Theoretical study of vibronic coupling in the FCO2 radical

► Vibronic interactions between the X and B electronic states has been theoretically investigated. ► KDC model has been employed. ► Coupling constants have been calculated within the adiabatic quadratic approach. ► The inclusion of the vibronic couplings makes crucial changes in the potential surfaces. ► The calculated asymmetric ν5 and ν6 fundamental energies agree with the experiment.