THE RENNER-TELLER EFFECT FOR THE $^{2}\Pi$ ELECTRONIC EXCITED STATE OF MgCN; AN AB INITIO MOLECULAR ORBITAL PREDICTION

$^{a}$K. Ishii. T. Hirano. U. Nagashima, B. Weis, and K. Yamashita, Astrophys. J. 410. L43, (1993) $^{b}$K. Kawaguchi, E. Kagi. T. Hirano, S. Takano, and S. Saito, Astrophys. J. 406. L39. (1993) $^{c}$L. M. Ziurys. A. J. Apponi. M. Guelin, and J. Cemicharo Astrophys. J. 445, L47, (1995)Author Institution: Department of Chemistry, Faculty of Science, Ochonomizu University; National Institute for Advanced Interdisciplinary Research, Ibaraki 305-8562, Japan., Faculty of Science, Ochonomizu UniversityMgNC is the first Mg-bearing molecule in space identified by us through the cooperative studies between ab initio molecular orbital $calculations ^{a}$ and the laboratory microwave $study ^{b}$. MgCN is its isomer, and has also been identified in space by $ziurys et al.^{c}$ We have generated the potential energy surface of $^{2}\Pi$ electronic excited state of MgCN at the MRSDCI/aug-cc-pVQZ level of calculations, and predicted spectroscopic constants. The potential energy surface shows that MgCN has a linear structure in the $^{2}\Pi$ electronic state, which splits into two states, $^{2}A^{\prime}$ and $^{2}A^{\prime\prime}$ via Mg-C-N bending motions (Renner-Teller splitting). The Renner parameter $\epsilon$ is calculated as 0.24 for $^{2}\Pi$ in MgCN, which is smaller than the corresponding value for $^{2}\Pi$ in MgNC ($\epsilon=0.32)$