Cryochemistry in the Inert and Interstellar Media

Cryochemistry in the inert and interstellar media

Serge A. Krasnokutski

Friedrich Schiller MPI for Astronomy, University of Jena, Königstuhl 17,69117 07740 Jena, Germany Heidelberg, Germany Holes in heaven Herschel, W., Phil. Trans. 75, 213 (1785)

T = 10 - 50 K The Boomerang Nebula T = 1 K Motivation

k = A e-Ea / RT T = 0.37 K

T = 10 - 50 K Reaction of Al atoms with oxygen molecules

Al + O2 →AlO + O

J. Phys. Chem. A 101, 9988 (1997) Reaction of Si atoms with oxygen molecules

T = 0.37 K k > 5 × 10-14 cm3 mol-1 s-1

6.7 × 10-29

0.1 0.37 1

1.77 × 10-82 1.46 × 10-16 Astron. Astrophys. 372, 1064 (2001) J. Phys. Chem. A 114, 13045 (2010) Chemical models of reactions in the ISM

Gas-phase or grain-surface reactions?

Grain-surface reactions A + B → AB Gas-phase reactions A + B → C + D

desorption accretion

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. The matrix isolation scheme The matrix isolation experimental setup Formation of (SiO)n clusters in Ne matrix

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

Astrophys. J. 782, 10pp (2014) The He droplet experimental setup 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. The properties of helium nanodroplets

(푧)푘 푃 푧 = exp⁡(−푧) 푘 푘!

Angew. Chem. 43, 2622 (2004). Monitoring chemical reactions in He droplets

1. Calorimetry measurements n > 1000 2. Observation of chemiluminescence 3. Mass spectrometric detection 4. Laser spectroscopic detection 10000 < n < 50000

Reactions inside helium droplets

-1 1) Large droplets n1 > 20000 Er = (n1 – n2) × 5 cm

2) Small droplets n1 < 10000 d = 4.44 n1/3 Å Product ejection The determination of the mean sizes of He droplets

To measure the average 1.1 number of He atoms inside 1.0 a He droplet

0.9 79 Å

0.8 91 Å

mass (arb. units) 100 Å

2 10

0.7 112 Å mbar) -9 0.6 8 0.5 130 Å

Ion signal at He 0.4 6 0 50 100 150 200 250 300 Time (s) 4

To measure the average He droplet diameter 2

Pressure in the detector chamber (10 0 5 10 15 20 Thousand He atoms per droplet Calorimetry study of Al + O2 reaction

J. Phys. Chem. A, 115, 7120 (2011) Calorimetry study of (SiO)n cluster formation

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

Astrophys. J. 782, 10pp (2014) Detection of chemical reactions

1. Calorimetry measurements n > 1000 2. Observation of chemiluminescence 3. Mass spectrometric detection 4. Laser spectroscopic detection 10000 < n < 50000

Chemiluminescence study of Mg + O2 reaction

1.0 9 8 0.8 y = 0 mm 7 y = 1 mm 0.6 y = 2 mm 6 y = 3 mm 0.4 5 y = 4 mm y = 5 mm 0.2 4 3 CL intensity (arb. units) 0.0 40 2 n = 1

Light intensity (arb. unit) 1 30 n = 2 0 n = 3 0 10 20 30 40 50 60 70 80 90 n = 4 20 n = 5 Distance x (mm)

Probability (%) n = 6 0 0 2 4 6 8 10 12 14 16 -5 pMg (10 mbar)

1. CL results from electronically and vibrationally excited reaction products

(MgnO2, 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 5  104 s-1.

J. Phys. Chem. A 114, 7292 (2010) Detection of chemical reactions

1. Calorimetry measurements n > 1000 2. Observation of chemiluminescence 3. Mass spectrometric detection 4. Laser spectroscopic detection 10000 < n < 50000

Mass spectrometry study of Si + O reaction 2

Si only

Si + O2

SiO SiO2

ion signal Si2O Si2O2 Si2O3

20 40 60 80 100 120 mass (amu)

J. Phys. Chem. A, 114, 13045 (2010) Mass spectrometry study of Si + O2 reaction

O2 O4 O5

)

t i SiO SiO2 SiO3

T = 10 K

b (d = 13 nm) r He

(

OH2 OHO22 SiOH2 O SiO22 H O

n Si2 O Si22 O Si23 O

h Hen

Si SiOH Si2 Si3 Si4 20 40 60 80 100 120 Mass (amu)

J. Phys. Chem. A, 114, 13045 (2010) Detection of chemical reactions

• 1. Calorimetry measurements n > 1000 • 2. Observation of chemiluminescence • 3. Mass spectrometric detection • 4. Laser spectroscopic detection n < 30000

Laser spectroscopic detection

Laser induce fluorescence Resonance two photons (LIF) ionization (R2PI)

• No mass selectivity • Mass selectivity • Average sensitivity • High sensitivity • Works only for luminescent • Works for most of the molecules molecules

R2PI spectra of Fe atoms in the gas phase and solvated in helium droplets

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

J. Phys. Chem. A 118, 2612 (2014) Formation of large clusters inside He droplets

(SiO) n

Si + H2O

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

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

Astrophys. J. 782, 10pp (2014) 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 217.5 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 (C6H6) 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). 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. Pick–up of atomic carbon by He droplets

Our source

Thermal evaporation

Appl. Phys. Lett. 105, 113506 (2014). 13 C6D6 + 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). Mass spectrometry and calorimetry study of the reaction 13 C6D6 + C 13 Calorimetry study of the reaction C6D6 + C

Etherm. = 274.6 kJ/mol

Ereact. >> 270 kJ/mol 13 C6D6 + 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). Products of C10H8 + C reaction

339.7 402.0 116.9 222.6

336.1

321.1 324.0

363.3 b3lyp/6-311+g(d,p), reaction energies are given in kJ/mol

Reaction pathway for C10H8 + C, singlet channel

0 + -110.3 -172.3

-181.3 -222.6

-324.0

-363.3

-402.0 Reaction pathway for C10H8 + C, triplet channel

0 + 25.1

-60.3

-90

-92 -193.1

-322.6

-349.7 13 Mass spectrometry study of the reaction C10D8 + C Reaction pathway for C10H8 + C, triplet channel

92 kJ/mol 231 kJ/mol 79 kJ/mol

402 kJ/mol Reactions of C atoms with anthracene

-50

-100

-150 Ion signalIon change (kHz) 372.1 kJ/mol

-200

150 160 170 180 190 200 210 Mass (amu) Reactions of C atoms with coronene

2 13CC H 24 11 13CC H 24 12 1 13C C H 2 23 12

-1 13CC H 23 12

-2

Ion signal change (kHz) C H 24 12 -3

270 280 290 300 310 320 Mass (amu) Products of the reactions of C atoms with coronene

71.8 23.9 134.5

322.4 Interstellar dust and diamonds?

W. C. Saslaw and J. E. Gaustad, Nature 221, 160 (1969)