Calculation of isotropic hyperfine coupling constants by the symmetry adapted cluster expansion configuration interaction theory

The isotropic hyperfine coupling constants (HFCCs) are calculated for H2O+⋅, CH2O+⋅, CH3O⋅, CH3NH⋅, CH3CH2⋅, and CH3OCH+⋅3, using the method of SAC (symmetry adapted cluster expansion)-CI. After examining various basis sets, we found that the double-zeta quality basis sets of Dunning are the best among the sets examined. The calculated values agree fairly well with the experimental values. We point out that the conventional configuration selection based on the energy criterion has an inherent limit for the calculation of HFCCs. The influence of molecular vibrations on the HFCCs has been semiquantitatively examined for CH2O+⋅, CH3O⋅, CH3NH⋅, and CH3CH⋅2.