Cryochemistry in the inert and interstellar media

Transcription

1 Cryochemistry in the inert and interstellar media Serge A. Krasnokutski Friedrich Schiller University of Jena, Jena, Germany MPI for Astronomy, Königstuhl 17,69117 Heidelberg, Germany

2 Holes in heaven Herschel, W., Phil. Trans. 75, 213 (1785)

3

4 T = K

5 The Boomerang Nebula T = 1 K

6 Motivation k = A e -E a / RT T = 0.37 K T = K

7 Reaction of Al atoms with oxygen molecules Al + O 2 AlO + O J. Phys. Chem. A 101, 9988 (1997)

8 Reaction of Si atoms with oxygen molecules T = 0.37 K k > cm 3 mol -1 s Astron. Astrophys. 372, 1064 (2001) J. Phys. Chem. A 114, (2010)

9 Chemical models of reactions in the ISM Gas-phase or grain-surface reactions? Grain-surface reactions Gas-phase reactions A + B AB A + B C + D accretion desorption Grain hopping Grain-surface reactions can be affected by catalytic activity of the grain surface. However, the exact chemical composition of the cosmic dust grains is not known.

10 The matrix isolation scheme

11 The matrix isolation experimental setup

12 Formation of (SiO) n clusters in Ne matrix Astrophys. J. 782, 10pp (2014)

13 Formation of SiO bulk after evaporation of Ne matrix Astrophys. J. 782, 10pp (2014)

14 Formation of SiO bulk after evaporation of Ne matrix Astrophys. J. 782, 10pp (2014)

15 The He droplet experimental setup

16 The properties of helium nanodroplets The temperature of the He droplets is well known (T = 0.37 K). The He droplets are superfluid. Therefore, the mobility of the dopant species is not hindered. The liquid helium is the least polar solvent and interacts only weakly with dopant molecules. The use of He droplets allows few additional detection techniques.

17 The properties of helium nanodroplets P k z = (z)k k! exp ( z) Angew. Chem. 43, 2622 (2004).

18 Monitoring chemical reactions in He droplets 1. Calorimetry measurements 2. Observation of chemiluminescence n > Mass spectrometric detection 4. Laser spectroscopic detection < n < 50000

19 Reactions inside helium droplets 1) Large droplets n1 > ) Small droplets n1 < Product ejection Er = (n1 n2) 5 cm-1 d = 4.44 n1/3 Å

20 The determination of the mean sizes of He droplets Ion signal at He 2 mass (arb. units) Å 91 Å 100 Å 112 Å 130 Å Time ( s) To measure the average He droplet diameter Pressure in the detector chamber (10-9 mbar) To measure the average number of He atoms inside a He droplet Thousand He atoms per droplet

21 Calorimetry study of Al + O 2 reaction J. Phys. Chem. A, 115, 7120 (2011)

22 Calorimetry study of (SiO) n cluster formation Astrophys. J. 782, 10pp (2014)

23 Calorimetry study of (SiO) n cluster formation Astrophys. J. 782, 10pp (2014)

24 Detection of chemical reactions 1. Calorimetry measurements 2. Observation of chemiluminescence n > Mass spectrometric detection 4. Laser spectroscopic detection < n < 50000

25 Chemiluminescence study of Mg + O 2 reaction CL intensity (arb. units) n = 1 Light intensity (arb. unit) y = 0 mm y = 1 mm y = 2 mm y = 3 mm y = 4 mm y = 5 mm Probability (%) n = 2 n = 3 n = 4 n = Distance x (mm) n = p Mg (10-5 mbar) 1. CL results from electronically and vibrationally excited reaction products (Mg n O 2, n 2) which left the He droplets 2. A considerable time delay between chemical reaction and light emission was observed. It was found that the chemical reaction is unexpectedly fast and has a first-order reaction rate larger than s -1. J. Phys. Chem. A 114, 7292 (2010)

26 Detection of chemical reactions 1. Calorimetry measurements 2. Observation of chemiluminescence n > Mass spectrometric detection 4. Laser spectroscopic detection < n < 50000

27 Mass spectrometry study of Si + O 2 reaction Si only Si + O 2 ion signal SiO SiO 2 Si 2 O Si 2 O 2 Si 2 O mass (amu) J. Phys. Chem. A, 114, (2010)

