Relation between electronic structure and the chemiluminescence arising from collisions between alkaline earth atoms and halogen molecules

The chemiluminescence ascribed by Jonah and Zare to radiative association of Ba and Cl2 is examined in the light of the electronic structure of the ground and excited states of alkaline earth dihalides. A simple discussion is first given in terms of the possible curve crossings and avoided crossings. In addition ab initio self-consistent-field calculations are reported for CaF2 using an extended basis set. The 1 B 2 excited state, from which the molecule may radiate to the ground state, is predicted to have an equilibrium bond angle of 54° and bond distance of 4·06 bohr. The bertical excitation energy to the 1 B 2 state is 7·3 eV and the vertical energy difference (1 A 1-1 B 2) at the 1 B 2 equilibrium geometry is 1·3 eV. These results appear consistent with the model proposed by Jonah and Zare. In addition, a variety of properties (dipole moments, field gradients, etc). of CaF2 are reported.