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 Title: AB INITIO CALCULATIONS ON ROTATIONAL CONSTANT AND AVERAGED C-H(D) BOND LENGTHS OF BENZENE Author(s): Baba, Masaaki Contributor(s): Nagashima, Umpei ; Hirano, Tsuneo Subject(s): Structure determination Abstract: Rotational constants in the ground states of benzene and its deuterated isotopologues were accurately determined by high-resolution spectroscopy [1]. It was demonstrated that the averaged bond length $r_{\mbox {\scriptsize{0,eff}}}$(C-H) is approximately identical to the $r_{\mbox {\scriptsize{0,eff}}}$(C-D). Bearing in mind that the experimentally observed rotational constants correspond to the averaged ro-vibrating structure projected onto each principal axis [2], we discussed this finding in terms of wavefunction for the local modes derived from the CCSD(T)/[aVQZ (C, H)] ab initio potential energy surface. Due to the anharmonicity in the C-H stretching motion, $r_{\mbox {\scriptsize{str,0}}}$(C-H) is calculated to be longer than $r_{\mbox {\scriptsize{str,0}}}$(C-D) by 0.0024 {\AA}. Since the vibrationally averaged projection-angle of the C-H(D) bond with respect to the principal axis is larger for the C-H bond (having lighter H atom) than the C-D bond, the projected bond-lengths $r_{\mbox {\scriptsize{proj,0}}}$(C-H) in the out-of-plane and in-plane bending motions become shorter than $r_{\mbox {\scriptsize{proj,0}}}$(C-D) by 0.0017 {\AA} and 0.0011 {\AA}, respectively. Thus, in the sum of $r_{\mbox {\scriptsize{str,0}}}$ and $r_{\mbox {\scriptsize{proj,0}}}$, the difference in $r_{\mbox {\scriptsize{0,eff}}}$(C-H) and $r_{\mbox {\scriptsize{0,eff}}}$(C-D) becomes negligibly small value of 0.0004 {\AA}, which explains why we observed $r_{\mbox {\scriptsize{0,eff}}}$(C-H) $\approx$ $r_{\mbox {\scriptsize{0,eff}}}$(C-D).\\[3mm] \begin{flushleft} [1] S. Kunishige, M. Baba, et al., {\it J. Chem. Phys.}, {\bf 143}, 244302 (2015). \\[3mm] [2] T. Hirano, U. Nagashima, and M. Baba, {\it J. Mol. Spectrosc.}, in press. \end{flushleft} Issue Date: 23-Jun-20 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/107356 Date Available in IDEALS: 2020-06-26
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