condensates in doped Ne experiments >TEM: fluffy morphology, amorphous, homogeneous structure >EDX: SiO target → SiO grains SiO/MgO target → Mg0.2SiO G. Rouillé – 22 November 2013 – Taipei

15. Summary and outlook • Aggregation in superfluid He nanodroplets at 0.37 K >No energy barrier to the reactions SiO + SiO → Si2O2+ 178 kJ mol-1 SiO + Si2O2→ Si3O3+ 291 kJ mol-1 • Aggregation in Ne matrices at 6-13 K >SiO can form grains at T relevant to the ISM - micrometer scale - amorphous structure like interstellar silicates - homogeneous structure - mid-IR SiOSi features similar to SiO2 - co-deposited Mg atoms can be included into condensing SiO grains • Next steps - condensation with more Mg and O, with Fe → silicate targets – with UV exposure - addition of C - deposition on substrates relevant to astrophysics(e.g. silicates) G. Rouillé – 22 November 2013 – Taipei