The polarization dependence on ε HOMO for the cations (Figure ) is split into two curves: an exponential one represented by H 3 O + , alkali metal cations, RMPyr + , and R 4 N + , and a linear one represented by CTA + , CP + , RMI + (except PhMI + , which is out of the trend), and RPy + . The dependence of P on ε LUMO , as the one for the dipole moment, decreases exponentially (Figure ), with TFSI -falling out of the trend. The maximum polarization values are obtained for the voluminous and heavy DS -and p-TsO -cations, the lowest ones for the light F -, OH -and BF 4 -ions.