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 Title: The Electric Quadrupole Spectra Of Diatomic Molecules Author(s): Somogyi, Wilfrid Contributor(s): Yurchenko, Sergei N. Subject(s): Linelists Abstract: Owing to their molecular symmetry, many transitions of homonuclear diatomic molecules are forbidden in the electric dipole approximation. Instead their spectra are dominated by higher order transition moments, including the magnetic dipole moment and electric quadrupole moment. \begin{wrapfigure}{r}{0pt} \includegraphics[width=.4\linewidth]{H2XQMhitran.eps} \end{wrapfigure} Here we present a new implementation of electric quadrupole transition moments in \textsc{Duo}\footnote{S.~N. Yurchenko, L.~Lodi, J.~Tennyson, A.~V. Stolyarov, \emph{Comput. Phys. Commun.}, 2016, \textbf{202}, 262 -- 275; publicly available at \textit{https://github.com/Trovemaster/Duo}.}. The implementation is validated against the highly accurate linelist of Roueff et al. \footnote{The full infrared spectrum of molecular hydrogen, Astron. Astrophys, 630 (2019)} for rovibrational transitions of the hydrogen molecule. We also perform ab initio calculations for potential energy curves (PECs), electric quadrupole moment curves (EQCs), and spin-orbit coupling curves (SOCs) and demonstrate rovibronic linestrength calculations for the three lowest lying states ($X^3\Sigma_g^-$, $a^1\Delta_g$ and $b^2\Sigma_g^+$) of molecular oxygen. Further demonstrations are provided for various other molecules of interest, including CO and HF as part of the ExoMol project \footnote{J.~Tennyson et al. \emph{J. Quant. Spectrosc. Radiat. Transf.}, 2020, \textbf{255}, 107228; \textit{www.exomol.com}.}. Absorption cross-sections are calculated using the \textsc{ExoCross} program\footnote{S.~N. {Yurchenko}, A.~F. {Al-Refaie}, J.~{Tennyson}, \emph{Astron. Astrophys};, 2018, \textbf{614}, A131; publicly available at \textit{https://github.com/Trovemaster/ExoCross}.}. Issue Date: 2021-06-22 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/111446 Date Available in IDEALS: 2021-09-24
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