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Title:Vibrationally Averaged Structure And Frequencies Of (xehxe)+: Computational Molecular Spectroscopy Study
Author(s):Hirano, Tsuneo
Contributor(s):Baba, Masaaki; Nagashima, Umpei
Subject(s):Mini-symposium: Large Amplitude Motions
Abstract:We have proposed that the ro-vibrationally averaged structure of a linear molecule is observed as being ``bent.''\footnote{T. Hirano, U. Nagashima, P. Jensen, J. Mol. Spectrosc. \textbf{343}, 54 (2018); T. Hirano, U. Nagashima, M. Baba, J. Mol. Spectrosc. \textbf{369}, 111252 (2020); and references therein.} To provide more evidence for this assertion, we here chose a linear molecule (XeHXe)$^{+}$. We expected: The Xe atoms at both ends are so heavy that they stand still during vibration, so that in the bending mode, the central H$^{+}$ atom inevitably moves perpendicularly against the $a$ principal axis to give a ``bent'' ro-vibrationally averaged structure. The potential energy surface was calculated at the valence-CCSD(T){\_}DK3/[ANO-R3(Xe),cc-pV5Z-DK(H)] level, and ro-vibrational properties were calculated from the DVR3D wavefunctions in Discrete Variable Representation. The central H$^{+}$, which has +0.6 $e$ charge, polarizes the Xe atoms by its reaction field, giving 136 kcal/mol of the heat of formation: (XeHXe)$^{+}$ is a stable cation. The equilibrium structure for Xe1--H--Xe2 has $r_{\rm e}$(Xe1-H) = $r_{\rm e}$(H--Xe2) $=$ 1.8694 {\AA} and $\angle $(Xe1--H--Xe2) = 180$^{\circ}$, so that (XeHXe)$^{+}$ is a linear molecule. The ro-vibrationally averaged structure has $\langle r$(Xe1--H)$\rangle_{0}$ $=$ 1.8913 {\AA}, $\langle r$(H--Xe2)$\rangle_{0}$ $=$ 1.9017 {\AA}, and $\langle \angle$(Xe1--H--Xe2)$\rangle_0$ $=$ 166.6$^{\circ}$, indicating a large amplitude bending motion. The harmonic vibrational frequencies $\omega_1$ (antisymmetric stretch), $\omega_2$ (bending), and $\omega_3$ (symmetric stretch) are 824, 562, and 149 cm$^{-1}$, respectively. The corresponding term values $\nu_1$, $\nu_2$, and $\nu_3$ are 847, 545, and 143 cm$^{-1}$, respectively, to be compared with the values in \textit{para}-H$_{2}$ matrix\footnote{M. Tsuge, J. Kalinowski, R.B. Gerber, Y-P. Lee, J. Phys. Chem. A \textbf{119}, 2651 (2015)} $\nu_1$ $=$ 847.0 cm$^{-1}$ and $\nu_3$ $=$ 125.1 cm$^{-1}$. The relation $\nu_1$ $>$ $\omega_1$ is a typical feature for [(ultra)heavy--light--(ultra)heavy] system. In the antisymmetric stretch mode, the central H$^{+}$ moves back and forth between almost stand-still two Xe atoms just like a ball in catch-ball play, and hence the $\nu_{1}$ value is not affected by matrix medium. On the other hand, the symmetric stretching mode should severely be affected by the mass of the matrix medium, as is reported,$^{b}$ since Xe atoms in this mode have to push out the cavity wall of the matrix.
Issue Date:2021-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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