Knowledge Bank

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 $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}$Ne-DCN and $\mathrm{<mrow\; data-mjx-texclass="ORD">22</mrow>}$Ne-DCN complexes. In total, 69 and 12 lines have been assigned to the $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}$Ne-DCN and $\mathrm{<mrow\; data-mjx-texclass="ORD">22</mrow>}$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 $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}$Ne and $\mathrm{<mrow\; data-mjx-texclass="ORD">22</mrow>}$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} $,andasaddlepointlocatedintheanti-linearconfiguration(D--C--N$\cdots$Ne)by18.4cm$^{-1}$ higher than the global minimum. The $j$=0 ground vibrational state is located by 4.8 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ 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$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ 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.