The heaviest group 2 Difluoride, RaF(2): geometry and ionization energy

The heaviest group 2 difluoride, radium difluoride (RaF(2)), is studied for the first time. A basis set is employed for radium that combines an effective core potential with a large, flexible valence space. This basis set is tested by calculating the first and second ionization energies of Ra, where values in excellent agreement with experiment are obtained. MP2 ab initio calculations are employed to obtain the optimized equilibrium geometry and the 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 geometry of the group 2 difluorides is confirmed, with an angle FRaF bond angle of 118 degrees being calculated, together with a bond length of 2.30 A. It is concluded that involvement of the Ra 6p orbitals in the valence molecular orbitals of RaF(2) adequately explains its bent geometry. RCCSD(T) calculations are then employed to calculate ionization energies. The first adiabatic ionization energy, corresponding to the ionization (tilde)X(2)Sigma(u)(+) <-- (tilde)X(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 present results. The polarizability of Ra was calculated to be 36.3 A(3), with that of Ra(2+) was calculated to be 1.97 A(3); the latter was employed in a simple ionic model, but this failed to calculate the ionization energy accurately.