The multiconfigurational-reference internally contracted configuration interaction/complete basis set study of the excited states of the trifluoride anion F3(-).

The multiconfigurational-reference internally contracted configuration interaction (MRCI)/aug-cc-pVQZ-based computational protocol was employed to search for the minima of the potential energy surface of the low-lying singlet and triplet electronic states of the trifluoride anion F(3) (-) in the D(infinity(h)), C(infinity(v)), C(2v), and C(s) symmetry groups. The (3)B(2) bound state was located (r(e)=1.8777 A and theta=103.39 degrees ), which was predicted to lie less than 1 eV above the X (1)Sigma(g) (+) ground state (r(e)=1.7382 A) by both the MRCI and equation-of-motion coupled-cluster singles, doubles and triples approaches [the MRCI adiabatic excitation energy extrapolated to the complete basis set (CBS) limit was 0.91 eV]. The latter value is proposed as a reliable estimate of the singlet-triplet energy gap in F(3) (-). The vertical transitions from the X (1)Sigma(g) (+) state were analyzed in terms of the reorganization of electrons leading to the excited states and the corresponding MRCI/CBS excitation energies.