The predicted infrared spectrum of the hypermetallic molecule CaOCa in its lowest two electronic states X∼1Σg+ and a˜3Σu+

This study of CaOCa is our third paper in a series on Group 2 alkaline-earth M2O hypermetallic oxides. As with our previous calculations for BeOBe and MgOMg, the ab initio   calculations we report here show that CaOCa has a linear 1Σg+ ground electronic state and a very low lying linear a˜3Σu+ first excited triplet electronic state. For CaOCa we determine that the singlet–triplet splitting Te(a˜)=386cm-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 40Ca16O40Ca in each of these electronic states in order to aid in its eventual spectroscopic characterization.