Electronic spectroscopy of neutral and ionized PAHs in inert gas m - - PowerPoint PPT Presentation

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Electronic spectroscopy of neutral and ionized PAHs in inert gas m - - PowerPoint PPT Presentation

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International Conference on Interstellar Dust, Molecules, and Chemistry Pune, India, 22 25 November 2011 Electronic spectroscopy of neutral and ionized PAHs in inert gas m atrices Mathias Steglich Laboratory Astrophysics and Cluster

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  • M. Steglich (FSU Jena)

International Conference on Interstellar Dust, Molecules, and Chemistry Pune, India, 22 – 25 November 2011

Electronic spectroscopy of neutral and ionized PAHs in inert gas m atrices

Mathias Steglich Laboratory Astrophysics and Cluster Physics Group Institute of Solid State Physics Friedrich Schiller University Jena

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  • M. Steglich (FSU Jena)

Outline Introduction: Astrophysical background and experimental techniques

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Absorption spectra of PAH mixtures

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Absorption spectra of ionized PAHs

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  • M. Steglich (FSU Jena)

Outline Introduction: Astrophysical background and experimental techniques

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Absorption spectra of PAH mixtures

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Absorption spectra of ionized PAHs

3 Introduction

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  • M. Steglich (FSU Jena)

I nterstellar extinction curve: DI Bs & UV bum p

Introduction

4 / 18 Xiang et al., ApJ 733 (2011) 91 → no correlation bet- w een nine strong DI Bs ( 5 7 0 - 6 3 8 nm ) and the UV bum p ( 2 1 7 .5 nm ) Gredel et al., A&A 530 (2011) A26; Salama et al., ApJ 728 (2011) 154 → for λ < 4 0 0 nm , no narrow DI B-like ab- sorption bands that could be caused by polyatom ic ( N> 3 ) m olecules

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  • M. Steglich (FSU Jena)

Arom atic I R em ission bands

Introduction [ Tielens, 2008]

~ 1 nm ; ca. 2 0 hexagons;

  • ca. 5 0 C and 2 0 H atom s

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  • M. Steglich (FSU Jena)

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Absorption spectra via m atrix isolation spectroscopy

Introduction

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  • M. Steglich (FSU Jena)

PAH synthesis via laser pyrolysis

Introduction

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  • M. Steglich (FSU Jena)

Outline Introduction: Astrophysical background and experimental techniques

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Absorption spectra of PAH mixtures

2

Absorption spectra of ionized PAHs

3 PAH mixtures

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  • M. Steglich (FSU Jena)

HPLC analysis of soluble condensate

PAH mixtures

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  • M. Steglich (FSU Jena)

MALDI -TOF m easurem ents of laser pyrolysis condensate

PAH mixtures

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  • M. Steglich (FSU Jena)

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Absorption spectra of different PAH m ixtures in Ne @ 6 K

PAH mixtures

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  • M. Steglich (FSU Jena)

Absorption spectra of PAH m ixtures as thin solid film

PAH mixtures

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  • M. Steglich (FSU Jena)

Sem i-em pirically calculated absorption spectra of PAH m ixtures

PAH mixtures

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  • M. Steglich (FSU Jena)

Outline Introduction: Astrophysical background and experimental techniques

1

Absorption spectra of PAH mixtures

2

Absorption spectra of ionized PAHs

3 Ionized PAHs

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  • M. Steglich (FSU Jena)

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Com parison of specific PAHs in neutral and ionized form

Ionized PAHs

wavelength [nm] wavenumber [μm-1] absorbance ionized DBR in Ne (7 K) neutral DBR in Ne (7 K) wavelength [nm] wavenumber [μm-1] ionized HBC in Ne (7 K) neutral HBC in Ne (7 K)

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  • M. Steglich (FSU Jena)

I onized HBC ( C4 2H 1 8) and the DI Bs

Ionized PAHs

16 / 18 “all-benzenoid” PAH HBC → high stability ( higher abundance than other sim ilarly-sized PAHs?)

[ T. P. Troy & T. W. Schmidt, MNRAS 371 (2006) L41]

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  • M. Steglich (FSU Jena)

Sum m ary

17 / 18 The interstellar UV bum p can arise from π-π* resonances of sm all arom atic islands ( ~ 5 0 C atom s) as they are present, e.g., in the PAHs that are responsible for the arom atic I R em ission bands. No absorption band specific for a certain PAH ( m easured so far) has been detected in the I SM. “Norm al“ PAHs are probably not responsible for the DI Bs.

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  • M. Steglich (FSU Jena)

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  • M. Steglich, C. Jäger, G. Rouillé, F. Huisken, H. Mutschke, Th. Henning, ApJ 7 1 2 (2010) L16

“Electronic spectroscopy of medium-sized polycyclic aromatic hydrocarbons: Implications for the carriers of the 2175 Å UV bump“ (arXiv: 1002.3529)

  • M. Steglich, J. Bouwman, F. Huisken, Th. Henning, ApJ 7 4 2 (2011) 2

“Can neutral and ionized polycyclic aromatic hydrocarbons be carriers of the ultraviolet extinction bump and the diffuse interstellar bands?“ (arXiv: 1108.2972)

  • M. Steglich, Y. Carpentier, C. Jäger, F. Huisken, Th. Henning, in preparation for A&A

“On the smoothness of the interstellar extinction curve in the UV: Comparison with recent labora- tory measurements of PAH mixtures“

  • R. Gredel, Y. Carpentier, G. Rouillé, M. Steglich, F. Huisken, Th. Henning, A&A 5 3 0 (2011) A26

“Abundances of PAHs in the ISM: Confronting observations with experimental results“ (arXiv: 1102.3775) Papers related to this talk Acknow ledgem ents

Laboratory Astrophysics Group, FSU Jena: F. Huisken, G. Rouillé, C. Jäger, Y. Carpentier Astrophysical Institute, FSU Jena: H. Mutschke, G. Born MPI for Astronomy, Heidelberg: Th. Henning, R. Gredel Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden: H. Linnartz, J. Bouw m an TU Dresden: H.-J. Knölker; MPI for Polymer Research, Mainz: K. Müllen Financial support: DFG, MPI for Astronomy