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 Title: Ab Initio Study Of The Highly Excited Electronic States Of C2 And Its Photodissociation Author(s): Xu, Zhongxing Contributor(s): Crabtree, Kyle N.; Ng, Cheuk-Yiu; Jackson, William M.; Federman, Steven; Wang, Lee-Ping Subject(s): Photodissociation and photochemistry Abstract: Dicarbon (\ce{C2}) is one of the most abundant molecules in space and has been detected in different astronomical environments, including the interstellar medium, comets, and stars. In diffuse clouds, the dominant destruction pathway for \ce{C2} is photodissociation by UV photons through the $F\,^1\Pi_u$ state and other higher $^1\Pi_u$ and $^1\Sigma_u^+$ states excited from the ground $X\,^1\Sigma_g^+$ state. However, the only laboratory study of the $F\,^1\Pi_u$ state was more than half a century ago and did not provide detailed information about its photodissociation, while no MRCI+Q level calculation has been done on the $F$ state to date. Thus, considerable uncertainty exists about the photodissociation rate of \ce{C2} in space and its atomic branching ratios, limiting the accuracy of simulations given by astrochemical models. Here we present a high-level \textit{ab initio} study of \ce{C2} photodissociation, focusing on the $F\,^1\Pi_u - X\,^1\Sigma_g^+$ transition. Potential energy curves of \ce{C2} electronic states were calculated at the SA-CASSCF/MRCI+Q level using the aug-cc-pV5Z basis set with additional diffuse functions. To represent the Rydberg state nature of $F$ state, the active space consisted of the valence orbitals and several additional $\sigma_g$ orbitals. A total of 57 potential energy curves for singlet, triplet and quintet states were calculated, as well as transition dipole moments, nonadiabatic coupling matrix elements, and spin-orbit couplings. The $F$ state lies near three $^3\Pi_u$ states that are likely responsible for its predissociation via spin-orbit coupling. Issue Date: 2021-06-25 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/111414 Date Available in IDEALS: 2021-09-24
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