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MgNC is the first Mg-bearing molecule in space identified by us through the cooperative studies between ab initio molecular orbital $calculationsa$ and the laboratory microwave $studyb$. MgCN is its isomer, and has also been identified in space by $ziurysetal.c$ We have generated the potential energy surface of $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ electronic state, which splits into two states, $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A\prime$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A\prime \prime$ via Mg-C-N bending motions (Renner-Teller splitting). The Renner parameter $ϵ$ is calculated as 0.24 for $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ in MgCN, which is smaller than the corresponding value for $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ in MgNC ($ϵ=0.32)$.