The heaviest group 2 difluoride, RaF2: Geometry and ionization energy

The heaviest group 2 difluoride, radium difluoride (RaF2), is studied for t he first time. A basis set is employed for radium that combines an effectiv e core potential with a large, flexible valence space. This basis set is te sted by calculating the first and second ionization energies of Ra, where v alues in excellent agreement with experiment are obtained. MP2 ab initio ca lculations are employed to obtain the optimized equilibrium geometry and th e harmonic vibrational frequencies for the ground-state neutral and some of the low-lying cationic states. In addition, the optimized geometry of the ground-state neutral is obtained at the CCSD(T) level. The trend in geometr y of the group 2 difluorides is confirmed, with a angle FRaF bond angle of 118 degrees being calculated, together with a bond length of 2.30 Angstrom. It is concluded that involvement of the Ra 6p orbitals in the valence mole cular orbitals of RaF2 adequately explains its bent geometry. RCCSD(T) calc ulations are then employed to calculate ionization energies. The first adia batic ionization energy, corresponding to the ionization (X) over tilde (2) Sigma (+)(u) <-- (X) over tilde (1)A(1) is calculated to be 10.67 +/- 0.05 eV. The ordering of the ionic states is discussed in the light of the prese nt results. The polarizability of Ra was calculated to be 36.3 Angstrom (3) , with that of Ra2+ was calculated to be 1.97 Angstrom (3); the latter was employed in a simple ionic model, but this failed to calculate the ionizati on energy accurately.