15min:

NAOKO OYAMADA, KENSUKE HARADA AND KEIICHI TANAKA, Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashiku, Fukuoka, 812-8581 JAPAN.

In 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 ( ₁- ₀ and ₁- ₀) and the j=2-1 hot band ( ₂- ₁, ₂- ₁, ₂- ₁, and ₂- ₁) for the ²⁰Ne-DCN and ²²Ne-DCN complexes. In total, 69 and 12 lines have been assigned to the ²⁰Ne-DCN and ²²Ne-DCN. The intermolecular stretch band between Ne and DCN, however, was not observed in this frequency region. Analysis shows that the ₁ and ₁ sublevels for j=1 state are located at 134 and 105 GHz, respectively, above the j=0 ground state ( ₀), while the ₂, ₂, and 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 ( - R) PES freezing the freedom in DCN moiety. The PES given by CCSD(T) level ab~initio calculation was modified by adding sixteen extra parameters and fitted to the observed frequencies of internal rotation bands of both ²⁰Ne and ²²Ne species. The ( - R) PES thus fitted has a global minimum in the linear configuration (Ne 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 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 Å 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 ( ₂) is still 30 cm^-1 below the dissociation limit.