Knowledge Bank

All electron ab-initio Hartree-Fock(HF) and configuration interaction (CI) calculations have been performed on $Si2,Ge2,SiC$ and GeC molecules to predict the potential energy curves for the lowest lying electronic states. $Si2$ and $Ge2$ molecules show a similarity in their multiplet structure resulting in a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma g\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}(\pi u\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\sigma g\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>})$ ground state and a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\pi u(\pi u\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\sigma g)$ as the first excited state with a smaller energy separation from the ground state. SiC and GeC molecules exhibit a similarity in their multiplet structure with a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\pi (\pi 3\sigma )$ ground state and a $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma -(\pi 2\sigma 2)$ as the first excited state with an energy separation of $\simeq 0.8eV$ from the ground state. The spectroscopic constants have been calculated for the ground state and some of the excited states of the above molecules and compared with the available experimental data. The low lying electronic states are useful in an accurate evaluation of the dissociation energy of these molecules using mass spectrometric measurements.