Hartree–Fock electron affinity of the CN radical

Self-consistent-field calculations on CN(X 2Σ+) and CN−(X 1Σ+) have been performed at several internuclear separations. The estimated Hartree–Fock limit value for the adiabatic electron affinity of CN is 3.29±0.05 eV as compared with the observed value of 3.82±0.02 eV. A qualitative explanation has been proposed for the large electron affinity of CN.