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

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 M. Steglich (FSU Jena) 1 / 18

Outline Introduction: Astrophysical background and 1 experimental techniques Absorption spectra of PAH mixtures 2 Absorption spectra of ionized PAHs 3 M. Steglich (FSU Jena) 2 / 18

Introduction Outline Introduction: Astrophysical background and 1 experimental techniques Absorption spectra of PAH mixtures 2 Absorption spectra of ionized PAHs 3 M. Steglich (FSU Jena) 3 / 18

Introduction I nterstellar extinction curve: DI Bs & UV bum p 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 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 ) M. Steglich (FSU Jena) 4 / 18

Introduction Arom atic I R em ission bands ~ 1 nm ; ca. 2 0 hexagons; ca. 5 0 C and 2 0 H atom s [ Tielens, 2008] M. Steglich (FSU Jena) 5 / 18

6 / 18 Absorption spectra via m atrix isolation spectroscopy M. Steglich (FSU Jena) Introduction

7 / 18 PAH synthesis via laser pyrolysis M. Steglich (FSU Jena) Introduction

PAH mixtures Outline Introduction: Astrophysical background and 1 experimental techniques Absorption spectra of PAH mixtures 2 Absorption spectra of ionized PAHs 3 M. Steglich (FSU Jena) 8 / 18

9 / 18 HPLC analysis of soluble condensate M. Steglich (FSU Jena) PAH mixtures

PAH mixtures MALDI -TOF m easurem ents of laser pyrolysis condensate M. Steglich (FSU Jena) 10 / 18

PAH mixtures Absorption spectra of different PAH m ixtures in Ne @ 6 K M. Steglich (FSU Jena) 11 / 18

PAH mixtures Absorption spectra of PAH m ixtures as thin solid film M. Steglich (FSU Jena) 12 / 18

PAH mixtures Sem i-em pirically calculated absorption spectra of PAH m ixtures M. Steglich (FSU Jena) 13 / 18

Ionized PAHs Outline Introduction: Astrophysical background and 1 experimental techniques Absorption spectra of PAH mixtures 2 Absorption spectra of ionized PAHs 3 M. Steglich (FSU Jena) 14 / 18

Ionized PAHs Com parison of specific PAHs in neutral and ionized form wavenumber [ μ m -1 ] absorbance ionized DBR in Ne (7 K) wavenumber [ μ m -1 ] neutral DBR in Ne (7 K) ionized HBC in Ne (7 K) wavelength [nm] neutral HBC in Ne (7 K) wavelength [nm] M. Steglich (FSU Jena) 15 / 18

Ionized PAHs I onized HBC ( C 4 2 H 1 8 ) and the DI Bs “all-benzenoid” PAH HBC → high stability ( higher abundance than other sim ilarly-sized PAHs?) [ T. P. Troy & T. W. Schmidt, MNRAS 371 (2006) L41] M. Steglich (FSU Jena) 16 / 18

Sum m ary 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. M. Steglich (FSU Jena) 17 / 18

Papers related to this talk 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) 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) 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“ 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 M. Steglich (FSU Jena) 18 / 18