Nonempirical LCAO MO SCF studies of the group IIa dihalides BeF2, MgF2, and CaF2

Abstract

Nonempirical LCAO MO SCF calculations are reported for the ground, C_2ν states of the Group IIa dihalides, BeF₂, MgF₂, and CaF₂. These calculations demonstrate the importance of 3d orbitals in the bonding trends of the dihalides and, hence, in the determination of the equilibrium bond angles and the bending force constants. The calculations on BeF₂ indicate that d orbitals play an important role in the bonding but do not preferentially alter the general features of the total energy curve at any bond angle. In the case of MgF₂, d orbitals are found to preferentially lower the energy of the nonlinear configurations. However, for both species, the ground‐state equilibrium bond angle is predicted to be 180°. Configuration interaction studies also support the fact that, in the gas phase, the linear configuration is most stable. On the basis of s(1s, 2s, 3s, 4s, 2p, and 3p orbitals on Ca) basis set calculations, it is predicted that CaF₂ is linear. However, when 3d orbitals are added to the s basis set, the predicted equilibrium bond angle is 145°. This is in good agreement with the value of 141° deduced from matrix‐isolation spectroscopy. The bonding in these molecules is discussed with reference to the nonempirical molecular correlation diagram.