Boschman, Leon
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Publication date: 2017
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Boschman, L. (2017). Chemistry and photophysics of polycyclic aromatic hydrocarbons in the interstellar medium. Rijksuniversiteit Groningen.
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Chemistry and Photophysics of
Polycyclic Aromatic Hydrocarbons
in the Interstellar Medium
The experimental research presented in this PhD thesis was performed in the research group Quantum Interactions and Structural Dynamics (QISD). Up to 31-12-2013 this group was embedded in the Kernfysisch Versneller Instituut (KVI) under the name Atomic and Molecular Physics (AMP). From 01-01-2014 the group is part of the Zernike Institute of Advanced Materials at the University of Groningen, The Netherlands.
The numerical and astronomical work presented in this PhD thesis was performed at the Kapteyn Astronomical Institute at the University of Groningen, The Netherlands.
The work was funded by the Netherlands Organization for Scientific Research (NWO; VIDI project 639.042.017). The beamtimes were allocated by the Helmholtz Zentrum Berlin and financially supported by the European Commu-nity’s Seventh Framework Programme.
Cover design: Borris Boschman
Chemistry and Photophysics of
Polycyclic Aromatic Hydrocarbons
in the Interstellar Medium
Proefschrift
ter verkrijging van de graad van doctor aan de Rijksuniversiteit Groningen
op gezag van de
rector magnificus prof. dr. E. Sterken en volgens besluit van het College voor Promoties.
De openbare verdediging zal plaatsvinden op vrijdag 6 januari 2017 om 16.15 uur
door
Leon Micha¨el Primius Valentijn Boschman geboren op 30 september 1988
Beoordelingscommissie Prof. dr. I.E.E. Kamp Prof. dr. F. Dulieu
Prof. dr. W.M.G. Ubachs
ISBN 978-90-367-9436-7 (printed version) ISBN 978-90-367-9435-0 (electronic version)
Contents
1 Introduction 1
1.1 The Formation of H2 in Space . . . 2
1.2 PAHs in the ISM . . . 7
1.2.1 Molecular structure of PAHs . . . 8
1.2.2 Observational Evidence . . . 11
1.2.3 Observations . . . 13
1.3 Atomic, Molecular, and Photonic Interactions on PAHs . . 16
1.3.1 PAH Chemistry . . . 17
1.3.2 Photoprocessing of PAHs . . . 18
1.4 Modeling of PAHs in the ISM . . . 20
1.5 Contents of this Thesis . . . 21
2 The Experimental Setup 23 2.1 Electrospray Ionization . . . 24
2.2 Ion Funnel . . . 26
2.3 Ion Guide . . . 27
2.4 Mass Filter . . . 28
2.5 Paul Ion Trap . . . 29
2.6 Mass Spectrometer . . . 29
2.7 Hydrogen Source . . . 30
2.7.1 Placement of the Hydrogen Source . . . 32
3 Hydrogenation of PAH Cations 35 3.1 Introduction . . . 36
4.1 Introduction . . . 48 4.2 Results . . . 49 4.2.1 Experimental results . . . 49 4.2.2 Theoretical results . . . 51 4.3 Discussion . . . 56 4.4 Methods . . . 58 4.4.1 Experiments . . . 58 4.4.2 DFT calculations . . . 59 5 VUV photoabsorption 63 5.1 Introduction . . . 64 5.2 Experiment . . . 66
5.3 Data analysis, Results, and Discussion . . . 70
5.3.1 Coronene . . . 71
5.3.2 Superhydrogenated coronene . . . 74
5.4 Astrophysical Application . . . 76
5.4.1 Modeling of the experimental results . . . 77
5.4.2 The Photodissociation of PAHs . . . 80
5.5 Conclusion . . . 83
6 H2 formation on PAHs in photodissociation regions 87 6.1 Introduction . . . 88
6.2 Model . . . 91
6.2.1 PAHs . . . 93
6.2.2 H2 formation on dust grains . . . 97
6.2.3 H2 photodissociation . . . 98
6.2.4 Computations . . . 99
6.3 Results . . . 100
6.3.1 Spatial distribution of coronene . . . 101
6.3.2 H2 formation rates . . . 103
6.3.3 Impact of H2 formation . . . 105
Contents vii 6.4.1 Impact of uncertainties . . . 108 6.4.2 Expectations for a population of large PAHs . . . . 110 6.5 Conclusions . . . 112
7 Summary 117
7.1 Outlook & Future Experiments . . . 120
Samenvatting 125
Dankwoord 133
Bibliography 137
