The predicted infrared spectrum of the hypermetallic molecule CaOCa in its lowest two electronic states (X)over-tilde1Σg+; and (a)over-tilde3Σu+

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 1 Sigma(+)(g) ground electronic state and a very low lying linear (a) over tilde (3)Sigma(+)(u) first excited triplet electronic state. For CaOCa we determine that the singlet-triplet splitting T-e((a) over tilde) = 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 Ca-40 (OCa)-O-16-Ca-40 in each of these electronic states in order to aid in its eventual spectroscopic characterization. (C) 2012 Published by Elsevier B.V.