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Title:Ro-vibrationally Averaged Molecular Structure Of Benzene     I. Almost The Same Bond Lengths For The C-h And C-d Bonds.
Author(s):Baba, Masaaki
Contributor(s):Hirano, Tsuneo; Nagashima, Umpei
Subject(s):Structure determination
Abstract:Contrary to the common sense that the C--H bond-length is longer than that of the C--D bond due to the anharmonicity of the potential, Baba group found, from high-resolution laser spectroscopy, that ro-vibrationally averaged bond lengths of C--H and C--D are observed as being almost identical ($r_{\rm 0,eff}$(C--H) $\cong$ $r_{\rm 0,eff}$(C--D)) for planar aromatic hydrocarbons, such as benzene\footnote{S. Kunishige, M. Baba, et al., J. Chem. Phys. {\bf 143}, 244302 (2015).}, naphthalene\footnote{M. Baba, U. Nagashima, et al., J. Chem. Phys. {\bf 135}, 054305 (2011).}, and anthracene\footnote{M. Baba, U. Nagashima, et al., J. Chem. Phys. {\bf 130}, 134315 (2009).}. The vibrationally averaged bond lengths of benzene deduced from experimental rotational constants and \textit{ab initio} geometry$^b$ are $r_0$(C--H) $=$ $r_0$(C--D) = 1.0831 {\AA}.$^a$ In this study, the vibrationally averaged structures of benzene are derived from the DVR (Discrete Variable Representation) wavefunction based on the 3D potential energy surface at the level of valence-CCSD(T)/[aVQZ(H,C)] theory. The zero-point C--H(D) bond-length, $r_{\rm 0,eff}$(C--H(D)), determined from the experimental effective rotational constants, is, in definition, the $r_{0}$ bond-length projected onto the $a$-$b$ principal axis plane, $r_{\rm 0,proj}$(C--H(D)). The DVR wavefunction gives $r_{\rm 0,proj}$(C--H) $=$ 1.0815 {\AA} and $r_{\rm 0,proj}$(C--D) $=$ 1.0819 {\AA}, so that the difference is of a negligibly small value $-$0.0004 {\AA}. Thus, the seemingly strange experimental finding ($r_{\rm 0,eff}$(C--H) $\cong$ $r_{\rm 0,eff}$(C--D)), which is controversial to the common sense, is resolved. The details will be given in the next presentation (part II.)
Issue Date:2021-06-25
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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