THE PREDICTED INFRARED SPECTRUM OF THE HYPERMETALLIC MOLECULE CaOCa IN ITS LOWEST TWO ELECTRONIC STATES $\tilde{X}\;^{1}\Sigma_{\rm g}^+$ AND $\tilde{a}\;^{3}\Sigma_{\rm u}^+$

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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 $^{1}\Sigma_{\rm g}^+$ ground electronic state and a very low lying linear $\tilde{a}\;^{3}\Sigma_{\rm u}^+$ first excited triplet electronic state. For CaOCa we determine that the singlet-triplet splitting $T_{\rm e}(\tilde a)$ = 386 cm$^{-1}$. 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 $^{40}$Ca$^{16}$O$^{40}$Ca in each of these electronic states in order to aid in its eventual spectroscopic characterization.

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Author Institution: Institute of Chemistry, Technology and Metallurgy; University of Belgrade, Studentski trg 14-16, 11 000 Belgrade, Serbia; Centre for Theoretical Chemistry and Physics (CTCP); The New Zealand Institute for Advanced Study(NZIAS), Massey University Auckland; Private Bag 102904, North Shore City, 0745 Auckland, New Zealand; FB C -- Physikalische und; Theoretische Chemie, Bergische Universitat; D-42097 Wuppertal, Germany

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