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Laboratory spectroscopy and astronomical significance of the fully-benzenoid PAH triphenylene and its cation

Kofman, V.; Sarre, Peter; Hibbins, R.E.; ten Kate, I.L.; Linnartz, H.

Authors

V. Kofman

Peter Sarre

R.E. Hibbins

I.L. ten Kate

H. Linnartz



Abstract

Triphenylene (C18H12) is a highly symmetric polycyclic aromatic hydrocarbon (PAH) molecule with a ‘fully-benzenoid’ electronic structure. This confers a high chemical stability compared with PAHs of similar size. Although numerous infrared and UV-visible experimental spectroscopic and theoretical studies of a wide range PAHs in an astrophysical context have been conducted, triphenylene and its radical cation have received almost no attention. There exists a huge body of spectroscopic evidence for neutral and ionised PAHs in astrophysical sources, obtained principally through detection of infrared emission features that are characteristic of PAHs as a chemical class. However, it has so far not proved possible to identify spectroscopically a single isolated PAH in space, although PAHs including triphenylene have been detected mass spectrometrically in meteorites. In this work we focus on recording laboratory electronic spectra of neutral and ionised triphenylene between 220 and 780 nm, trapped in H2O ice and solid argon at 12 K. The studies are motivated by the potential for spectroscopic astronomical detection of electronic absorption spectra of PAHs in ice mantles on interstellar grains as discussed by Linnartz (2014), and were undertaken also in a cold Ar matrix to provide guidance as to whether triphenylene (particularly in its singly positively ionised form) could be a viable candidate for any of the unidentified diffuse interstellar absorption bands. Based on the argon-matrix experimental results, comparison is made with previously unpublished astronomical spectra near 400 nm which contain broad interstellar absorption features consistent with the predictions from the laboratory matrix spectra, thus providing motivation for the recording of gas-phase electronic spectra of the internally cold triphenylene cation.

Journal Article Type Article
Publication Date Jun 30, 2017
Journal Molecular Astrophysics
Electronic ISSN 2405-6758
Peer Reviewed Peer Reviewed
Volume 7
APA6 Citation Kofman, V., Sarre, P., Hibbins, R., ten Kate, I., & Linnartz, H. (2017). Laboratory spectroscopy and astronomical significance of the fully-benzenoid PAH triphenylene and its cation. Molecular astrophysics, 7, doi:10.1016/j.molap.2017.04.002
DOI https://doi.org/10.1016/j.molap.2017.04.002
Keywords Astrochemistry; Molecular processes; Methods: laboratory; techniques: spectroscopic; ISM: Molecules
Publisher URL http://www.sciencedirect.com/science/article/pii/S2405675817300039
Copyright Statement Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by-nc-nd/4.0

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Copyright Statement
Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by-nc-nd/4.0





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