Vibrational modulation effects on the hyperfine coupling constants of fluoromethyl radicals

A general quantum-mechanical protocol for the study of nonrigid free radicals has been applied to the series CH3, CH2F, CHF2, and CF3. Electronic structures have been computed by highly correlated ab initio methods and vibrational modulation effects have been studied by a nonrigid invertor Hamiltonian. The effect of small amplitude vibrations perpendicular to the inversion motion has been taken into account by an adiabatic model. The results are in close agreement with experiment, and can be interpreted quite straightforwardly in terms of the interplay between the potential energy and the property hypersurfaces. This allows a more dynamically based analysis of hyperfine coupling constants extensible to large, nonrigid radicals.