FCN− and FNC− radical anions

Abstract

The radical anions FCN⁻ and FNC⁻ are studied at high ab initio levels of theory. Both anionic isomers possess a weak so-called three-electron bond, and highly correlated methods are necessary to predict their geometric parameters. At their respective equilibrium structures both anions represent electronically stable species but the associated neutrals FCN and FNC exhibit negative vertical electron affinities. Our computed electron affinities show that both anionic isomers are stable with respect to adiabatic electron loss. FCN⁻ represents the global minimum of the FCN-plus-electron system, and FNC⁻ can decay only ia rearrangement and simultaneous autodetachment, but is predicted to exhibit a very long lifetime. The temporary anion states associated with vertical electron attachment to the neutrals are investigated within the framework of the complex absorbing potential method. Short-lived ²Π resonance states are identified and predicted to be observable in an electron transmission experiment. In spite of their close relation, the two isomeric anions FCN⁻ and FNC⁻ show surprisingly different properties. FNC⁻ can be characterised as a typical pseudo-dihalogen anion, whereas FCN⁻ is more similar to the isovalent CO₂⁻.