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Jordy BouwmanSackler 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)
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?
Other options?
• PAHs are known to be strong UV/VIS absorbers
• Common interstellar ice constituents are transparent for > 240 nm
Near UV/VIS spectroscopy!
Sensitive Solid-State Spectrometer
J. Bouwman, D.M. Paardekooper, H.M. Cuppen, H. Linnartz, L.J. Allamandola, ApJ, in press (2009)
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
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
Reaction rates
Py = Pyrene
Py.+ = Pyrene cation
PyH. = unknownPi = Product ikjj = reaction rate jj
Reaction scheme:
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
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)
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
Trapping of cations• Irradiate to obtain maximum cation signal
J. Bouwman et al., Astronomy and Astrophysics, in prep.
T=25 K