MILLIMETERWAVE SPECTROSCOPY OF THE INTERNAL ROTATION BANDS OF Ne-DCN
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Date
2011
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Publisher
Ohio State University
Abstract
In 2005,, \textbf{RH01}, (2005).} we reported the MMW specrtum of internal rotation bands ($j$=1-0 and 2-1) of Ne-HCN to analyzed the intermolecular potential energy surface (PES) between Ne and HCN, where $j$ denotes the quantum number for the HCN internal rotation. In the present study, we have extended our observation to the Ne-DCN deuterated complex in the MMW region (78-175 GHz), and assigned the several DCN internal rotation bands such as the $j$=1-0 fundamental band ($\Sigma_1$-$\Sigma_0$ and $\Pi_1$-$\Sigma_0$) and the $j$=2-1 hot band ($\Sigma_2$-$\Sigma_1$, $\Pi_2$-$\Sigma_1$, $\Pi_2$-$\Pi_1$, and $\Delta_2$-$\Pi_1$) for the $^{20}$Ne-DCN and $^{22}$Ne-DCN complexes. In total, 69 and 12 lines have been assigned to the $^{20}$Ne-DCN and $^{22}$Ne-DCN. The intermolecular stretch band between Ne and DCN, however, was not observed in this frequency region. Analysis shows that the $\Sigma_1$ and $\Pi_1$ sublevels for $j$=1 state are located at 134 and 105 GHz, respectively, above the $j$=0 ground state ($\Sigma_0$), while the $\Sigma_2$, $\Pi_2$, and $\Delta_2$ sublevels of $j$=2 state are located at 286, 276, and 257 GHz with different order from that for the normal species. The observed MMW frequencies for Ne-DCN were analyzed with two dimensional ($\theta - R$) PES freezing the freedom in DCN moiety. The PES given by CCSD(T) level $ab~initio$ calculation \textbf{114}, 851 (2001).} was modified by adding sixteen extra parameters and fitted to the observed frequencies of internal rotation bands of both $^{20}$Ne and $^{22}$Ne species. The ($\theta - R$) PES thus fitted has a global minimum in the linear configuration (Ne$\cdots$D--C--N) with a well depth of 64.1 cm$^{-1} $, and a saddle point located in the anti-linear configuration (D--C--N$\cdots$Ne) by 18.4 cm$^{-1}$ higher than the global minimum. The $j$=0 ground vibrational state is located by 4.8 cm$^{-1}$ higher than the saddle point. The PES is anisotropic because the center-of-mass distance between Ne and DCN changes much along the minimum energy path, 4.230, 3.477, and 4.020 \AA\ in the linear, T-shaped, and anti-linear forms, together with their energies. The PES estimated for Ne-DCN is very similar to that of Ne-HCN, but the global minimum is by 1.1 cm$^{-1}$ deeper than that of Ne-HCN, due to the frozen model of the HCN/DCN moiety and also our observation is quite limited to the bottom of PES, e.g. highest observed state ($\Sigma_2$) is still 30 cm$^{-1} $ below the dissociation limit.
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Author Institution: Department of Chemistry, Faculty of Science, Kyushu University; Hakozaki, Higashiku, Fukuoka, 812-8581 JAPAN