CaF2 As a Quasilinear Molecule: the Vibrational−Rotational Energy Levels Predicted by Ab Initio Quantum Chemistry Approach

The equilibrium structure and potential-energy surface of calcium difluoride, CaF 2, have been determined from large-scale ab initio calculations using the coupled-cluster method, CCSD(T), in conjunction with basis sets of quadruple- and quintuple-ζ quality. The CaF 2 molecule was found to be quasilinear, with an equilibrium FCaF angle of 154.3° and barrier to linearity of 54 cm -1 . The vibrational−rotational energy levels of the 40 CaF 2 and 44 CaF 2 isotopomers were predicted using the variational method. In particular, the FCaF bending fundamental (the ν 2 mode) was determined to be very low at only 9 cm -1 . The calculated spectroscopic constants could be used to guide future high-resolution spectroscopic experiments on calcium difluoride.