Articles you may be interested inComment on ''Infrared spectrum and theoretical study of the dinitrogen pentoxide molecule (N2O5) in solid argon'' [A comparison of two approaches to perturbation triple excitation corrections to the coupledcluster singles and doubles method for highspin openshell systemsThe multireference MCSCF and MCSCFϩMP2 methods were applied to the study of the optimum geometry of the F 3 Ϫ anion, its vibrational frequencies and its dissociation energy into F 2 ϩF Ϫ . The system has a strong multireference character. The optimum geometry of the F 3 Ϫ anion doing a MCSCF͑3,4͒ or a MCSCF͑9,16͒ computation presents a symmetry breaking from D ϱh →C ϱv . Using other active spaces, like the one constructed following the orbital doubling technique, the symmetry breaking problem is solved. Finally, the accurate computation of the dissociation energy requires the inclusion of the dynamical correlation: the MCSCF dissociation energy is about 1 3 of the final MCSCFϩMP2 result. The best multireference results obtained here agree very well with the best monoreference results of Heard, Marsden, and Scuseria ͓G. L. Heard, C. J. Marsden, and G. Scuseria, J. Phys. Chem. 96, 4359 ͑1992͔͒ obtained with a QCISD͑T͒ and similar methods.