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 Title: Electronic spectroscopy of trapped pah photofragments Author(s): Joblin, Christine Contributor(s): Bonnamy, Anthony Subject(s): Spectroscopy in Traps Abstract: The PIRENEA set-up combines an ion cyclotron resonance cell mass spectrometer with cryogenic cooling in order to study the physical and chemical properties of polycyclic aromatic hydrocarbons (PAHs) of astrophysical interest. In space, PAHs are submitted to UV photons that lead to their dissociation. It is therefore of interest to study fragmentation pathways and search for species that might be good interstellar candidates because of their stability\footnote{J.~Montillaud, C.~Joblin, D.~Toublanc, \textit{Astron. \& Astrophys.} \underline{\textbf{552}} (2013), id.A15}. Electronic spectroscopy can bring major insights into the structure of species formed by photofragmentation. This is also a way to identify new species in space as recently illustrated in the case of C$_{60}^+$\footnote{E.K.~Campbell, M.~Holz, D.~Gerlich, and J.P.~Maier, \textit{Nature} \underline{\textbf{523}} (2015), 322-323}. In PIRENEA, the trapped ions are not cold enough, and thus we cannot use complexation with rare gas in order to record spectroscopy, as was nicely performed in the work by Campbell et al. on C$_{60}^+$. We are therefore using the dissociation of the trapped ions themselves instead, which requires in general a multiple photon scheme\footnote{F.~Useli-Bacchitta, A.~Bonnamy, G.~Malloci, et al., \textit{Chem.~Phys.} \underline{\textbf{371}} (2010), 16-23J.~Zhen, A. ~Bonnamy, G.~Mulas, C.~Joblin, \textit{Mol. Astrophys.} \underline{\textbf{2}} (2015), 12-17}. This leads to non-linear effects that affect the measured spectrum. We are working on improving this scheme in the specific case of the photofragment obtained by H-loss from 1-methylpyrene cation (CH$_3$-C$_{16}$H$_{9}^+$). A recent theoretical study has shown that a rearrangement can occur from 1-pyrenemethylium cation (CH$_2$-C$_{16}$H$_{9}^+$) to a system containing a seven membered ring (tropylium like pyrene system)\footnote{M.~Rapacioli, A.~Simon, C.C.M.~Marshall, et al., \textit{J. Phys. Chem. A} \underline{\textbf{119}} (2015), 12845-12854}. This study also reports the calculated electronic spectra of both isomers, which are specific enough to distinguish them, and as a function of temperature. We will present experiments that have been performed to study the photophysics of these ions using the PIRENEA set-up and a two-laser scheme for the action spectroscopy. Acknowledgments\footnote{European Research Council grant ERC-2013-SyG, Grant Agreement n.~610256 NANOCOSMOS.} Issue Date: 2016-06-21 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper/Presentation Type: Text Language: En URI: http://hdl.handle.net/2142/91456 Rights Information: Copyright 2016 by the authors Date Available in IDEALS: 2017-01-26
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