AB-INITIO STUDIES OF X(3)(-) AND X(3) (X=F, CL)

The electronic structures, optimized geometries and harmonic vibrational frequencies of F3- Cl3-, F3 and Cl3 have been studied by ab initio calculations, using various basis sets and different correlation methods, including MP2, CISD and CASSCF. For the anions, reasonably consistent results were obtained for the closed-shell singlet ground states. However, for the open-shell doublet states of the neutral trihalogens and the triplet states of the anions the optimized geometries and hence the computed harmonic vibrational frequencies were found to be rather basis set and method dependent. Calculations based on a single configuration are inadequate for the neutral trihalogens, and the electronic structures of the various open-shell states of both the neutral trihalogens and their anions are rather complex. The different effects due to basis set size and dynamic and non-dynamic electron correlation on the various electronic structures, optimized geometries and computed harmonic vibrational frequencies obtained are discussed. Comparison with experimental data was made where available.