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 Title: Optical Spectrum Of The Adamantane Radical Cation Author(s): Crandall, Parker B. Contributor(s): Dopfer, Otto; Förstel, Marko; Müller, David Subject(s): Action spectroscopy (incl. PE, PD, PI, LIR) Abstract: Known for their stable structural and thermal properties, diamondoids and their radical cations are viable candidates as carriers for diffuse interstellar bands.$^{1}$ While previous diamondoid research has mainly focused on neutral molecules and their derivatives, little is known about their radical cations, which may form in interstellar environments by ionizing radiation.$^{2}$ We report the first experimental optical spectrum of the simplest diamondoid cation, the adamantane radical cation (\chem{C_{10}H_{16}}$^{+}$), obtained via electronic photodissociation spectroscopy at 5 K between 310–1000 nm. The optical spectrum reveals a broad peak between 420–850 nm, assigned to the D$_{2}$($^{2}$E) $\gets$ D$_{0}$($^{2}$A$_{1}$) transition. This feature exhibits no vibrational structure, despite an experimental temperature below 20 K, due to lifetime broadening and/or Franck-Condon congestion. A second band system originating at 345 nm does reveal a vibrational progression and is attributed to the overlapping D$_{5}$($^{2}$A$_{1}$)/D$_{6}$($^{2}$E) $\gets$ D$_{0}$($^{2}$A$_{1}$) transitions split by the Jahn-Teller effect. Comparison of the spectrum with known diffuse interstellar bands suggests that \chem{C_{10}H_{16}}$^{+}$ is not likely to be a carrier. However, the strong absorption features in the UV to near IR show promise in the investigation of higher order diamondoid cations as potential candidates.$^{3}$ $\bigskip$ \noindent [1] T. Henning and F. Salama 1998, Science, 282, 2204. [2] C. W. Bauschlicher Jr., Y. Liu, A. Ricca, A. L. Mattioda, L. J. Allamandola, 2007, ApJ, 671, 458. [3] P. B. Crandall, D. M\"{u}ller, M. F\"{o}rstel, J. Leroux, O. Dopfer, 2020, ApJL, 900, L20. Issue Date: 2021-06-24 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/111313 Date Available in IDEALS: 2021-09-24
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