Isomerization of phenanthrene dication studied by tagging photodissociation ion spectroscopy and DFT calculations

30 January 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

The search for the chemical structures that account for diffuse interstellar bands remains the main challenge in astrochemistry. It relies on experimental verification of structures obtained from stable isomers in laboratory conditions. The actual interstellar medium, however, is exposed to much harsher conditions. Herein we demonstrate the isomerization of small, doubly charged polyaromatic hydrocarbon phenanthrene obtained by electron ionization at relatively high electron energies. We performed electronic and vibrational tagging photodissociation spectroscopy measurements. Our results show that phenanthrene dication has a broad visible spectrum, making it unsuitable for DIB search. We also detected another C14H102+ isomer, originating from the isomerization of phenanthrene dication during the ionization process. Hole-burning spectroscopy experiments provided the IR spectrum of an isomer which could be assigned based on DFT calculations as a fully conjugated system representing the global minimum on the C14H102+ potential energy surface.

Keywords

DIB
ISM
PAH
phenanthrene
isomerization
tagging
photodissociation
spectroscopy

Supplementary materials

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Description
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Supporting information
Description
Results of DFT calculations
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