28 Mass spectrometry study of Si + O 2 reaction O 2 O 4 O 5 Ion signal change (arb. units) He n Si SiO SiO 2 SiO 3 OH 2 O H O 2 2 SiOH O 2 SiO H O 2 2 SiOH Si 2 Si O 2 Si O 2 2 Si 3 T = 10 K (d He = 13 nm) Si O 2 3 Si Mass (amu) J. Phys. Chem. A, 114, (2010)

29 Detection of chemical reactions 1. Calorimetry measurements 2. Observation of chemiluminescence Laser spectroscopic detection n > Mass spectrometric detection 4. Laser spectroscopic detection n < Laser induce fluorescence (LIF) No mass selectivity Average sensitivity Works only for luminescent molecules Resonance two photons ionization (R2PI) Mass selectivity High sensitivity Works for most of the molecules

30 R2PI spectra of Fe atoms in the gas phase and solvated in helium droplets J. Phys. Chem. A 118, 2612 (2014)

31 Attenuation of iron R2PI signals J. Phys. Chem. A 118, 2612 (2014)

32 Formation of large clusters inside He droplets (SiO) n Si + H 2 O Cluster formation can be achieved by aggregation of separate cooled atoms or molecules, which is similar to the processes occurring in the interstellar space.

33 Formation of (SiO) n clusters inside He droplets Astrophys. J. 782, 10pp (2014)

34 Formation of SiO bulk after in He droplets Astrophys. J. 782, 10pp (2014)

35 Ultra-low-temperature reactions of atomic carbon with PAH Molecules 1) High abundance of PAH molecules is established T. Allain, E. Sedlmayr, and S. Leach, Astron. Astrophys. 323, 163 (1997). 2) PAHs are proposed to be responsible for the variety of interstellar features such as DIBs, UIBs, and the nm extinction bump. R. Ruiterkamp, T. Halasinski, F. Salama, B. H. Foing, L. J. Allamandola, W. Schmidt, and P. Ehrenfreund, Astron. Astrophys. 390, 1153 (2002). L. J. Allamandola, D. M. Hudgins, and S. A. Sandford, Astrophys. J. 511, L115 (1999). 3) The presence of only benzene (C 6 H 6 ) in the ISM is established. J. Cernicharo, A. M. Heras, A. G. G. M. Tielens, J. R. Pardo, F. Herpin, M. Guelin, and L. B. F. M. Waters, Astrophys. J. 546, L123 (2001).

36 Motivation Requirements for the predominant abundance in space: 1. Chemical inertness 2. Photostability Considering the fact that the abundance of atomic carbon is about 100 times higher than the abundance of any hydrocarbon molecule, the inertness towards the reaction with carbon atoms seems to be particularly important.

37 Pick up of atomic carbon by He droplets Our source Thermal evaporation Appl. Phys. Lett. 105, (2014).

38 C 6 D C, background R. I. Kaiser, I. Hahndorf, L. C. L. Huang, Y. T. Lee, H. F. Bettinger, P. V. Schleyer, H. F. Schaefer, and P. R. Schreiner, J. Chem. Phys. 110, 6091 (1999).

39 Mass spectrometry and calorimetry study of the reaction C 6 D C

40 Calorimetry study of the reaction C 6 D C E therm. = kj/mol E react. >> 270 kj/mol

41 C 6 D C, background R. I. Kaiser, I. Hahndorf, L. C. L. Huang, Y. T. Lee, H. F. Bettinger, P. V. Schleyer, H. F. Schaefer, and P. R. Schreiner, J. Chem. Phys. 110, 6091 (1999).

42 Products of C 10 H 8 + C reaction b3lyp/6-311+g(d,p), reaction energies are given in kj/mol

43 Reaction pathway for C 10 H 8 + C, singlet channel

44 Reaction pathway for C 10 H 8 + C, triplet channel

45 Mass spectrometry study of the reaction C 10 D C

46 Reaction pathway for C 10 H 8 + C, triplet channel + 92 kj/mol 231 kj/mol 79 kj/mol 402 kj/mol

47 Reactions of C atoms with anthracene 50 0 Ion signal change (khz) kj/mol Mass (amu)

48 Reactions of C atoms with coronene 2 13 CC 24 H CC 24 H C 2 C 23 H 12 Ion signal change (khz) CC 23 H 12 C 24 H Mass (amu)

49 Products of the reactions of C atoms with coronene

50 Interstellar dust and diamonds? W. C. Saslaw and J. E. Gaustad, Nature 221, 160 (1969)