Knowledge Bank

This study of CaOCa is the third in a series by us on Group 2 alkaline-earth M$2$O hypermetallic oxides. As with our previous calculations in the series, on BeOBe and MgOMg, the {\it ab initio} calculations we report here show that CaOCa has a linear $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma g+$ ground electronic state and a very low lying linear $a~3\Sigma u+$ first excited triplet electronic state. For CaOCa we determine that the singlet-triplet splitting $Te(a~)$ = 386 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. We calculate the three-dimensional potential energy surface, and the electric dipole moment surfaces, of each of the two states using a multireference configuration interaction (MRCISD) approach in combination with internally contracted multireference perturbation theory (RS2C) based on full-valence complete active space self-consistent field (FV-CASSCF) wavefunctions with a cc-pwCVQZ-DK basis set for Ca and a cc-pCVQZ basis set for O. We simulate the infrared absorption spectra of $\mathrm{<mrow\; data-mjx-texclass="ORD">40</mrow>}$Ca$\mathrm{<mrow\; data-mjx-texclass="ORD">16</mrow>}$O$\mathrm{<mrow\; data-mjx-texclass="ORD">40</mrow>}$Ca in each of these electronic states in order to aid in its eventual spectroscopic characterization.