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Author(s):Laws, Benjamin A.
Contributor(s):Gibson, Stephen T.
Subject(s):Small molecules
Abstract:\begin{wrapfigure} {r}{0pt} \includegraphics[scale=0.47]{C2VMI355nm.eps} \end{wrapfigure} At first glance dicarbon, C$_2$, would appear to be a very simple homonuclear diatomic molecule. However the bonding structure of C$_2$ has long been a topic of debate, with different qualitative theories predicting a C$-$C bond order of 2, 3, or even 4\footnote{R. M. Macrae, \emph{Sci. Prog.} {\bf99}, 1 (2016)}. Recent evidence for a quadruply bonded dicarbon has been provided by multiconfigurational \emph{ab-initio} calculations\footnote{S. Shaik, D. Danovich, W. Wu, P. Su, H. Rzepa, P. Hiberty, \emph{Nat. Chem.} {\bf 4}, 195 (2012)}. However, the interpretation of these calculations has caused debate, with some research preferring the notion of a double, triple, or quasi double-triple bond, while other studies note that there is not enough evidence to clearly define the bonding nature of C$_2$\footnote{R. Zhong, M.Zhang, H. Xu, Z. Su, \emph{Chem. Sci.} {\bf 7}, 1028 (2016)}. In this work, photoelectron spectra of the C$_2^-$ anion are measured using a high resolution photoelectron imaging (HR-PEI) spectrometer. The electron anisotropy of the detachment reveals the character of the parent anion orbital. Detachment to both the ground $\tilde{X} ^1\Sigma_g^+$ and first excited $\tilde{a} ^3\Pi_u$ electronic states is observed, identifying the character of two orbitals: the diffuse detachment orbital of the anion, and the HOMO of the neutral. The measurements show that electron detachment occurs from a pure s-like orbital ($3\sigma_g$) and a dominant p-like orbital (1$\pi_u$), that is inconsistent with the predictions of strongly mixed (50:50) sp orbitals required for the high bond order models, a result compatible only with the predictions of a C$=$C double bonding scheme. \makeatletter{\renewcommand*{\@makefnmark}{}\footnotetext{Research supported by the Australian Research Council Discovery Project Grant DP160102585.}\makeatother}
Issue Date:06/20/18
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:Conference Paper / Presentation
Other Identifier(s):WH01
Date Available in IDEALS:2018-08-17

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