Spectroscopy of large PAHs

Laboratory studies and comparison to the Diffuse Interstellar Bands

¹ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
² Space Science Division, NASA-Ames Research Center, Moffett Field CA 94035, USA
³ ESA Research Support Division, ESTEC/SCI-SR, PO Box 229, 2200 AG, Noordwijk, The Netherlands
⁴ PAH Forschungs Institut, Flurstrasse 17, 86926 Greifenberg/Ammersee, Germany

Corresponding author: R. Ruiterkamp, ruiterka@strw.leidenuniv.nl

Received: 16 January 2002
Accepted: 27 March 2002

Abstract

Polycyclic Aromatic Hydrocarbons (PAHs) are thought to be the carriers of the ubiquitous infrared emission bands (UIBs). Data from the Infrared Space Observatory (ISO) have provided new insights into the size distribution and the structure of interstellar PAH molecules pointing to a trend towards larger-size PAHs. The mid-infrared spectra of galactic and extragalactic sources have also indicated the presence of 5-ring structures and PAH structures with attached side groups. This paper reports for the first time the laboratory measurement of the UV–Vis–NIR absorption spectra of a representative set of large PAHs that have also been selected for a long duration exposure experiment on the International Space Station ISS. PAHs with sizes up to 600 amu, including 5-ring species and PAHs containing heteroatoms, have been synthesized and their spectra measured using matrix isolation spectroscopy. The spectra of the neutral species and the associated cations and anions measured in this work are also compared to astronomical spectra of Diffuse Interstellar Bands (DIBs).