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Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices
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Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Dec 13, 2015

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Page 1: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Jordy BouwmanSackler Laboratory for Astrophysics, Leiden Observatory

Shining light on PAHs in interstellar ices

Page 2: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

IR absorption

PDR

Bauschlicher et al., ApJ 697, 311, 2009

Page 3: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Wealth of frozen species

E.L. Gibb et al., ApJ 536, 347 (2000)

IR spectrum towards a high mass protostar and laboratory spectrum

H2Ostretch

H2Obend

H2OLib.

CO

Bouwman et al., A&A, 476, 995 (2007)

Page 4: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

IR Emission bands

PDR

3.3, 6.2, 7.7, 8.6, and 11.3 m

Page 5: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

PAHs in ices

• PAHs are likely to freeze out on cold grains and are incorporated in ices…

1.How can we study these mixtures spectroscopically?

2.How do PAHs trapped in ices behaveupon VUV irradiation?

Page 6: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

IR spectroscopy

• Anthracene:H2O ice 1:70 mixture

Bernstein et al., ApJ, 664, 1264 (2007)

Page 7: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

PAHs in ices

E.L. Gibb et al., ApJ 536, 347 (2000)

Bernstein et al., ApJ, 664, 1264 (2007)

Page 8: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Other options?

• PAHs are known to be strong UV/VIS absorbers

• Common interstellar ice constituents are transparent for > 240 nm

Near UV/VIS spectroscopy!

Page 9: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Sensitive Solid-State Spectrometer

J. Bouwman, D.M. Paardekooper, H.M. Cuppen, H. Linnartz, L.J. Allamandola, ApJ, in press (2009)

Page 10: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Pyrene:H2O ice spectrum

J. Bouwman et al., Astronomy and Astrophysics, in prep.

Page 11: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Assignment 400 nm band

• Not a direct photon product!

• Evidence for HCO. radicals

Page 12: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Time and temperature evolution

Ionization is most efficient at low temperatures

Photoproduct band growth faster at high temperatures

PyH. nm band more prominent at high temperaturesJ. Bouwman et al., Astronomy and Astrophysics, in prep.

T=11 K T=100 K

Page 13: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Chemical evolution• VUV irradiation while measuring spectra

every 10 s permits real time tracking

J. Bouwman et al., Astronomy and Astrophysics, in prep.

T=25 K

Page 14: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Reaction rates

Py = Pyrene

Py.+ = Pyrene cation

PyH. = unknownPi = Product ikjj = reaction rate jj

Reaction scheme:

Page 15: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Pyrene H2O ice photochemistry

• Evidence for PAH-ion mediated (photo-) chemistry

• Two different temperature regimesReaction scheme:

low T regimeHigh T regime

Py = PyrenePy+ = Pyrene cation

PyH. = unknownPi = Product iKjj = reaction rate jj

Page 16: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Astrochemical picture

Bernstein, Sandford, Allamandola , Sci. Am. 7, p26 (1999)

Page 17: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Conclusions

• The setup shows great potential for both spectroscopy and kinetics

• PAH reaction paths are temperature dependent

• PAHs in H2O ice are readily ionized• Ions are stabilized in water ice and play a

previously neglected role in ice chemistry• VLT UV/VIS observations of embedded

objects are awaiting data reduction (help)

Page 18: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

AcknowledgementsThanks to the Sackler laboratory group:

€€€

• Harold Linnartz• Herma Cuppen• Lou Allamandola• Claire Romanzin• Arthur Bakker• Daniël Paardekooper

• Nadine Wehres• Sergio Ioppolo• Karoliina Isokoski• Karin Öberg• Edith Fayolle• Ankan Das

Page 19: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Trapping of cations• Irradiate to obtain maximum cation signal

J. Bouwman et al., Astronomy and Astrophysics, in prep.

T=25 K

Page 20: Jordy Bouwman Sackler Laboratory for Astrophysics, Leiden Observatory Shining light on PAHs in interstellar ices.

Normalized pyrene cation decay

• Double exponential decay at 10 K

1 = 2 hrs

2 = 351 hrs

J. Bouwman et al., Astrophysical Journal, in press (2009)